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The aim of naval actions in World War I was to destroy the enemy’s ability to wage war by means of disrupting its commerce. A nation denied the ability to trade would lose its ability to feed and defend itself, and descend into economic chaos.International rules of conduct on the high seas during wartime were open to considerable interpretation. However, some principles were widely accepted:
- The merchant ships of enemy nations were legitimate targets, but provisions were to be made for the lives of the passengers and crews
- Neutral nations could conduct trade with belligerent nations in non-contraband items (contraband meaning goods used in waging war)
- Blockades (sealing off enemy ports by other warring parties) had to be active and effective in order to be recognized internationally; this rule was accepted as a means to prevent a belligerent from declaring a “paper blockade,” the practice of declaring a blockade without the means to actually stop ships from entering the specified ports.
President Wilson was firmly committed to keeping the United States out of the war. He issued a proclamation of neutrality on August 4 and made nine other such declarations over the next few months. However, the country's need to remain viable on the seas would quickly provoke problems with both of the major belligerents.Neutral Rights and BritainFrom the perspective of the United States, the first crisis on the seas was not German submarine warfare, but the British blockade policy. The British had acted with dispatch when the war began, declaring a blockade of German ports and laying mines in the North Sea; their control extended to all areas except the Baltic Sea. They also began the practice of stopping neutral ships (including those of the United States) on the high seas in order to examine cargoes. Some American ships were taken into British ports and detained for months; mail was seized and closely scrutinized by British intelligence. A further irritant was introduced when the British unilaterally broadened the meaning of contraband to include food and other normal trade items destined for the continent.These British rules were the subject of numerous diplomatic exchanges between the two nations. Relations were frequently strained, but did not develop to the extent that war was contemplated. American shipping interests that suffered losses at British hands generally believed that financial settlements would be made at the end of the war. British policies caused inconveniences for Americans, but not the loss of lives.German Warfare on the SeasThe German government resented the rather cozy relationship between the United States and Britain. They objected to the fact that the Americans made only feeble protests against the British blockade of Germany and actively traded arms in English ports.The United States' first wartime loss on the seas occurred in January 1915, a few days before Germany declared the existence of a war zone around the British Isles. From February 4 onward, all enemy shipping encountered within the area was subject to attack and no guarantees were to be made for the safety of the passengers and crews. President Wilson reacted with a warning to Germany, informing them that they would be held to "strict accountability" for the safety of American lives.The Germans maintained with good reason that traditional rules of the sea could not be observed by the commanders of their submarines (unterzeebooten or U-boats). The hulls of these boats were easily breached, making it very unwise to hail and warn an enemy vessel before attacking.Little notice was taken of the U-boat attack on an American tanker in early May, but an eruption of public fury followed the sinking of the Lusitania on May 7. Wilson resisted calls for military action and devoted his energies to diplomacy. Secretary of State William Jennings Bryan resigned during this crisis; he was not alone in his opinion that Wilson was leaning too far in Britain's direction. Many Americans in the West and South wondered how some citizens could contemplate involvement in a European conflict; in 1915, pro-war sentiment was largely confined to the Eastern maritime states.Wilson's and new Secretary of State Robert Lansing's protests drew the desired response from Germany—attacks on passenger ships were halted for the time being.However, in August, the British liner Arabic was sunk with the loss of two American lives. Formal protests brought German promises of reformed policies for passenger ships in the "Arabic Pledge." Nevertheless, an Italian liner was torpedoed by an Austrian U-boat in November.The next crisis occurred in March 1916, when the French steamer Sussex was torpedoed in the English channel; one American was killed. Wilson threatened a diplomatic rupture, eliciting the "Sussex Pledge" (May 1916) from the German government.Nine months of relative calm on the seas followed the Sussex crisis, but on January 31, 1917 Germany announced the resumption of unrestricted submarine warfare. The General Staff was convinced that they had U-boat strength great enough to defeat the British fleet and force a surrender before the United States would be able to enter the conflict.On February 3, 1917 President Wilson announced the severing of diplomatic ties with Germany.
Submarine Warfare. Modern navies employed submarines in combat, using their ability to proceed submerged, although not necessarily for an entire cruise. Their concealment meant that submarines were also ideal for allowing a weaker naval power to attack a stronger one. Smaller, less heavily armed, slower, and less expensive than many surface warships, submarines could nonetheless employ a sort of guerrilla warfare at sea, using surprise and attacking the weakest points of their opponents' navies and maritime trade to great effect.
The large‐scale use of submarines against surface warships began in World War I both sides employed them in that role. German successes overshadowed those of the Allies, primarily because there were few German surface ships, which robbed Allied craft of targets. Still, both sides succeeded in sinking opposing warships, and the threat of submarines caused commanders to exercise greater caution in using their fleet units.
But it was the attack on Allied merchant shipping by German submarines (Untersee boats or U𠄋oats) that drew the most attention during World War I. The U𠄋oats' ability to slip past the Allied naval blockades of German ports allowed them to gain access to British sealanes, attacking shipping headed for Great Britain. When Royal Navy defensive measures made it difficult for surfaced U𠄋oats to stop merchant ships at sea and board them, the German Navy resorted to “unrestricted submarine warfare,” that is, sinking merchant shipping without warning. Such a German sinking of the Lusitania, in 1915, led to a dramatic worsening of relations with the neutral United States, and the return of the more limited submarine attacks. Germany's political and military leadership gambled in 1917 on a resumption of unrestricted submarine warfare to win the war quickly on neutral as well as belligerent shipping. This prompted the United States to enter on the Allied side in April 1917. Though the Germans sank over 11 million tons of ships, the submarine offensive failed to strangle trade with Britain due to the introduction of protected convoys of merchant ships by the Allies, and the availability of merchant vessels from neutral countries to help replace losses. The threat of submarine attack did compel the U.S. Navy to defend its troopship convoys across the Atlantic, a task accomplished without loss.
The U𠄋oat campaign of World War II again raised the question of neutral American shipping and the possibility of German attacks. In response, President Franklin D. Roosevelt extended a “neutrality zone” eastward from the North American coast ultimately to Iceland, patrolled by U.S. Navy warships before the official American entry in the war. On several occasions, U𠄋oats clashed with American warships, in one case sinking the destroyer Reuben James in October 1941. After American entry into World War II, U𠄋oats initially decimated American East Coast shipping almost with impunity. With the introduction of adequate antisubmarine forces, convoying, and decryption of German naval signals, however, American losses fell dramatically, and the U.S. Navy and Allied forces took the war to the U𠄋oats in the central Atlantic with deadly effect.
Perhaps the most effective submarine campaign in history was the American Pacific Ocean submarine operation in World War II. This entailed many difficulties initially, including a dearth of bases, faulty torpedoes, and many cautious submarine commanders. Submarine crews spent eight weeks at a time on patrol under cramped conditions and with few amenities. Still, submarines played a vital reconnaissance role from the start of the conflict. Eventually aided by radar, the decryption of Imperial Japanese Navy radio signals (MAGIC), and improved torpedoes, the greatly expanded submarine force scored notable sinkings, destroying one Japanese battleship, eight aircraft carriers, and eleven cruisers. More significantly, the U.S. Navy's submarines crippled Japan's merchant marine, sinking 5.3 million tons, or over half of its ships, in the most successful campaign of the war. Groups of U.S. Navy submarines also emulated the German Navy's “wolf‐pack” tactics to great effect against Japanese convoys. In the war's last days, American submarines ranged over the entire Pacific, even entering the Japanese Inland Sea. But these accomplishments came at a price 22 percent of submarine personnel died during the conflict, the highest of any American service.
Following World War II, submarines gained new propulsion—nuclear𠄏ueled. One of the new roles was in antisubmarine warfare, using their own concealed operations, as well as improved sonar and radar, to find opposing submarines. Another was submarine‐launched ballistic missiles as a part of the nuclear deterrent of the superpowers. Submarine combat operations remained limited after 1945, however. Just one ship𠅊n Argentine cruiser—was sunk by a Royal Navy submarine during the Falkland War in 1982.
[See also Navy Combat Branches: Submarine Forces Submarines.]
Edward Beach , Run Silent, Run Deep , 1955.
Clay Blair , Silent Victory , 1975.
Mark P. Parillo , The Japanese Merchant Marine in World War II , 1993.
I. J. Galantin , Submarine Admiral , 1995.
Clay Blair , Hitler's U𠄋oat War , 1996.
Peter Padfield , War Beneath the Sea , 1996.
Submarine History - 20th Century
In the year 2000 the American submarine force celebrated the first century of service by highly skilled people in some of the most technologically advanced vessels ever built. The previous 100 years witnessed the evolution of a force that mastered submersible warfare, introduced nuclear propulsion to create the true submarine, and for decades patrolled the deep ocean front line the hottest part of an otherwise Cold War.
The Navy to acquired its first submarine in 1900. Overcoming competition from fellow American inventor, Simon Lake, Holland sold his newest model, Holland VI , to the Navy for $160,000 on 11 April. This 64-ton submarine was commissioned as USS Holland , or SS-1 , on 12 October of the same year.
For his sixth submarine, Holland introduced a new method of propulsion using a gasoline engine. Holland designed a small, lightweight gasoline engine that turned a propeller while the boat cruised on the surface. The engine ran a generator, a machine that produces electricity, to charge batteries necessary to run an electric motor during underwater operations. Although the gasoline engine worked well on paper, the engine had flaws. Gasoline is highly flammable and unstable. Using this fuel in a confined environment, such as the submarine, endangered the crew. Another danger were the batteries that ran the electric motor during underwater travel. They were heavy, bulky, terribly inefficient, and potentially explosive. Finding a safer means of propulsion was needed if the submarine was ever to submerge for long periods of time. Around the same time Holland was creating his submarines, German scientist Rudolf Diesel developed an excellent substitute for the gasoline engine. Diesel's engine used a fuel that was more stable than gasoline and could be stored safely. The engine also did not need an electric spark to ignite the fuel, adding another element of safety. These advantages, plus improved fuel economy, granted submarines with Diesel engines longer and safer cruises on the surface. While underwater, batteries were still necessary to provide power.
Due to the volatility of gasoline, American submersible designs soon followed the French practice, adopting the diesel engine in 1909 with the Electric Boat Company's F class (SS-20 through 23), built at Union Iron Works in San Francisco. After 1909, Diesel engines would be used in American submarines for nearly 50 years.
Combining the influence of diesel propulsion with the submersible designs of Holland and Lake, American submersibles took on a familiar configuration through American entry into the Great War. Submarines of the E, H, K, L, M, N, O, and R classes ranged in displacement from 287 to 510 tons, with the fastest boats displaying a top surface speed of barely 14 knots on diesel power.
During World War I the U.S. Navy separated these submersibles into two groups according to mission. "Boats" of the N and O classes, as well as some of the E type, patrolled American coasts and harbors following a defensive strategy.
Other submarines drew assignments that sent them to hostile European waters after 1917. Some K-, L-, O-, and E-class boats conducted offensive, open-sea operations from the Azores and Bantry Bay in Ireland. They supported the Allied effort to maintain open sea lanes along the European coast and in the approaches to the British Isles.
The Navy Department's plans for these vessels reflected the prevailing surface warfare thinking, which perceived the submersible as a type of destroyer or torpedo boat that should operate with the battle fleet. Thus the first foray into submarine design by the Bureau of Construction and Repair and the Bureau of Steam Engineering produced the faster 15-knot, 800-ton, S-class submarine in 1916 with the assistance of Electric Boat Company and Lake Torpedo Boat Company. At virtually the same time, Electric Boat received a commission to design the three boats of the 20-knot T, or AA class, with a normal displacement of 1107 tons. On paper these characteristics, adopted during the First World War, brought the Navy one step closer to the "fleet submarine," a submersible that could keep pace with the battle fleet.
The German U-boats of the 1914-1918 conflict gave American officers and designers reason for pause. Physically durable, powered by very reliable diesels, technically blessed with very long sea legs, they provided the paradigm for American interwar development. At the same time, the 1916-vintage American S-class proved a virtual clinic for basic design mistakes, burdened with difficult metallurgical problems and very unreliable diesels.
While Rear Admirals Harry Yarnell and Samuel Robinson, successive interwar chiefs of the Bureau of Engineering, worked to remedy the technical flaws with solutions from European and American engineering practice, the community of submarine officers struggled with a problem even more fundamental than propulsion. How should the Navy use submarines? What was their proper strategic role? During the interwar period influential officers like Captains Thomas Hart and Yates Stirling Jr., Admirals Henry Wiley and Frank Schofield, and the innovative Commander Thomas Withers debated these issues with the German paradigm in mind. Unfortunately, this model did not offer easy direction. While the German commercial warfare strategy and independent patrol tactics had great effect on the war effort of the Entente and its allies, incidents like the sinking of the passenger liner RMS Lusitania painted this style of warfare with a dark brush, suggesting immorality when submersibles operated without restriction.
