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A submarine is a specialized boat that travels under water, usually for military or scientific purposes. Most major navies of the world employ submarines. Submarines are also used for marine