Only a subtle formula could help American submariners address questions of identity and mission in such a political environment. Since the state of design and propulsion technology would not permit American industry to build a submarine durable and fast enough to keep pace with the battlefleet, operating with surface ships on a regular basis seemed unlikely. This forced submarine strategists like Withers to look more closely at independent patrols and a model that approximated the World War I German experience. In isolationist postwar America, however, this option brought with it the ethical burden of unrestricted U-boat warfare and civilian casualties, something a Navy diminished by the Washington Treaties did not care to assume. Thus, American submarine strategy could not include unrestricted submarine warfare, which might turn neutral commercial vessels and innocent civilians into victims.
American officers realized that war in all of its brutality, not peacetime politics or worthy ethical concerns, would determine the future challenges faced by the submarine force. In spite of official policy, the boats under construction in the 1930s reflected assertive, offensive strategic thinking as the country came to terms with the Depression under Franklin Roosevelt and the Bureaus of Construction and Repair and Engineering resolved the submarine engineering and propulsion dilemmas. The new Salmon - Sargo designs were intended for long-range independent patrols, with requisite food, fuel, and weapons capacity. In addition, the fleet exercises and war game scenarios during the late 1930s permitted these vessels to attack warships, convoy escort ships, and even certain convoys identified as critical to enemy logistical support. By 1940, the submarine force had answered its fundamental strategic questions and had the vessels to carry out the consequent roles and missions. Thus, when Admiral Thomas Hart proclaimed unrestricted submarine warfare against Japan on 8 December 1941, it came as no surprise. The submarine force knew what to do.
At the outbreak of hostilities with Japan on December 7, 1941, the United States had a number of small diesel-powered submersible ships (known, somewhat improperly, as "submarines) in the United States Navy. The lessons taught by successful German U-Boat campaigns in the Atlantic and the necessities of war in the Pacific dictated the need for large fast vessels that could run fast on the surface, bombard shore-based and surface targets with deck guns, conduct effective anti-aircraft defense, and remain in service during prolonged cruises with as many as 24 torpedoes, 40 mines, and fuel and food for 90 days.
Upon entering the war, the United States began turning out subs as fast as possible, and continued to do so on through WWII. The purpose of a submarine during WWI and WWII was simply to sink other ships. These "Fleet Boats" worked in concert with the surface fleet to track down and eliminate threats, often well into enemy controlled seas. Fleet boats, aesthetically, are little different from their surface counterparts - they had a flat deck, a pointed prow or nose, a conning tower, and surface armament in the form of several anti-aircraft machine guns and a larger deck gun for use against lightly-armored surface vessels. The batteries of these older subs did not store enough electricity to allow the ship to stay under for very long. Because of this, the ships were designed for maximum surface handling characteristics, where they spent the majority of their time.
These early submarines only submerged to escape detection. The U.S. Balao class, for instance, had a battery endurance of 48 hours at a meager two knots. Battery power was drained more quickly if the sub tried to travel faster. On the surface the fleet boats kept up with surface ships, maintaining a speed of about 21 knots. When submerged, most fleet boats could only dive to a maximum of around 400 feet. This is shallow compared to modern subs, which can dive to more than twice that depth.
The American submarines in WWII included three separate types or classes, Gato, Balao, and the later Tench, which were all virtually identical. Some 311 feet long with a beam of 27 feet, these fleet ships were made to knife through the water on the surface. Gato and Balao were heavily armed with ten torpedo tubes, six forward, four aft. They carried a large store of torpedoes, but were also armed with more conventional weapons as well. Balao, the most numerous class of American fleet subs, was armed with a forward facing five-inch deck gun, and four machine guns, which was a typical arrangement at the time. Each sub carried a limited store of torpedoes, no matter how long their patrol might be. Often commanders would opt to save a torpedo and sink a stricken enemy vessel with surface weapons, unless the target was heavily armored.
Employing the extremely reliable boats of the Gato , Balao , and Tench classes, the submarine force scored the most complete victory of any force in any theater of the war. In spite of a hesitant beginning due to the Pearl Harbor surprise and difficulties with defective torpedoes, the submarine force destroyed 1,314 enemy ships for 5.3 million tons which translated into fifty-five percent of all enemy ships lost. Out of 16,000 submariners, the force lost 375 officer and 3,131 enlisted men in fifty-two submarines, the lowest casualty rate of any combatant submarine service on any side in the 1939-1945 conflict.
While the Japanese advanced quickly after Pearl Harbor and the Navy struggled to recover from 7 December 1941, the submarine force brought the war to the enemy operating from Pearl Harbor, and Australian bases at Freemantle, and Brisbane. Submarines played a variety of roles in the war effort, demonstrating the versatility of stealth.
Among those allied warships regularly able to penetrate Japanese controlled areas, American submarines had extraordinary success against both Japanese merchantmen and warships. In the late summer of 1942, Lieutenant Commander Henry C. Bruton in command of USS Greenling on her third war patrol destroyed 32,050 tons of enemy merchant shipping and damaged a 22,000 ton converted carrier. Bruton ended the war ranked thirteenth among the submarine force's aces.
Refining their methods of attack made American submariners the worst enemy of any ship flying the Japanese flag. In early 1943, USS Wahoo put to sea on her third war patrol under the command of Lieutenant Commander Dudley W. Morton. Morton and his executive officer, Lieutenant Richard O'Kane, implemented and further refined a new method of attack suggested by Admiral James Fife, commander of the American submarines operating out of Brisbane. While O'Kane manned the periscope and made all of the observations, Morton was left free to evaluate the entire combat situation, making possible swift, informed, and effective approach and attack decisions.
The talent of Morton and O'Kane as well as their new command and control procedure enabled Wahoo to sink 31,890 tons of Japanese shipping on that patrol. Morton received the first of four Navy Crosses and his ship took home a Presidential Unit Citation. Later in the war, as commanding officer of USS Tang , Richard O'Kane received the Congressional Medal of Honor and became the Submarine Force's leading ace of the war, credited with destroying 31 ships for 227,800 tons.
In addition, Submarines played both humane and special operations roles in their campaign against Japan. In many of the hardest fought battles of the war submarine crews rescued unlucky carrier pilots who ended up in the sea, like future president George Bush. Fleet submarines also delivered troops tasked with special missions against Japanese Pacific strongholds. In August 1942, USS Nautilus [SS-169] and USS Argonaut [SS-166] delivered Marine Colonel Evans F. Carlson's "Raiders" to Makin Island. Upon completing their mission to reconnoiter the island and destroy its most important facilities, the two submarines picked up the Marines and returned to Pearl Harbor.
In the final months of the war, American submarines had difficulty finding targets because the Japanese had virtually no ships left to sink. Undaunted, submarine, submarine commanders pursued the enemy into his harbors and hiding places. Employing newly developed FM sonar sets, American submarines penetrated the minefields of closely guarded Japanese home waters to seek out warships and supply ships at anchor. There was no place to hide. The silent victory was complete.
In the conflict against Japan in World War II, the role and importance of the submarine forces of the United States cannot be overestimated. American submarines sank more than 600,000 tons of enemy warships and more than 5,000,000 tons of merchant shipping, thus destroying much of Japan's ocean commerce. This was accomplished by a force that never numbered more than two percent of naval personnel engaged in the war. The American submarine war against Japan created a blockade that denied her the oil, iron ore, food, and other raw materials she needed to continue to fight. By 1945 this submarine war made it impossible for any Japanese ship to sail the ocean. Without this commerce and the raw materials it supplied to her war effort, Japan found it impossible to continue the war outside of the homeland. No other WWII submarine remains that sank more ships than the USS Silversides.
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The concept of underwater combat has roots deep in antiquity. There are images of men using hollow sticks to breathe underwater for hunting at the temples at Thebes, but the first known military use occurred during the siege of Syracuse (415–413 BC), where divers cleared obstructions, according to the History of the Peloponnesian War. At the siege of Tyre (332 BC), Alexander the Great used divers, according to Aristotle. Later legends from Alexandria, Egypt from the 12th century AD, suggested that Alexander conducted reconnaissance, using a primitive submersible in the form of a diving bell, as depicted in a 16th-century Islamic painting. [ citation needed ]
According to a report attributed to Tahbir al-Tayseer in Opusculum Taisnieri published in 1562:
two Greeks submerged and surfaced in the river Tagus near the City of Toledo several times in the presence of The Holy Roman Emperor Charles V, without getting wet and with the flame they carried in their hands still alight. 
Although there were various plans for submersibles or submarines during the Middle Ages, the Englishman William Bourne designed one of the prototype submarines in 1578. This was to be a completely enclosed boat that could be submerged and rowed beneath the surface. Comprising a completely enclosed wooden vessel sheathed in waterproofed leather, it was to be submerged by using hand-operated wooden screw thread adjustable plungers pressing against flexible leather bags located at the sides to increase or decrease the volume of water to adjust the buoyancy of the craft. The sketch (left) suggests that the depth adjustment was utilizing a crankset projecting above the surface. There is no obvious accommodation for crew.   In 1596 the Scottish mathematician and theologian John Napier wrote in his Secret Inventions the following: "These inventions besides devises of sayling under water with divers, other devises and strategems for harming of the enemyes by the Grace of God and worke of expert Craftsmen I hope to perform." It is unclear whether or not Napier ever carried out his plans. Henry Briggs, who was professor of mathematics at Gresham College, London, and later at Oxford, was a friend of Napier, whom he visited in 1615 and 1616, and was also an acquaintance of Cornelius Van Drebbel, a Dutchman in the service of James I of England, who designed and built the first successful submarine in 1620. Hence, it is not impossible that it was because of the interest taken by Napier in the submarine that Briggs came in touch with Drebbel. 
Drebbel's submarine was propelled by oars. The precise nature of this submarine is unclear, it may be possible that it resembled a bell towed by a boat.  Two improved types were tested in the River Thames between 1620 and 1624.   Of one of these tests Constantijn Huygens reports in his autobiography of 1651 the following:
Worth all the rest put together is the little ship, in which he calmly dived under the water, while he kept the king and several thousand Londoners in the greatest suspense. The great majority of these already thought that the man who had very cleverly remained invisible to them – for three hours, as rumour has it – had perished, when he suddenly rose to the surface a considerable distance from where he had dived down, bringing with him the several companions of his dangerous adventure to witness to the fact that they had experienced no trouble or fear under the water, but had sat on the bottom, when they so desired, and had ascended when they wished to do so that they had sailed whithersoever they had a mind, rising as much nearer the surface or again diving as much deeper as it pleased them to do, without even being deprived of light yea, even that they had done in the belly of that whale all the things people are used to do in the air, and this without any trouble. From all this it is not hard to imagine what would be the usefulness of this bold invention in time of war, if in this manner (a thing which I have repeatedly heard Drebbel assert) enemy ships lying safely at anchor could be secretly attacked and sunk unexpectedly utilizing a battering ram — an instrument of which hideous use is made now- a-days in the capturing of the gates and bridges of towns. 
On 18 October 1690, his son Constantijn Huygens, Jr. commented in his diary on how Drebbel was able to measure the depth to which his boat had descended (which was necessary to prevent the boat from sinking) utilizing a quicksilver barometer:
Old Mistress Kuffler came to see me in the morning. She was still talking about a place at court or elsewhere I said I could not help her. She said that her father Cornelis Drebbel had a long tube of quicksilver in the boat in which he dived be under water. 
In order to solve the problem of the absence of oxygen, Drebbel was able to create oxygen out of saltpetre to refresh the air in his submarine. An indication of this can be found in Drebbel's own work: On the Nature of the Elements (1604), in the fifth chapter:
Very dry, subtle or warm air, which then very quickly penetrates the coarse, heavy clouds, expands them, makes them subtle and thin, and again changes them into the nature of air, whereby its volume is increased an hundredfold in a moment, which brings forth the terrific motion which, cracking and bursting, sets the air alight and moves it, until volume and density are equal, when there is rest. Thus is the body of the saltpetre broken up and decomposed by the power of the fire and so changed in the nature of the air, or as when a wet hand or cloth is waved about on a hot iron, or molten lead, which by expansion or enlargement due to heat cracks and bursts with a noise like thunder. 
The introduction of Drebbel's submarine concept seemed beyond conventional expectations of what science was thought to have been capable of at the time. Commenting on the scientific basis of Drebbel's claims, renowned German astronomer Johannes Kepler was said to have remarked in 1607: "If [Drebbel] can create a new spirit, by means of which he can move and keep in motion his instrument without weights or propelling power, he will be Apollo in my opinion." 
Although the first submersible vehicles were tools for exploring underwater, it did not take long for inventors to recognize their military potential. The strategic advantages of submarines were first set out by Bishop John Wilkins of Chester in Mathematical Magick in 1648:
- Tis private: a man may thus go to any coast in the world invisibly, without discovery or prevented in his journey.
- Tis safe, from the uncertainty of Tides, and the violence of Tempests, which do never move the sea above five or six paces deep. From Pirates and Robbers which do so infest other voyages from ice and great frost, which do so much endanger the passages towards the Poles.
- It may be of great advantages against a Navy of enemies, who by this may be undermined in the water and blown up.
- It may be of special use for the relief of any place besieged by water, to convey unto them invisible supplies and so likewise for the surprisal of any place that is accessible by water.
- It may be of unspeakable benefit for submarine experiments. 
Between 1690 and 1692, the French physicist Denis Papin designed and built two submarines. The first design (1690) was a strong and heavy metallic square box, equipped with an efficient pump that pumped air into the hull to raise the inner pressure. When the air pressure reached the required level, holes were opened to let in some water. This first machine was destroyed by accident. The second design (1692) had an oval shape and worked on similar principles. A water pump controlled the buoyancy of the machine. According to some sources, a spy of German mathematician Gottfried Wilhelm Leibniz called Haes reported that Papin had met with some success with his second design on the River Lahn. 
By the mid 18th century, over a dozen patents for submarines/submersible boats had been granted in England. In 1747, Nathaniel Symons patented and built the first known working example of the use of a ballast tank for submersion. His design used leather bags that could fill with water to submerge the craft. A mechanism was used to twist the water out of the bags and cause the boat to resurface. In 1749, the Gentlemen's Magazine reported that a similar design had been proposed by Giovanni Borelli in 1680. By this point of development, further improvement in design stagnated for over a century, until new industrial technologies for propulsion and stability could be applied. 
The carpenter Yefim Nikonov built the first military submarine in 1720 by order of Tsar Peter the Great in Russia. Nikonov armed his submarine with "fire tubes", weapons akin to flame-throwers. The submarine was designed to approach an enemy vessel, put the ends of the "tubes" out of the water, and blow up the ship with a combustible mixture. In addition, Nikonov designed an airlock for aquanauts to come out of the submarine and to destroy the bilge of the ship. With the death of Peter I in January 1725, Nikonov lost his principal patron and the Admiralty withdrew support for the project. [ citation needed ]
The first American military submarine was Turtle in 1776, a hand-powered egg-shaped (or acorn-shaped) device designed by the American David Bushnell, to accommodate a single man. It was the first submarine capable of independent underwater operation and movement, and the first to use screws for propulsion.  However, according to British naval historian Richard Compton-Hall, the problems of achieving neutral buoyancy would have rendered the vertical propeller of the Turtle useless. The route that Turtle had to take to attack its intended target, HMS Eagle, was slightly across the tidal stream which would, in all probability, have resulted in Ezra Lee becoming exhausted.  There are also no British records of an attack by a submarine during the war. In the face of these and other problems, Compton-Hall suggests that the entire story around the Turtle was fabricated as disinformation and morale-boosting propaganda, and that if Ezra Lee did carry out an attack, it was in a covered rowing boat rather than in Turtle. Replicas of Turtle have been built to test the design. One replica (Acorn), constructed by Duke Riley and Jesse Bushnell (claiming to be a descendant of David Bushnell), used the tide to get within 200 feet of the RMS Queen Mary 2 in New York City (a police boat stopped Acorn for violating a security zone).    Displays of replicas of Turtle which acknowledge its place in history appear in the Connecticut River Museum, the U.S. Navy's Submarine Force Library and Museum, Britain's Royal Navy Submarine Museum and Monaco's Oceanographic Museum. [ citation needed ]
In 1800, the French Navy built a human-powered submarine designed by Robert Fulton, the Nautilus. It also had a sail for use on the surface and so exhibited the first known use of dual propulsion on a submarine. It proved capable of using mines to destroy two warships during demonstrations. The French eventually gave up on the experiment in 1804, as did the British, when Fulton later offered them the submarine design. 
In 1834 the Russian Army General Karl Andreevich Shilder [ru] demonstrated the first rocket-equipped submarine to Emperor Nicholas I. 
The Submarino Hipopótamo, the first submarine built in South America, underwent testing in Ecuador on September 18, 1837. Its designer, Jose Rodriguez Lavandera, successfully crossed the Guayas River in Guayaquil accompanied by Jose Quevedo. Rodriguez Lavandera had enrolled in the Ecuadorian Navy in 1823, becoming a Lieutenant by 1830. The Hipopotamo crossed the Guayas on two more occasions, but it was abandoned because of lack of funding and interest from the government. 
In 1851 a Bavarian artillery corporal, Wilhelm Bauer, took a submarine designed by him called the Brandtaucher (fire-diver) to sea in Kiel Harbour. Built by August Howaldt and powered by a treadwheel, Brandtaucher sank, but the crew of three managed to escape. 
During the American Civil War both sides made use of submarines. Examples were the Alligator, for the Union, and the Hunley, for the Confederacy. The Hunley was the first submarine to successfully attack and sink an opposing warship. (see below)
In 1863 the Sub Marine Explorer was built by the German American engineer Julius H. Kroehl, and featured a pressurized work chamber for the crew to exit and enter underwater. This pre-figured modern diving arrangements such as the lock-out dive chamber, though the problems of decompression sickness were not well understood at the time.  After its public maiden dive in 1866, the Sub Marine Explorer was used for pearl diving off the coast of Panama. It was capable of diving deeper than 31 meters (103 feet), deeper than any other submarine built before. 
The Chilean government commissioned the Flach in 1865, during the Chincha Islands War (1864–1866) when Chile and Peru fought against Spain. Built by the German engineer Karl Flach, the submarine sank during tests in Valparaiso Bay on May 3, 1866, with the entire eleven-man crew.
During the War of the Pacific in 1879, the Peruvian government commissioned and built a submarine, the Toro Submarino. It never saw military action and was scuttled after Peru's defeat to prevent its capture by the enemy. 
The first submarine that did not rely on human power for propulsion was the French Navy submarine Plongeur, launched in 1863, and equipped with a reciprocating engine using compressed air from 23 tanks at 180 psi.  In practice, the submarine was virtually unmanageable underwater, with very poor speed and maneouverability. 
The first air independent and combustion powered submarine was the Spanish Ictineo II, designed by the Spanish engineer from Narciso Monturiol.  Originally launched in 1864 as a human-powered vessel, propelled by 16 men, it was converted to peroxide propulsion and steam in 1867. The 14 meters (46 feet) craft was designed for a crew of two, could dive to 30 metres (98 feet), and demonstrated dives of two hours. On the surface, it ran on a steam engine, but underwater such an engine would quickly consume the submarine's oxygen. To solve this problem, Monturiol invented an air-independent propulsion system. As the air-independent power system drove the screw, the chemical process driving it also released oxygen into the hull for the crew and an auxiliary steam engine. Apart from being mechanically powered, Monturiol's pioneering double-hulled vessels also solved pressure, buoyancy, stability, diving and ascending problems that earlier designs had encountered.
The submarine became a potentially viable weapon with the development of the first practical self-propelled torpedoes. The Whitehead torpedo was the first such weapon, and was designed in 1866 by British engineer Robert Whitehead. His 'mine ship' was an 11-foot long, 14-inch diameter torpedo propelled by compressed air and carried an explosive warhead. The device had a speed of 7 knots (13 km/h) and could hit a target 700 yards (640 m) away.  Many naval services procured the Whitehead torpedo during the 1870s and it first proved itself in combat during the Russo-Turkish War when, on 16 January 1878, the Turkish ship Intibah was sunk by Russian torpedo boats carrying Whiteheads.
During the 1870s and 1880s, the basic contours of the modern submarine began to emerge, through the inventions of the English inventor and curate, George Garrett, and his industrialist financier Thorsten Nordenfelt, and the Irish inventor John Philip Holland.
In 1878, Garrett built a 14-foot (4.3 m) long hand-cranked submarine of about 4.5 tons, which he named the Resurgam. This was followed by the second (and more famous) Resurgam of 1879, built by Cochran & Co. at Birkenhead, England.  The construction was of iron plates fastened to iron frames, with the central section of the vessel clad with wood secured by iron straps. As built, it was 45 feet (14 m) long by 10 feet (3.0 m) in diameter, weighed 30 long tons (30 t), and had a crew of 3. Resurgam was powered by a closed cycle steam engine, which provided enough steam to turn the single propeller for up to 4 hours. It was designed to have positive buoyancy, and diving was controlled by a pair of hydroplanes amidships. At the time it cost £1,538. 
Although his design was not very practical – the steam boiler generated intense heat in the cramped confines of the vessel, and it lacked longitudinal stability – it caught the attention of the Swedish industrialist Thorsten Nordenfelt. Discussions between the two led to the first practical steam-powered submarines, armed with torpedoes and ready for military use.
The first such boat was the Nordenfelt I, a 56 tonne, 19.5 metres (64 feet) vessel similar to Garret's ill-fated Resurgam, with a range of 240 kilometres (150 miles 130 nautical miles), armed with a single torpedo, in 1885. Like Resurgam, Nordenfelt I operated on the surface by steam, then shut down its engine to dive. While submerged, the submarine released pressure generated when the engine was running on the surface to provide propulsion for some distance underwater. Greece, fearful of the return of the Ottomans, purchased it. Nordenfelt commissioned the Barrow Shipyard in England in 1886 to build Nordenfelt II (Abdül Hamid) and Nordenfelt III (Abdül Mecid) in 1887.  They were powered by a coal-fired 250 hp Lamm steam engine turning a single screw, and carried two 356mm torpedo tubes and two 35mm machine guns. They were loaded with a total of 8 tons of coal as fuel and could dive to a depth of 160 feet. It was 30.5m long and 6m wide, and weighed 100 tons. It carried a normal crew of 7. It had a maximum surface speed of 6 knots, and a maximum speed of 4 knots while submerged. Abdülhamid became the first submarine in history to fire a torpedo submerged. 
Nordenfelt's efforts culminated in 1887 with Nordenfelt IV, which had twin motors and twin torpedoes. It was sold to the Russians, but soon ran aground and was scrapped. Garrett and Nordenfelt made significant advances in constructing the first modern, militarily capable submarines and fired up military and popular interest around the world for this new technology. However, the solution to fundamental technical problems, such as propulsion, quick submergence, and the maintenance of balance underwater was still lacking, and would only be solved in the 1890s. 
A reliable means of propulsion for submerged vessels was only made possible in the 1880s with the advent of the necessary electric battery technology. The first electrically powered submarines were built by the Polish engineer Stefan Drzewiecki in Russia, James Franklin Waddington and the team of James Ash and Andrew Campbell in England, Dupuy de Lôme and Gustave Zédé in France and Isaac Peral in Spain. 
In 1884, Drzewiecki converted 2 mechanical submarines, installing in each a 1 hp engine with a new, at the time, source of energy – batteries. In tests, the submarines travelled under the water against the flow of the Neva River at a rate of 4 knots. They were the first submarines in the world with electric propulsion. Ash and Campbell constructed their craft, the Nautilus, in 1886. It was 60 feet (18 m) long with a 9.7 kW (13 hp) engine powered by 52 batteries. It was an advanced design for the time, but became stuck in the mud during trials and was discontinued. Waddington's Porpoise vessel showed more promise. Waddington had formerly worked in the shipyard in which Garrett had been active. Waddington's vessel was similar in size to the Resurgam and its propulsion system used 45 accumulator cells with a capacity of 660 ampere hours each. These were coupled in series to a motor driving a propeller at about 750 rpm, giving the ship a sustained speed of 13 km/h (8 mph) for at least 8 hours. The boat was armed with two externally mounted torpedoes as well as a mine torpedo that could be detonated electronically. Although the boat performed well in trials, Waddington was unable to attract further contracts and went bankrupt. 
In France, the early electric submarines Goubet I and Goubet II were built by the civil engineer, Claude Goubet. These boats were also unsuccessful, but they inspired the renowned naval architect Dupuy de Lôme to begin work on his submarine – an advanced electric-powered submarine almost 20 metres long. He didn't live to see his design constructed, but the craft was completed by Gustave Zédé in 1888 and named the Gymnote. It was one of the first truly successful electrically powered submarines, and was equipped with an early periscope and an electric gyrocompass for navigation. It completed over 2,000 successful dives using a 204-cell battery.  Although the Gymnote was scrapped for its limited range, its side hydroplanes became the standard for future submarine designs.
The Peral Submarine, constructed by Isaac Peral, was launched by the Spanish Navy in the same year, 1888. It had three Schwartzkopff torpedoes 14 in (360 mm) and one torpedo tube in the bow, new air systems, hull shape, propeller, and cruciform external controls anticipating much later designs. Peral was an all-electrical powered submarine with an underwater speed of 3 kn (5.6 km/h 3.5 mph).  After two years of trials the project was scrapped by naval officialdom who cited, among other reasons, concerns over the range permitted by its batteries.
Many more designs were built at this time by various inventors, but submarines were not put into service by navies until the turn of the 20th century.
The turn of the 20th century marked a pivotal time in the development of submarines, with a number of important technologies making their debut, as well as the widespread adoption and fielding of submarines by a number of nations. Diesel electric propulsion would become the dominant power system and instruments such as the periscope would become standardized. Batteries were used for running underwater and gasoline (petrol) or diesel engines were used on the surface and to recharge the batteries. Early boats used gasoline, but quickly gave way to kerosene, then diesel, because of reduced flammability. Effective tactics and weaponry were refined in the early part of the century, and the submarine would have a large impact on 20th century warfare.
The Irish inventor John Philip Holland built a model submarine in 1876 and a full scale one in 1878, followed by a number of unsuccessful ones. In 1896, he designed the Holland Type VI submarine. This vessel made use of internal combustion engine power on the surface and electric battery power for submerged operations. Launched on 17 May 1897 at Navy Lt. Lewis Nixon's Crescent Shipyard in Elizabeth, New Jersey, the Holland VI was purchased by the United States Navy on 11 April 1900, becoming the United States Navy's first commissioned submarine and renamed USS Holland. 
A prototype version of the A-class submarine (Fulton) was developed at Crescent Shipyard under the supervision of naval architect and shipbuilder from the United Kingdom, Arthur Leopold Busch, for the newly reorganized Electric Boat Company in 1900. The Fulton was never commissioned by the United States Navy and was sold to the Imperial Russian Navy in 1905. The submarines were built at two different shipyards on both coasts of the United States. In 1902, Holland received U.S. Patent 708,553 for his relentless pursuit to perfect the modern submarine craft. Many countries became interested in Holland's (weapons) product and purchased the rights to build them during this time.
The Royal Navy commissioned the Holland-class submarine from Vickers, Barrow-in-Furness, under licence from the Holland Torpedo Boat Company during the years 1901 to 1903. Construction of the boats took longer than anticipated, with the first only ready for a diving trial at sea on 6 April 1902. Although the design had been purchased entirely from the US company, the actual design used was an untested improved version of the original Holland design using a new 180 hp petrol engine. 
Meanwhile, the French steam and electric Narval was commissioned in June 1900 and introduced the classic double-hull design, with a pressure hull inside the outer shell. These 200-ton ships had a range of over 100 miles (160 km) underwater. The French submarine Aigrette in 1904 further improved the concept by using a diesel rather than a gasoline engine for surface power. Large numbers of these submarines were built, with seventy-six completed before 1914. 
By 1914, all the main powers had submarine fleets, though the development of a strategy for their use lay in the future.
At the start of World War I, the Royal Navy had the world's largest submarine service by a considerable margin, with 74 boats of the B, C and D classes, of which 15 were oceangoing, with the rest capable of coastal patrols. The D-class, built 1907–1910, were designed to be propelled by diesel motors on the surface to avoid the problems with petrol engines experienced with the A class. These boats were designed for foreign service with an endurance of 2,500 nmi at 10 knots on the surface and much-improved living conditions for a larger crew. They were fitted with twin screws for greater maneuverability and with innovative saddle tanks. They were also the first submarines to be equipped with deck guns forward of the conning tower. Armament also included three 18-inch torpedo tubes (two vertically in the bow and one in the stern). D-class was also the first class of submarine to be equipped with standard wireless transmitters. The aerial was attached to the mast of the conning tower that was lowered before diving. With their enlarged bridge structure, the boat profile was recognisably that of the modern submarine. The D-class submarines were considered to be so innovative that the prototype D1 was built in utmost secrecy in a securely guarded building shed. 
The British also experimented with other power sources. Oil-fired steam turbines powered the British "K" class submarines built during the First World War and in following years, but these were not very successful. The aim was to give them the necessary surface speed to keep up with the British battle fleet.
The Germans were slower to recognize the importance of this new weapon. A submersible was initially ordered by the Imperial Russian Navy from the Kiel shipyard in 1904, but cancelled after the Russo-Japanese War ended. One example was modified and improved, then commissioned into the Imperial German Navy in 1906 as its first U-boat, U-1.   It had a double hull, was powered by a Körting kerosene engine and was armed with a single torpedo tube. The fifty percent larger SM U-2 had two torpedo tubes. A diesel engine was not installed in a German navy boat until the U-19 class of 1912–13. At the start of World War I, Germany had 20 submarines of 13 classes in service with more under construction. 
Diesel submarines needed air to run their engines, and so carried very large batteries for submerged travel. These limited the speed and range of the submarines while submerged.
An early submarine snorkel was designed by James Richardson, an assistant manager at Scotts Shipbuilding and Engineering Company, Greenock, Scotland, as early as 1916. The snorkel allowed the submarine to avoid detection for long periods by travelling under the water using non-electric powered propulsion. Although the company received a British Patent for the design,  no further use was made of it—the British Admiralty did not accept it for use in Royal Navy submarines. 
The first German U-boat to be fitted with a snorkel was U-58, which experimented with the equipment in the Baltic Sea during the summer of 1943. The technology was based on pre-war Dutch experiments with a device named a snuiver (sniffer). As early as 1938, a simple pipe system was installed on the submarines O-19 and O-20 that enabled them to travel at periscope depth operating on its diesels with almost unlimited underwater range while charging the propulsion batteries. U-boats began to use it operationally in early 1944. By June 1944, about half of the boats stationed in the French bases were fitted with snorkels. 
Various new submarine designs were developed during the interwar years. Among the most notable were submarine aircraft carriers, equipped with a waterproof hangar and steam catapult to launch and recover one or more small seaplanes. The submarine and its plane could then act as a reconnaissance unit ahead of the fleet, an essential role at a time when radar was not available. The first example was the British HMS M2, followed by the French Surcouf, and numerous aircraft-carrying submarines in the Imperial Japanese Navy.
Early submarine designs put the diesel engine and the electric motor on the same shaft, which also drove a propeller with clutches between each of them. This allowed the engine to drive the electric motor as a generator to recharge the batteries and also propel the submarine as required. The clutch between the motor and the engine would be disengaged when the boat dived so that the motor could be used to turn the propeller. The motor could have more than one armature on the shaft – these would be electrically coupled in series for slow speed and parallel for high speed (known as "group down" and "group up" respectively).
In the 1930s, the principle was modified for some submarine designs, particularly those of the U.S. Navy and the British U-class. The engine was no longer attached to the motor/propeller drive shaft, but drove a separate generator, which would drive the motors on the surface and/or recharge the batteries. This diesel-electric propulsion allowed much more flexibility. For example, the submarine could travel slowly whilst the engines were running at full power to recharge the batteries as quickly as possible, reducing time on the surface, or use of its snorkel. Also, it was now possible to insulate the noisy diesel engines from the pressure hull, making the submarine quieter.
An early form of anaerobic propulsion had already been employed by the Ictineo II in 1864. The engine used a chemical mix containing a peroxide compound, which generated heat for steam propulsion while at the same time solved the problem of oxygen renovation in an hermetic container for breathing purposes. This system wasn't employed again until 1940 when the German Navy tested a system employing the same principles, the Walter turbine, on the experimental V-80 submarine and later on the naval U-791 submarine. 
At the end of the Second World War, the British and Russians experimented with hydrogen peroxide/kerosene (paraffin) engines, which could be used both above and below the surface. The results were not encouraging enough for this technique to be adopted at the time, although the Russians deployed a class of submarines with this engine type code named Quebec by NATO. They were considered a failure. Today, several navies, notably Sweden, use air-independent propulsion boats, which substitute liquid oxygen for hydrogen peroxide.
For further information on nuclear powered submarines, see Nuclear submarine.
The first launch of a cruise missile (SSM-N-8 Regulus) from a submarine occurred in July 1953 from the deck of USS Tunny (SSG-282), a World War II fleet boat modified to carry this missile with a nuclear warhead. Tunny and her sister boat USS Barbero (SSG-317) were the United States' first nuclear deterrent patrol submarines. They were joined in 1958 by two purpose-built Regulus submarines, USS Grayback (SSG-574), USS Growler (SSG-577), and, later, by the nuclear-powered USS Halibut (SSGN-587). So that no target would be left uncovered, four Regulus missiles had to be at sea at any given time. Thus, Barbero and Tunny, each of which carried two Regulus missiles, patrolled simultaneously. Growler and Grayback, with four missiles, or Halibut, with five, could patrol alone. These five submarines made 40 Regulus strategic deterrent patrols between October 1959 and July 1964. They were replaced by the introduction of a greatly superior system beginning in 1961: the Polaris missile launched from nuclear-powered ballistic missile submarines (SSBNs). The Soviet Navy developed submarine-launched ballistic missiles launched from conventional submarines a few years before the US, and paralleled subsequent US development in this area.
In the 1950s, nuclear power partially replaced diesel-electric propulsion. The sailing of the first nuclear-powered submarine, the USN "Nautilus" in 1955 was soon followed by similar British, French and Russian boats. Equipment was also developed to extract oxygen from sea water. These two innovations, together with inertial navigation systems, gave submarines the ability to remain submerged for weeks or months, and enabled previously impossible voyages such as the crossing of the North Pole beneath the Arctic ice cap by the USS Nautilus in 1958. Most of the naval submarines built since that time in the United States and the Soviet Union and its successor state the Russian Federation have been powered by nuclear reactors. The limiting factors in submerged endurance for these vessels are food supply and crew morale in the space-limited submarine.
The Soviet Navy attempted to use a very advanced lead cooled fast reactor on Project 705 "Lira" (NATO Alfa-class) beginning in the 1970s, but its maintenance was considered too expensive, and only six submarines of this class were completed.  By removing the requirement for atmospheric oxygen all nuclear-powered submarines can stay submerged indefinitely so long as food supplies remain (air is recycled and fresh water distilled from seawater). These vessels always have a small battery and diesel generator installation for emergency use when the reactors have to be shut down.
While the greater endurance and performance of nuclear reactors mean that nuclear submarines are better for long distance missions or the protection of a carrier battle-force, both countries that do and countries that do not use nuclear power continue to produce conventional diesel-electric submarines, because they can be made stealthier, except when required to run the diesel engine to recharge the ship's battery. Technological advances in sound dampening, noise isolation and cancellation have substantially eroded this advantage. Though far less capable regarding speed and weapons payload, conventional submarines are also cheaper to build. The introduction of air-independent propulsion boats led to increased sales numbers of such types of submarines.
In 1958 the USN carried out a series of trials with the USS Albacore. Various hull and control configurations were tested to reduce drag and so allow greater underwater speed and maneuverability. The results of these trials were incorporated into the Skipjack class and later submarines. From the same era is the first SSBN, the USS George Washington.
The German Type 212 submarine was the first series production submarine to use fuel cells for air-independent propulsion. It is powered by nine 34-kilowatt hydrogen fuel cells.
Most small modern commercial submarines that are not expected to operate independently use batteries that can be recharged by a mother-ship after every dive.
Towards the end of the 20th century, some submarines were fitted with pump-jet propulsors, instead of propellers. Although these are heavier, more expensive, and often less efficient than a propeller, they are significantly quieter, giving an important tactical advantage.
A possible propulsion system for submarines is the magnetohydrodynamic drive, or "caterpillar drive", which has no moving parts. It was popularized in the movie version of The Hunt for Red October, written by Tom Clancy, which portrayed it as a virtually silent system. (In the book, a form of propulsor was used rather than an MHD.) Although some experimental surface ships have been built with this propulsion system, speeds have not been as high as hoped. In addition, the noise created by bubbles, and the higher power settings a submarine's reactor would need, mean that it is unlikely to be considered for any military purpose.
The first submarines had only a porthole to provide a view to aid navigation. An early periscope was patented by Simon Lake in 1893. The modern periscope was developed by the industrialist Sir Howard Grubb in the early 20th century and was fitted onto most Royal Navy designs. 
Passive sonar was introduced in submarines during the First World War, but active sonar ASDIC did not come into service until the inter-war period. Today, the submarine may have a wide variety of sonar arrays, from bow-mounted to trailing ones. There are often upward-looking under-ice sonars as well as depth sounders.
Early experiments with the use of sound to 'echo locate' underwater in the same way as bats use sound for aerial navigation began in the late 19th century. The first patent for an underwater echo ranging device was filed by English meteorologist Lewis Fry Richardson a month after the sinking of the Titanic.  The First World War stimulated research in this area. The British made early use of underwater hydrophones, while the French physicist Paul Langevin worked on the development of active sound devices for detecting submarines in 1915 using quartz. In 1916, under the British Board of Invention and Research, Canadian physicist Robert William Boyle took on the active sound detection project with A B Wood, producing a prototype for testing in mid-1917. This work, for the Anti-Submarine Division of the British Naval Staff, was undertaken in utmost secrecy, and used quartz piezoelectric crystals to produce the world's first practical underwater active sound detection apparatus.
By 1918, both France and Britain had built prototype active systems. The British tested their ASDIC on HMS Antrim in 1920, and started production in 1922. The 6th Destroyer Flotilla had ASDIC-equipped vessels in 1923. An anti-submarine school, HMS Osprey, and a training flotilla of four vessels were established on the English Isle of Portland in 1924. The US Sonar QB set arrived in 1931.
Weapons and countermeasures Edit
Early submarines carried torpedoes mounted externally to the craft. Later designs incorporated the weapons into the internal structure of the submarine. Originally, both bow-mounted and stern-mounted tubes were used, but the latter eventually fell out of favour. Today, only bow-mounted installations are employed. The modern submarine is capable of firing many types of weapon from its launch tubes, including UAVs. Special mine laying submarines were also built. Up until the end of the Second World War, it was common to fit deck guns to submarines to allow them to sink ships without wasting their limited numbers of torpedoes.
To aid in the weapons targeting mechanical calculators were employed to improve the fire control of the on-board weaponry. The firing calculus was determined by the targets' course and speed through measurements of the angle and its range via the periscope. Today, these calculations are achieved by digital computers with display screens providing necessary information on the torpedo status and ship status.
German submarines in World War II had rubber coatings and could launch chemical devices to provide a decoy when the boat came under attack. These proved to be ineffective, as sonar operators learned to distinguish between the decoy and the submarine. Modern submarines can launch a variety of devices for the same purpose.
After the sinking of the A1 submarine in 1904, lifting eyes were fitted to British submarines, and in 1908 air-locks and escape helmets were provided. The Royal Navy experimented with various types of escape apparatus, but it was not until 1924 that the "Davis Submerged Escape Apparatus" was developed for crew members. The USN used the similar "Momsen Lung". The French used "Joubert's apparatus" and the Germans used "Draeger's apparatus".
Rescue submarines for evacuating a disabled submarine's crew were developed in the 1970s. A British unmanned vehicle was used for recovering an entangled Russian submarine crew in 2005. A new NATO Submarine Rescue System entered service in 2007.
Communication and navigation Edit
Wireless was used to provide communication to and from submarines in the First World War. The D-class submarine was the first submarine class to be fitted with wireless transmitters in 1907. With time, the type, range and bandwidth of the communications systems have increased. With the danger of interception, transmissions by a submarine are minimised. Various periscope-mounted aerials have been developed to allow communication without surfacing.
The standard navigation system for early submarines was by eye, with use of a compass. The gyrocompass was introduced in the early part of the 20th century and inertial navigation in the 1950s. The use of satellite navigation is of limited use to submarines, except at periscope depth or when surfaced.
The first military submarine was Turtle in 1776. During the American Revolutionary War, Turtle (operated by Sgt. Ezra Lee, Continental Army) tried and failed to sink a British warship, HMS Eagle (flagship of the blockaders) in New York harbor on September 7, 1776. There is no record of any attack in the ships' logs.
During the War of 1812, in 1814 Silas Halsey lost his life while using a submarine in an unsuccessful attack on a British warship stationed in New London harbour.
American Civil War Edit
During the American Civil War, the Union was the first to field a submarine. The French-designed Alligator was the first U.S. Navy sub and the first to feature compressed air (for air supply) and an air filtration system. It was the first submarine to carry a diver lock, which allowed a diver to plant electrically detonated mines on enemy ships. Initially hand-powered by oars, it was converted after 6 months to a screw propeller powered by a hand crank. With a crew of 20, it was larger than Confederate submarines. Alligator was 47 feet (14 m) long and about 4 feet (1.2 m) in diameter. It was lost in a storm off Cape Hatteras on 1 April 1863 while uncrewed and under tow to its first combat deployment at Charleston. 
The Intelligent Whale was built by Oliver Halstead and tested by the U.S. Navy after the American Civil War and caused the deaths of 39 men during trials. [ citation needed ]
The Confederate States of America fielded several human-powered submarines, including CSS H. L. Hunley (named for its designer and chief financier, Horace Lawson Hunley). The first Confederate submarine was the 30-foot-long (9.1 m) Pioneer, which sank a target schooner using a towed mine during tests on Lake Pontchartrain, but it was not used in combat. It was scuttled after New Orleans was captured and in 1868 was sold for scrap. The similar Bayou St. John submarine is preserved in the Louisiana State Museum. CSS Hunley was intended for attacking Union ships that were blockading Confederate seaports. The submarine had a long pole with an explosive charge in the bow, called a spar torpedo. The sub had to approach an enemy vessel, attach the explosive, move away, and then detonate it. It was extremely hazardous to operate, and had no air supply other than what was contained inside the main compartment. On two occasions, the sub sank on the first occasion half the crew died, and on the second, the entire eight-man crew (including Hunley himself) drowned. On 17 February 1864, Hunley sank USS Housatonic off the Charleston Harbor, the first time a submarine successfully sank another ship, though it sank in the same engagement shortly after signalling its success. Submarines did not have a major impact on the outcome of the war, but did portend their coming importance to naval warfare and increased interest in their use in naval warfare.
Russo-Japanese War Edit
On 14 June 1904, the Imperial Japanese Navy (IJN) placed an order for five Holland Type VII submersibles, which were built in Quincy, Massachusetts, at the Fore River Yard, and shipped to Yokohama, Japan in sections. The five machines arrived on 12 December 1904.  Under the supervision of naval architect Arthur L. Busch, the imported Hollands were re-assembled, and the first submersibles were ready for combat operations by August 1905, but hostilities were nearing the end by that date, and no submarines saw action during the war.
Meanwhile, the Imperial Russian Navy (IRN) purchased German constructed submersibles built by the Germaniawerft shipyards out of Kiel. In 1903, Germany successfully completed its first fully functional engine-powered submarine, Forelle (Trout),  It was sold to Russia in 1904 and shipped via the Trans-Siberian Railway to the combat zone during the Russo-Japanese War. 
Due to the naval blockade of Port Arthur, Russia sent their remaining submarines to Vladivostok, and by the end of 1904, seven subs were based there. On 1 January 1905, the IRN created the world's first operational submarine fleet around these seven submarines. The first combat patrol by the newly created IRN submarine fleet occurred on 14 February 1905, and was carried out by Delfin and Som, with each patrol normally lasting about 24 hours. Som first made contact with the enemy on 29 April, when it was fired upon by IJN torpedo boats, which withdrew shortly after opening fire and resulting in no casualties or damage to either combatant. A second contact occurred on 1 July 1905 in the Tartar Strait when two IJN torpedo boats spotted the IRN sub Keta. Unable to submerge quickly enough, [ clarification needed ] Keta was unable to obtain a proper firing position, and both combatants broke contact. 
World War I Edit
The first time military submarines had significant impact on a war was in World War I. Forces such as the U-boats of Germany operated against Allied commerce (Handelskrieg) the submarine's ability to function as a practical war machine relied on new tactics, their numbers, and submarine technologies such as combination diesel/electric power system that had been developed in the preceding years. More like submersible ships than the submarines of today, submarines operated primarily on the surface using standard engines, submerging occasionally to attack under battery power. They were roughly triangular in cross-section, with a distinct keel, to control rolling while surfaced, and a distinct bow. 
Shortly before the outbreak of World War I, submarines were employed by the Italian Regia Marina during the Italo-Turkish War without seeing any naval action, and by the Greek Navy during the Balkan Wars, where notably the French-built Delfin became the first such vessel to launch a torpedo against an enemy ship (albeit unsuccessfully).
At the start of the war, Germany had 48 submarines in service or under construction, with 29 operational. These included vessels of the diesel-engined U-19 class with the range (5,000 miles) and speed (eight knots) to operate effectively around the entire British coast.  Initially, Germany followed the international "Prize Rules", which required a ship's crew to be allowed to leave before sinking their ship. The U-boats saw action in the First Battle of the Atlantic.
After the British ordered transport ships to act as auxiliary cruisers, the German navy adopted unrestricted submarine warfare, [ citation needed ] generally giving no warning of an attack. During the war, 360 submarines were built, but 178 were lost. The rest were surrendered at the end of the war. A German U-boat sunk RMS Lusitania and is often cited among the reasons for the entry of the United States into the war. 
In August 1914, a flotilla of ten U-boats sailed from their base in Heligoland to attack Royal Navy warships in the North Sea in the first submarine war patrol in history.  Their aim was to sink capital ships of the British Grand Fleet, and so reduce the Grand Fleet's numerical superiority over the German High Seas Fleet. Depending more on luck than strategy, the first sortie was not a success. Only one attack was carried out, when U-15 fired a torpedo (which missed) at HMS Monarch, while two of the ten U-boats were lost. The SM U-9 had better luck. On 22 September 1914 while patrolling the Broad Fourteens, a region of the southern North Sea, U-9 found three obsolescent British Cressy-class armoured cruisers (HMS Aboukir, Hogue, and Cressy), which were assigned to prevent German surface vessels from entering the eastern end of the English Channel. The U-9 fired all six of its torpedoes, reloading while submerged, and sank the three cruisers in less than an hour.
The British had 77 operational submarines at the beginning of the war, with 15 under construction. The main type was the E-class, but several experimental designs were built, including the K-class, which had a reputation for bad luck, [ citation needed ] and the M-class, which had a large deck-mounted gun. The R-class was the first boat designed to attack other submarines. British submarines operated in the Baltic, North Sea and Atlantic, as well as in the Mediterranean and Black Sea. Over 50 were lost from various causes during the war.
France had 62 submarines at the beginning of the war, in 14 different classes. They operated mainly in the Mediterranean in the course of the war, 12 were lost. The Russians started the war with 58 submarines in service or under construction. The main class was the "Bars" with 24 boats. Twenty-four submarines were lost during the war.
World War II Edit
Although Germany was banned from having submarines in the Treaty of Versailles, construction started in secret during the 1930s. When this became known, the Anglo-German Naval Agreement of 1936 allowed Germany to achieve parity in submarines with Britain.
Germany started the war with only 65 submarines, with 21 at sea when war broke out. Germany soon built the largest submarine fleet during World War II. Due to the Treaty of Versailles limiting the surface navy, the rebuilding of the German surface forces had only begun in earnest a year before the outbreak of World War II. Having no hope of defeating the vastly superior Royal Navy decisively in a surface battle, the German High Command planned on fighting a campaign of "Guerre de course" (Merchant warfare), and immediately stopped all construction on capital surface ships, save the nearly completed Bismarck-class battleships and two cruisers, and switched the resources to submarines, which could be built more quickly. Though it took most of 1940 to expand production facilities and to start mass production, more than a thousand submarines were built by the end of the war.
Germany used submarines to devastating effect in World War II during the Battle of the Atlantic, attempting but ultimately failing to cut off Britain's supply routes by sinking more ships than Britain could replace. The supply lines were vital to Britain for food and industry, as well as armaments from Canada and the United States. Although the U-boats had been updated in the intervening years, the major innovation was improved communications, encrypted using the famous Enigma cipher machine. This allowed for mass-attack tactics or "wolfpacks" (Rudel), but was also ultimately the U-boats' downfall.
After putting to sea, the U-boats operated mostly on their own trying to find convoys in areas assigned to them by the High Command. If a convoy was found, the submarine did not attack immediately, but shadowed the convoy and radioed to the German Command to allow other submarines in the area to find the convoy. The submarines were then grouped into a larger striking force and attacked the convoy simultaneously, preferably at night while surfaced to avoid the ASDIC.
During the first few years of World War II, the Ubootwaffe ("U-boat force") scored unprecedented success with these tactics ("First Happy Time"), but were too few to have any decisive success. By the spring of 1943, German U-boat construction was at full capacity, but this was more than nullified by increased numbers of convoy escorts and aircraft, as well as technical advances like radar and sonar. High Frequency Direction Finding (HF/DF, known as Huff-Duff) and Ultra allowed the Allies to route convoys around wolfpacks when they detected radio transmissions from trailing boats. The results were devastating: from March to July of that year, over 130 U-boats were lost, 41 in May alone. Concurrent Allied losses dropped dramatically, from 750,000 tons in March to 188,000 in July. Although the Battle of the Atlantic continued to the last day of the war, the U-boat arm was unable to stem the tide of personnel and supplies, paving the way for Operation Torch, Operation Husky, and ultimately, D-Day. Winston Churchill wrote the U-boat "peril" was the only thing to ever give him cause to doubt eventual Allied victory.
By the end of the war, almost 3,000 Allied ships (175 warships, 2,825 merchantmen) were sunk by U-boats.  Of the 40,000 men in the U-boat service, 28,000 (70%) lost their lives.
The Germans built some novel submarine designs, including the Type XVII, which used hydrogen peroxide in a Walther turbine (named for its designer, Dr Hellmuth Walther) for propulsion. They also produced the Type XXII, which had a large battery and mechanical torpedo handling.
Italy had 116 submarines in service at the start of the war, with 24 different classes. These operated mainly in the Mediterranean theatre. Some were sent to a base at Bordeaux in Occupied France. A flotilla of several submarines also operated out of the Eritrean colonial port of Massawa.
Italian designs proved to be unsuitable for use in the Atlantic Ocean. Italian midget submarines were used in attacks against British shipping near the port of Gibraltar.
The Royal Navy Submarine Service had 70 operational submarines in 1939. Three classes were selected for mass production, the seagoing S-class and the oceangoing T-class, as well as the coastal U-class. All of these classes were built in large numbers during the war. 
The French submarine fleet consisted of over 70 vessels (with some under construction) at the beginning of the war.  After the Fall of France, the French-German Armistice required the return of all French submarines to German-controlled ports in France. Some of these submarines were forcibly seized by British forces.
The main operating theatres for British submarines were off the coast of Norway, in the Mediterranean, where a flotilla of submarines successfully disrupted the Axis replenishment route to North Africa from their base in Malta, as well as in the North Sea. As Germany was a Continental power, there was little opportunity for the British to sink German shipping in this theatre of the Atlantic.
From 1940, U-class submarines were stationed at Malta, to interdict enemy supplies bound for North Africa. Over a period of three years, this force sank over 1 million tons of shipping, and fatally undermined the attempts of the German High Command to adequately support General Erwin Rommel. Rommel's Chief of Staff, Fritz Bayerlein conceded that "We would have taken Alexandria and reached the Suez Canal, if it had not been for the work of your submarines". 45 vessels were lost during this campaign, and five Victoria Crosses were awarded to submariners serving in this theatre. 
In addition, British submarines attacked Japanese shipping in the Far East, during the Pacific campaign.  The Eastern Fleet was responsible for submarine operations in the Bay of Bengal, Strait of Malacca as far as Singapore, and the western coast of Sumatra to the Equator. Few large Japanese cargo ships operated in this area, and the British submarines' main targets were small craft operating in inshore waters.  The submarines were deployed to conduct reconnaissance, interdict Japanese supplies travelling to Burma, and attack U-boats operating from Penang. The Eastern Fleet's submarine force continued to expand during 1944, and by October 1944 had sunk a cruiser, three submarines, six small naval vessels, 40,000 long tons (41,000 t) of merchant ships, and nearly 100 small vessels.  In this theatre, the only documented instance of a submarine sinking another submarine while both were submerged occurred. HMS Venturer engaged the U864 and the Venturer crew manually computed a successful firing solution against a three-dimensionally maneuvering target using techniques which became the basis of modern torpedo computer targeting systems.
By March 1945, British boats had gained control of the Strait of Malacca, preventing any supplies from reaching the Japanese forces in Burma by sea. By this time, there were few large Japanese ships in the region, and the submarines mainly operated against small ships which they attacked with their deck guns. The submarine HMS Trenchant torpedoed and sank the heavy cruiser Ashigara in the Bangka Strait, taking down some 1,200 Japanese army troops. Three British submarines (HMS Stonehenge, Stratagem, and Porpoise) were sunk by the Japanese during the war. 
Japan had the most varied fleet of submarines of World War II, including manned torpedoes (Kaiten), midget submarines (Ko-hyoteki, Kairyu), medium-range submarines, purpose-built supply submarines (many for use by the Army), long-range fleet submarines (many of which carried an aircraft), submarines with the highest submerged speeds of the conflict (Sentaka I-200), and submarines that could carry multiple aircraft (WWII's largest submarine, the Sentoku I-400). These submarines were also equipped with the most advanced torpedo of the conflict, the oxygen-propelled Type 95 (what U.S. historian Samuel E. Morison postwar called "Long Lance").
Overall, despite their technical prowess, Japanese submarines – having been incorporated into the Imperial Navy's war plan of "Guerre D' Escadre" (Fleet Warfare), in contrast to Germany's war plan of "Guerre De Course" – were relatively unsuccessful. Japanese submarines were primarily used in offensive roles against warships, which were fast, maneuverable and well-defended compared to merchant ships. In 1942, Japanese submarines sank two fleet aircraft carriers, one cruiser, and several destroyers and other warships, and damaged many others, including two battleships. They were not able to sustain these results afterward, as Allied fleets were reinforced and became better organized. By the end of the war, submarines were instead often used to transport supplies to island garrisons. During the war, Japan managed to sink about 1 million tons of merchant shipping (184 ships), compared to 1.5 million tons for Great Britain (493 ships), 4.65 million tons for the U.S. (1,079 ships) and 14.3 million tons for Germany (2,840 ships).
Early models were not very maneuverable underwater, could not dive very deep, and lacked radar. Later in the war, units that were fitted with radar were in some instances sunk due to the ability of U.S. radar sets to detect their emissions. For example, Batfish (SS-310) sank three such equipped submarines in the span of four days. After the war, several of Japan's most original submarines were sent to Hawaii for inspection in "Operation Road's End" (I-400, I-401, I-201 and I-203) before being scuttled by the U.S. Navy in 1946, when the Soviets demanded access to the submarines as well.
United States Edit
After the attack on Pearl Harbor, many of the U.S. Navy's front-line Pacific Fleet surface ships were destroyed or severely damaged. The submarines survived the attack and carried the war to the enemy. Lacking support vessels, the submarines were asked to independently hunt and destroy Japanese ships and submarines. They did so very effectively. [ citation needed ]
During World War II, the submarine force was the most effective anti-ship and anti-submarine weapon in the entire American arsenal. Submarines, though only about 2 percent of the U.S. Navy, destroyed over 30 percent of the Japanese Navy, including 8 aircraft carriers, 1 battleship and 11 cruisers. U.S. submarines also destroyed over 60 percent of the Japanese merchant fleet, crippling Japan's ability to supply its military forces and industrial war effort. Allied submarines in the Pacific War destroyed more Japanese shipping than all other weapons combined. This feat was considerably aided by the Imperial Japanese Navy's failure to provide adequate escort forces for the nation's merchant fleet.
Whereas Japanese submarine torpedoes of the war are considered the best, those of U.S. Navy are considered the worst. For example, the U.S. Mark 14 torpedo typically ran ten feet too deep and was tipped with a Mk VI exploder, with both magnetic influence and contact features, neither reliable. The faulty depth control mechanism of the Mark 14 was corrected in August 1942, but field trials for the exploders were not ordered until mid-1943, when tests in Hawaii and Australia confirmed the flaws. In addition, the Mark 14 sometimes suffered circular runs, which sank at least one U.S. submarine, Tullibee.  Fully operational Mark 14 torpedoes were not put into service until September 1943. The Mark 15 torpedo used by U.S. surface combatants had the same Mk VI exploder and was not fixed until late 1943. One attempt to correct the problems resulted in a wakeless, electric torpedo (the Mark 18) being placed in submarine service. Tang was lost to a circular run by one of these torpedoes.  Given the prevalence of circular runs, there were probably other losses among boats which simply disappeared. 
During World War II, 314 submarines served in the United States Navy, of which nearly 260 were deployed to the Pacific.  On 7 December 1941, 111 boats were in commission and 203 submarines from the Gato, Balao, and Tench classes were commissioned during the war. During the war, 52 US submarines were lost to all causes, with 48 directly due to hostilities  3,505   sailors were lost, the highest percentage killed in action of any US service arm in World War II. U.S. submarines sank 1,560 enemy vessels,  a total tonnage of 5.3 million tons (55% of the total sunk),  including 8 aircraft carriers, a battleship, three heavy cruisers, and over 200 other warships, and damaged several other ships including the battleships Yamato (badly damaged by USS Skate (SS-305) ) and Musashi (damaged by USS Tunny (SS-282) ).  In addition, the Japanese merchant marine lost 16,200 sailors killed and 53,400 wounded, of some 122,000 at the start of the war, due to submarines. 
During the Cold War, the United States and the Soviet Union maintained large submarine fleets that engaged in cat-and-mouse games. This continues today, [ when? ] on a much-reduced scale. The Soviet Union suffered the loss of at least four submarines during this period: K-129 was lost in 1968 (which the CIA attempted to retrieve from the ocean floor with the Howard Hughes-designed ship named Glomar Explorer), K-8 in 1970, K -219 in 1986 (subject of the film Hostile Waters), and Komsomolets (the only Mike class submarine) in 1989 (which held a depth record among the military submarines—1,000 m, or 1,300 m according to the article K-278). Many other Soviet subs, such as K-19 (first Soviet nuclear submarine, and first Soviet sub at North Pole) were badly damaged by fire or radiation leaks. The United States lost two nuclear submarines during this time: USS Thresher and Scorpion. The Thresher was lost due to equipment failure, and the exact cause of the loss of the Scorpion is not known.
The sinking of PNS Ghazi in the Indo-Pakistani War of 1971 was the first submarine casualty in the South Asian region.
The United Kingdom employed nuclear-powered submarines against Argentina during the 1982 Falklands War. The sinking of the cruiser ARA General Belgrano by HMS Conqueror was the first sinking by a nuclear-powered submarine in war. During this conflict, the conventional Argentinian submarine ARA Santa Fé was disabled by a Sea Skua missile, and the ARA San Luis claimed to have made unsuccessful attacks on the British fleet. [ citation needed ]
There have been a number of accidental sinkings, but also some collisions between submarines. Up to August 1914, there were 68 submarine accidents. There were 23 collisions, 7 battery gas explosions, 12 gasoline explosions, and 13 sinkings due to hull openings not being closed. HMS Affray was lost in the English Channel in 1951 due to the snort mast fracturing and USS Thresher in 1963 due to a pipe weld failure during a test dive. Many other scenarios have been proven to be probable causes of sinking, most notably a battery malfunction causing a torpedo to detonate internally, and the loss of the Russian Kursk on 12 August 2000 probably due to a torpedo explosion. An example of the latter was the incident between the Russian K-276 and the USS Baton Rouge in February 1992.
Since 2000, there have been 9 major naval incidents involving submarines. There were three Russian submarine incidents, in two of which the submarines in question were lost, along with three United States submarine incidents, one Chinese incident, one Canadian, and one Australian incident. In August 2005, AS-28, a Russian Priz-class rescue submarine, was trapped by cables and/or nets off of Petropavlovsk, and saved when a British ROV cut them free in a massive international effort.
The Law of Maritime Neutrality and Submarine Cables
In an era of great power competition in which states seek to avoid “taking sides,” the international law of neutrality deserves greater attention. Information technology is the contemporary currency of power and the global network of over 420 submarine cables spanning some 700,000 miles is the information superhighway used for sharing 97 percent of international communications. During armed conflict, belligerents could degrade, damage, or sever submarine cables, or use them to launch cyberattacks against their enemy. These activities invariably will affect the economic and military communications of neutral states. To what extent may belligerent states damage, destroy, or use submarine cables owned or operated by neutral states to prosecute the war effort? This question lies at the intersection of three areas of law: the peacetime law of the sea, the law governing submarine cables, and the law of naval warfare, including the law of maritime neutrality. There are few restrictions on using or destroying neutral submarine cables in the law of naval warfare, which is lex specialis, and prevails as against the other two bodies of law during armed conflict. Belligerents may lawfully use the entire global network of submarine cables as a domain of virtual warfare without any material restraint from the law of neutrality. We may expect that belligerents will use, and even intentionally damage or cut neutral submarine cables.
This article first explores the peacetime law governing submarine cables. All states have the right to lay submarine cables on the high seas, as well as in the exclusive economic zone (EEZ) and continental shelves of coastal states. Next, the article focuses on the traditional maritime law of neutrality. This body of law applies during armed conflict and protects the rights of neutral states not party to the conflict, including the inviolability of submarine cables in their waters from physical attack by belligerents. This right, however, neither protects neutral cables lying outside neutral territorial waters from destruction by belligerents, nor prevents belligerents from using neutral cable infrastructure for cyberattacks against another belligerent. The automatic routing of cable traffic in today’s global submarine cable systems means that belligerents are unable to avoid neutral cables. At the same time, neutral states are absolved of their traditional obligation under the law of neutrality to ensure that their cables are not (mis)used by a belligerent. This article concludes that the technology of the global cable system, and customary law reflected in state practice, suggest that belligerent states would use or even destroy neutral submarine cables during armed conflict.
Law Governing Submarine Cables
Submarine cables wind through the seabed of the oceans and connect to landing stations on the beach. In peacetime, this infrastructure is protected from accidental or purposeful damage or destruction by the 1884 Convention for the Protection of Submarine Cables. The treaty states in article 15, however, that it does not limit belligerent rights during armed conflict. The operation of submarine cables in peacetime is also regulated by the 1982 United Nations Convention on the Law of the Sea (UNCLOS). States may lay cables in the EEZ and on the continental shelves of coastal states in accordance with articles 58(1) and 79, subject to the duty to exercise “due regard” for the resource rights of the host coastal states, as set forth in article 56. In these areas coastal states may adopt “reasonable measures” concerning foreign cables to protect its right to develop seabed mineral resources or to protect the marine environment, under article 79(2). States also may lay cables on the deep seabed beyond national jurisdiction under articles 87(1)(c) and 112. During armed conflict, however, the lex specialis regime of the law of naval warfare suspends UNCLOS among the belligerents and it modifies the relationship between belligerent states and neutral states.
The Law of Maritime Neutrality
Neutral states are those that have elected not to take part in an armed conflict and instead seek to maintain friendly, impartial relations with all states. The law of neutrality regulates the relationship between states that are party to a conflict and those that are not engaged in armed conflict. Neutral states strive to balance two conflicting interests: the right of belligerents to prosecute the war effort by isolating the enemy and destroying opposing armed forces, and the right of neutral states to be free from the adverse effects of armed conflicts to which they are not a party. As President Thomas Jefferson decreed in 1793 as French warships sought refuge in American ports during the war between revolutionary France and the first coalition, “the law of nations and the rules of neutrality forbid” taking sides.
The law of neutrality largely has focused on the right of neutral states on the high seas to engage in trade with one another, and separately, with belligerent states (except for contraband), as set out in the British Declaration on Neutrals and Letters of Marque of 28 March 1854 and the 1856 Paris Declaration Respecting Maritime Law. These provisions were further codified in article 6 of the U.S.-U.K. 1871 Washington Treaty. Neutral states have the right to engage in commerce, protected from the worst effects of armed conflict to which they are not a party.
Neutral territory is inviolable by belligerents under article 1 of the 1907 Hague Convention V. At sea, neutral space extends to the waters under the sovereignty of coastal states, including ports, internal waters, and the territorial sea of a state in accordance with articles 2 and 5 of Hague Convention XIII. Similarly, article 3 of the 1928 Convention on Maritime Neutrality requires that belligerents shall “refrain from acts of war” in neutral waters. This rule extends logically to archipelagic waters under Part IV of UNCLOS, as recognised in Part II, rules 23 to 30, of the San Remo Manual on International Law Applicable to Armed Conflict at Sea and para. 1.1 of the Helsinki Principles on the Law of Maritime Neutrality. Belligerent warships and auxiliaries may enter neutral territorial seas for mere transit but may not conduct operations in excess of simple innocent passage, archipelagic sea lanes passage, or transit passage through straits, as appropriate.
Belligerent states are forbidden from using neutral waters as a base of naval operations against the enemy. This proscription includes using neutral waters to refuel, resupply, repair, or rearm warships (beyond what is minimally required to get underway) in accordance with article 6 of Hague XIII, and belligerent warships may not remain in neutral waters longer than twenty-four hours under article 12, as well as article 5 of the 1928 Inter-American Convention on Maritime Neutrality.
Article 5 of Hague XIII prohibits belligerents from erecting on neutral territory “wireless telegraphy stations or any apparatus” used in military communications with “belligerent forces on land or sea.” This rule is amplified in article 4 of the Inter-American Convention: belligerents may not install in neutral waters “radio-telegraph stations or any other apparatus” to communicate with military forces, or to “make use” of such installations established before the war and “which have not been opened to the public.” These rules on the neutral inviolability of the physical domain of waters under coastal state sovereignty also apply to submarine cables physically present in those areas. The law of neutrality has always been complex – even unsettled – and submarine cables makes analysis even more challenging.
“Necessities of War”
Submarine cables that lie on the continental shelf in the internal waters, archipelagic waters, or territorial sea of a coastal state are under the sovereignty of the coastal state and are physically inviolable during armed conflict. During the Spanish-American war, the United States set the precedent for the belligerent right to cut neutral cables serving the enemy that lie outside neutral waters. On 1 May 1898, Commodore Dewey entered Manila Bay and destroyed or captured the Spanish fleet. The following day, he cut the Manila-Hong Kong cable owned by a British company and laid down under Spanish concession. Afterward, First Lord of the Treasury Balfour remarked in parliament that article 15 of the 1884 Treaty recognised the right of belligerents to cut cables used by the enemy. The United States also severed cables in Cuba and Puerto Rico, which were also owned by a British company.
In 1902, a table-top exercise published in volume 2 of International Law Studies at the U.S. Naval War College concluded that belligerent states acting on the high seas could interrupt or cut submarine cables between belligerents and neutrals “if the necessities of war require,” although cables connecting neutral states only were inviolable. Similarly, in article 54 of the 1907 Hague IV Regulations, cables connecting an occupied territory with a neutral territory are protected from seizure or damage “except in the case of absolute necessity.” The exception seems to swallow the rule. The U.S. actions during the Spanish-American war resulted in a U.S.-U.K. arbitration tribunal in 1923, the “Eastern Extension Case,” that considered compensation for British companies that owned the cables. The tribunal denied compensation, ruling that cutting the cables was consistent with the law of naval warfare and “fully justified.” After World War II, in commenting on attacks against submarine cables during time of war, C. John Colombos declared in § 471 of his 1951 classic treatise, “there do not appear to be any [rules] which are clearly discernible.” The more complicated operation and administration of submarine cables in the cyber era magnifies uncertainty in applying the neutrality law.
Not everyone would agree today with the holding in the Eastern Extension Case, which permitted a belligerent to cut a cable outside neutral territory. Rule 150 of the Tallinn Manual 2.0 on the International Law Applicable to Cyber Operations, for example, asserts that the exercise of belligerent rights by cyber means “directed against” neutral submarine infrastructure, such as submarine cables, is prohibited. This proscription applies to cables inside the territorial waters of the coastal state, as well as those owned by companies of the neutral state that span the globe. Furthermore rule 151 of the Tallinn Manual 2.0 states that “the exercise of belligerent rights by cyber means” are prohibited in neutral territory. This approach incorrectly analogises cyber data as akin to physically transporting munitions or supplies of war through a neutral power, which is a violation of article 2 of Hague V.
Information packets, however, like radio or sound waves, merely propagate energy and therefore cannot not be analogised to physically violating neutral territory. The law of neutrality was developed based on actions in the physical domain – the sanctity of neutral waters, for example. Submarine cables, while consisting of a physical infrastructure, serve as a medium of transmission and operate much like the airspace, within which radio waves propagate at will. Travel by ship through neutral waters implicates the law of neutrality, so too does flight in national airspace. But broadcasting radio waves through neutral national airspace does not by itself affect state sovereignty in the same way, since it is not a tangible physical activity. Likewise, submarine cables located in neutral states are themselves physically inviolable, but their usage as information conduits are not protected during armed conflict. Under this view, belligerents may utilise submarine cables as part of their cyberattack against an enemy. Indeed, the nature of submarine cables today means there is no alternative to this view because submarine cables are no longer bi-polar, in which data serves only the two states physically connected. Implementation of the Tallinn Manual 2.0 rules appears to presume a level of control required by belligerents to avoid cables lying in neutral waters or neutral cables on the deep seabed that almost certainly is unrealistic.
The Russian government’s apparent loss of control over Notpetya, the most devastating cyberattack in history, is a case in point. It suggests that it is difficult to create a discriminate cyber weapon. Once unleashed, it appears that because of the nature of the submarine cable network that it will be impossible to keep a cyber weapon out of neutral territory or off neutral cables. The reasons why relate to the way submarine cables operate today. One hundred years ago submarine cables were bipolar, connecting country X to country Y. It was simple to conduct an analysis of whether a neutral state was affected by cutting a cable.
The Global Submarine Cable System
Today, however, submarine cables generally are owned and operated by multinational consortia consisting of from four to as many as forty stakeholders, each with a percentage ownership stake in the cable. Google, for example, has partial stakes in more than a dozen submarine cables. These ownership consortia are responsible for construction and maintenance of the cable based on a divided percent of the capacity. The entities that own the cables typically are based in tax havens, such as Bermuda, even if the actual ownership is by a company in the United States or Germany. There is no global registry of ownership for submarine cables, so it is difficult, perhaps impossible, to identify the actual owners. The cable obtains a landing license in each state that it physically touches, and the landing state likely would obtain information on all the owners. But, here it gets even more complicated because the owners often sublease part or all their stake to another company located in another state, and this subdivision, called an indefeasible right of use, is usually not reported subsequently to landing states. Thus, states with an interest in the cable would not be known to either landing states or belligerent states that propose to use the cable during hostilities.
To make matters even more complex, it is likely impossible for a belligerent state targeting a submarine cable to be certain of the impact on any neutral state, or neutral states generally, because submarine cable traffic is automatically re-routed in a fraction of a second in the event of a cable casualty or disruption. This split-second re-routing is negotiated in advance under mutual restoration agreements with multiple cable operators. All neutral states connected to the cable network must be factored into the belligerent state’s targeting analysis.
Ninety-eight percent of cables are commercial, non-government lines. Military information packets sent by a belligerent state are indistinguishable from ordinary Internet traffic and the specific pathways of information through submarine cables is unpredictable and uncontrollable. Attempts to establish a legal rule that precludes every belligerent use of neutral commercial submarine cables would be nugatory. While the 1902 Naval War College study and the Eastern Extension Case concluded that belligerents could damage or cut neutral submarine cables “if the necessities of war require,” the Tallinn Manual is more restrictive, stating that such attacks are prohibited if the belligerent has knowledge such action would generate foreseeable spillover effects on the neutral state. The 1923 arbitration sets the standard. Belligerents acting pursuant to military necessity may entirely disrupt or even cut the cable despite its effect on neutral states. Between the more restrictive Tallinn Manual 2.0 commentary and the permissive 1923 arbitration, the arbitration is the more realistic and compelling standard. In the exigencies of war, belligerents will utilise cables and conduct cyberattacks through them, particularly when the law is less than certain. The 1923 arbitration and the practicalities driven by cable operations today suggest that belligerents may resort to using – or even cutting – submarine cables as a method of naval warfare. In effect, the virtual cyberspace within submarine cables, like the airwaves, constitutes a global electromagnetic domain that is open to belligerents. Neither the black letter law nor the actual technology supports more aspirational protections of neutral states. What about the ability of neutral states to fulfil their obligations of impartiality?
Duties of Neutral States on the Use of their Cables
The rights of neutral states concerning submarine cables have been diminished in law, aided by the impracticality of discerning among users and cables and the ubiquity of the global Internet. At the same time, these factors also have absolved neutral states of their traditional duties of neutrality in armed conflict when it comes to submarine cables.
Rule 152 of the Tallinn Manual 2.0 suggests that neutral states have a due diligence requirement to ensure their submarine cables are not utilised for belligerent purposes. Yet the amorphous nature of the electromagnetic data traveling through submarine cables, while exposing neutral states to belligerent activity, also mitigates their duty to ensure belligerents do not use their cables. Neutral states have an obligation to ensure that belligerents do not use their territory or waters under their sovereignty to prosecute the war effort. The British Wireless Telegraphy (Foreign Ships) Regulations of 1908, for example, authorised the postmaster general and the Admiralty to “control transmissions of messages by wireless telegraphy” by foreign ships in the territorial waters. The United States had the same policy, which rankled the Germany and Austria during World War I, since there was no restriction on submarine cable messages. The U.S. rationale to distinguish censoring radio transmissions in the territorial sea, but not submarine cable messages, was that radio waves broadcast in the open cannot be interrupted and may be received and utilised by anyone – including belligerent warships on the high seas, making the neutral territory or territorial sea from where they were broadcast a base of naval operations, an unneutral act. At that time, submarine cables in a neutral state, on the other hand, could not be used as a means of direct communication with belligerent warships on the high seas. Furthermore, undersea cables may be cut by belligerents, as the German cruiser SMS Nürnberg did in its 1914 attack on the cable relay station at Fanning Island in the central Pacific Ocean.
Article 8 of Hague V states that neutral powers need not “forbid or restrict the use on behalf of the belligerents of telegraph or telephone cables or of wireless telegraphy apparatus belonging to it or to companies or private individuals.” Utilising submarine cables, like telephone and wireless transmissions, do not involve physical entry into the neutral state. That provision indicates that neutral states are not under an obligation to ferret out and stop the (mis)use of their submarine cables by belligerent states, and by not doing so, they do not jeopardise their neutral status. Regardless of either approach, however, if a neutral state restricts or prohibits belligerents from using its submarine cables it must do so in a manner that is impartial to all parties to a conflict.
Belligerents Likely will Use Neutral Cables
In conclusion, the traditional law of neutrality uneasily covers the case of submarine cables. While it is clear that belligerent states are not permitted in situ to use submarine cables located in the territory or territorial sea, straits, or archipelagic waters of a coastal state, this infrastructure may be used virtually, despite the electromagnetic data traversing neutral cables on the high seas, or indeed in the territory of the neutral coastal state. This rule, consistent with the 1923 US-UK arbitration, is more permissive than the majority view of the Tallinn Manual 2.0 commentary. It is also more realistic since states engaged in armed conflict may determine they have a compelling military need to use (or to cut) submarine cables. These legal findings have great implications for neutral states and submarine cables during armed conflict. Not only may neutral states have very little or no expectation that belligerents will refrain from using their submarine cables, it is also largely impractical to expect neutral states to attempt to prevent such use.
- A neutral country in a particular war, is a sovereign state which refrains from joining either side of the conflict and adheres to the principle of the Law of Neutrality under International Law. Although countries have historically often declared themselves as neutral at the outbreak of war, there is no obligation for them to do so.  The rights and duties of a neutral power are defined in Sections 5  and 13  of the Hague Convention of 1907.
- A permanently neutral power is a sovereign state which is bound by international treaty, or by its own declaration, to be neutral towards the belligerents of all future wars. An example of a permanently neutral power is Switzerland. The concept of neutrality in war is narrowly defined and puts specific constraints on the neutral party in return for the internationally recognized right to remain neutral.
- Neutralism or a "neutralist policy" is a foreign policy position wherein a state intends to remain neutral in future wars. A sovereign state that reserves the right to become a belligerent if attacked by a party to the war is in a condition of armed neutrality.
- A non-belligerent state is one that indirectly participates in a war, politically and/or materially helping one side of the conflict and thus not participating militarily. For example, it may allow its territory to be used for the war effort. Contrary to neutrality, this term is not defined under International Law.
Belligerents may not invade neutral territory,  and a neutral power's resisting any such attempt does not compromise its neutrality. 
A neutral power must intern belligerent troops who reach its territory,  but not escaped prisoners of war.  Belligerent armies may not recruit neutral citizens,  but they may go abroad to enlist.  Belligerent armies' personnel and materiel may not be transported across neutral territory,  but the wounded may be.  A neutral power may supply communication facilities to belligerents,  but not war materiel,  although it need not prevent export of such materiel. 
Belligerent naval vessels may use neutral ports for a maximum of 24 hours, though neutrals may impose different restrictions.  Exceptions are to make repairs—only the minimum necessary to put back to sea  —or if an opposing belligerent's vessel is already in port, in which case it must have a 24-hour head start.  A prize ship captured by a belligerent in the territorial waters of a neutral power must be surrendered by the belligerent to the neutral, which must intern its crew. 
Neutrality has been recognised in different ways, and sometimes involves a formal guarantor. For example, Austria has its neutrality guaranteed by its four former occupying powers, Switzerland by the signatories of the Congress of Vienna and Finland by the Soviet Union during the Cold War. The form of recognition varies, often by bilateral treaty (Finland), multilateral treaty (Austria) or a UN declaration (Turkmenistan). These treaties can in some ways be forced on a country (Austria's neutrality was insisted upon by the Soviet Union) but in other cases it is an active policy of the country concerned to respond to a geopolitical situation (Ireland in the Second World War). 
For the country concerned, the policy is usually codified beyond the treaty itself. Austria and Japan codify their neutrality in their constitutions, but they do so with different levels of detail. Some details of neutrality are left to be interpreted by the government while others are explicitly stated, for example Austria may not host any foreign bases and Japan cannot participate in foreign wars. Yet Sweden, lacking formal codification, was more flexible during the Second World War in allowing troops to pass through its territory. 
Armed neutrality is the posture of a state or group of states that has no alliance with either side of a war but asserts that it will defend itself against resulting incursions from any party.  This may include:
- Military preparedness without commitment, especially as the expressed policy of a neutral nation in wartime, and the readiness to counter with force an invasion of rights by any belligerent power. 
- Armed neutrality is a term used in international politics for the attitude of a state or group of states that makes no alliance with either side in a war. It is the condition of a neutral power during a war to hold itself ready to resist by force, any aggression of either belligerent. 
- Armed neutrality makes a seemingly-neutral state take up arms for protection to maintain its neutrality.
The term derives from the historic maritime neutrality of the First League of Armed Neutrality of the Nordic countries and Russia under the leadership of Catherine the Great, which was invented in the late 18th century but has since been used only to refer to countries' neutralities.  Sweden and Switzerland are independently of each other famed for their armed neutralities, which they maintained throughout both World War I and World War II.  The Swiss and the Swedes each have a long history of neutrality: they have not been in a state of war internationally since 1815 and 1814, respectively. They pursue, however, active foreign policies and are frequently involved in peace-building processes around the world.  According to Edwin Reischauer, "To be neutral you must be ready to be highly militarized, like Switzerland or Sweden." 
In contrast, other neutral states may abandon military power (examples of states doing this include Costa Rica and Liechtenstein) or reduce it, but rather uses it for the express purpose of home defense and the maintenance of its neutrality. But the lack of a military does not result in neutrality as countries such as Iceland replaced a standing military with a military guarantee from a stronger power.
Leagues of Armed Neutrality Edit
- The First League of Armed Neutrality was an alliance of minor naval powers organized in 1780 by Catherine II of Russia to protect neutral shipping in the War of American Independence.  The establishment of the First League of Armed Neutrality was viewed by Americans as a mark of Russian friendship and sympathy. This league had a lasting impact of Russian-American relations and the relations of those two powers and Britain. It was also the basis for international maritime law, which is still in effect.  In the field of political science, this is the first historical example of armed neutrality, however, scholars like Dr. Carl Kulsrud argue that the concept of armed neutrality was introduced even earlier. Within 90 years before the First League of Armed Neutrality was established, neutral powers had joined forces no less than three times. As early as 1613, Lubeck and Holland joined powers to continue their maritime exploration without the commitment of being involved in wartime struggles on the sea. 
- The Second League of Armed Neutrality was an effort to revive this during the French Revolutionary Wars.  It was an alliance with Denmark-Norway, Prussia, Sweden and Russia. It occurred during 1800 and 1801. The idea of this second league was to protect neutral shipping from the British Royal Navy. However, Britain took this as the alliance taking up sides with France, and attacked Denmark leading to the Battle of Copenhagen (1801) and the taking of Copenhagen by the British. The alliance was forced to withdraw from the league.
- A potential Third League of Armed Neutrality was discussed during the American Civil War, but was never realized. 
For many states, such as Ireland and Sweden, neutrality does not mean the absence of any foreign interventionism. Peacekeeping missions for the United Nations are seen as intertwined with it.  The Swiss electorate rejected a 1994 proposal to join UN peacekeeping operations. Despite this, 23 Swiss observers and police have been deployed around the world in UN projects. 
The legitimacy of whether some states are as neutral as they claim has been questioned in some circles, although this depends largely on a state's interpretation of its form of neutrality.
European Union Edit
There are five members of the European Union that still describe themselves as a neutral country in some form: Austria, Ireland, Finland, Malta and Sweden. With the development of the EU's Common Security and Defence Policy, the extent to which they are, or should be, neutral is debated. For example, former Finnish Prime Minister, Matti Vanhanen, on 5 July 2006, stated that Finland was no longer neutral:
"Mr Pflüger described Finland as neutral. I must correct him on that: Finland is a member of the EU. We were at one time a politically neutral country, during the time of the Iron Curtain. Now we are a member of the Union, part of this community of values, which has a common policy and, moreover, a common foreign policy." 
However, Finnish Prime Minister Juha Sipilä on 5 December 2017 still described the country as "militarily non-aligned" and that it should remain so.  Ireland, which sought guarantees for its neutrality in EU treaties, argues that its neutrality does not mean that Ireland should avoid engagement in international affairs such as peacekeeping operations. 
Since the enactment of the Lisbon Treaty, EU members are bound by TEU, Article 42.7, which obliges states to assist a fellow member that is the victim of armed aggression. It accords "an obligation of aid and assistance by all the means in [other member states'] power" but would "not prejudice the specific character of the security and defense policy of certain Member States" (neutral policies), allowing members to respond with non-military aid.
With the launch of Permanent Structured Cooperation (PESCO) in defense at the end of 2017, the EU's activity on military matters has increased. The policy was designed to be inclusive and allows states to opt in or out of specific forms of military cooperation. That has allowed most of the neutral states to participate, but opinions still vary. Some members of the Irish Parliament considered Ireland's joining PESCO as an abandonment of neutrality. It was passed with the government arguing that its opt-in nature allowed Ireland to "join elements of PESCO that were beneficial such as counter-terrorism, cybersecurity and peacekeeping. what we are not going to be doing is buying aircraft carriers and fighter jets". Malta, as of December 2017, is the only neutral state not to participate in PESCO. The Maltese government argued that it was going to wait and see how PESCO develops to see whether it would compromise Maltese neutrality. 
According to Ion Marandici, Moldova has chosen neutrality in order to avoid Russian security schemes and Russian military presence on its territory.  Even if the country is constitutionally neutral, some researchers argue that de facto this former Soviet republic never was neutral, because parts of the Russian 14th army are present at Bendery, a territory de facto not controlled by Moldovan government.  The same author suggests that one solution in order to avoid unnecessary contradictions and deepen at the same time the relations with NATO would be "to interpret the concept of permanent neutrality in a flexible manner".  Neutrality is a constant topic in Moldovan domestic politics. 
Neutrality during World War II Edit
|"Neutrality is a negative word. It does not express what America ought to feel. We are not trying to keep out of trouble we are trying to preserve the foundations on which peace may be rebuilt.”|
|— Woodrow Wilson|
Many countries made neutrality declarations during World War II. However, of the European states closest to the war, only Andorra, Ireland, Portugal, Spain, Sweden, Switzerland (with Liechtenstein), and Vatican (the Holy See) remained neutral to the end.
Their fulfillment to the letter of the rules of neutrality has been questioned: Ireland supplied important secret information to the Allies for instance, the date of D-Day was decided on the basis of incoming Atlantic weather information, some of it supplied by Ireland but kept from Germany. Ireland also secretly allowed Allied aircraft to use the Donegal Corridor, making it possible for British planes to attack German U-boats in the mid-Atlantic. On the other hand, both Axis and Allied pilots who crash landed in Ireland were interned. 
Sweden and Switzerland, surrounded by possessions and allies of Nazi Germany similarly made concessions to Nazi requests as well as to Allied requests.  Sweden was also involved in intelligence operations with the Allies, including listening stations in Sweden and espionage in Germany. Spain offered to join the war on the side of Nazi Germany in 1940, allowed Axis ships and submarines to use its ports, imported war materials for Germany, and sent a Spanish volunteer combat division to aid the Nazi war effort. Portugal officially stayed neutral, but actively supported both the Allies by providing overseas naval bases, and Germany by selling tungsten.
The United States was initially neutral and bound by the Neutrality Acts of 1936 not to sell war materials to belligerents. Once war broke out, US President Franklin Delano Roosevelt persuaded Congress to replace the act with the Cash and carry program that allowed the US to provide military aid to the allies, despite opposition from non-interventionist members.  The "Cash and carry" program was replaced in March 1941 by Lend-Lease, effectively ending the US pretense of neutrality.
Sweden also made concessions to the German Reich during the war to maintain its neutrality, the biggest concession was to let the 163rd German Infantry Division to be transferred from Norway to Finland by Swedish trains, to aid the Finns in the Continuation War. The decision caused a political "Midsummer Crisis" of 1941, about Sweden's neutrality.
Equally, Vatican City made various diplomatic concessions to the Axis and Allied powers alike, while still keeping to the rules of the law of neutrality. The Holy See has been criticized—but largely exonerated later—for its silence on moral issues of the war. 
Some countries may occasionally claim to be "neutral" but not comply with the internationally agreed upon definition of neutrality as listed above.
The History of Submarine Warfare
Sir Dig-A-Lot answered, “It is like an underwater vessel which is used as a mode of transport. It was used extensively in the World War 1.
In warfare, it is used to launch missile attacks on surface ships, submarines, for mine laying and even to launch a nuclear attack. They are also used for explorations, underwater pipelines and searching for gas.”
“Germany and Britain were in competition with each other about their naval strength. So much so, that Germany introduced unrestricted submarine warfare, which was, attacking all ships including unarmed civilian ships which would belong to neutral countries.
On May 7 1915, the German submarine attacked the British merchant ship Lusitania, that had civilians from many countries including the USA. The attack killed over 1000 people. After the United States of America criticised the attack, the Germans stopped for a while, because they feared that the USA would enter the war.
On February 1 1917, Germany resumed the attacks, in a bid to defeat the British fast. This cost them, as the USA formally entered the war against the Germans. However, Germany used submarines until the last months of the war, in the hope of winning through naval confrontation.”
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Did you know …
- The move from neutrality to war brought real changes in the United States. The government passed strict laws forbidding any words or actions that questioned the government's war aims, and it created a government agency, the Committee on Public Information, to produce propaganda promoting government policies.
- Wilson's decision to institute a military draft (required enrollment in the military for selected people) in 1917 was quite unpopular, even within the military. Many people believed that military drafts were incompatible with democracy. Despite these problems, the draft successfully built an army of nearly one million soldiers.
Why did Germany use submarine warfare?
The German naval tactic of WWI Germany retaliated by using its submarines to destroy neutral ships that were supplying the Allies. They were Germany's only weapon of advantage as Britain effectively blocked German ports to supplies. The goal was to starve Britain before the British blockade defeated Germany.
Secondly, how did submarines change warfare? Submarines changed the war because it was easier to attack enemies from under the water. As a result, Germany sank British ships. During WWI, German military had adopted a policy called "unrestricted submarine warfare". Therefore, submarines were allowed to attack non-military ships.
Also, what is the name of the submarines used by Germany for sea warfare?
For British merchant vessels operating during World War I, few things were so terrifying as the submarine. The German navy used the Unterseeboot, or U-boat, to sink 5,000 ships measuring more than 13 million gross register tons during the war.
What was the main result of Germany's use of unrestricted submarine warfare?
The main result of the Germany's use of unrestricted submarine warfare during world war 1 was that it led to the US entering the war agains Germany, since this caused the sinking of the Lusitania, which was carrying many Americans.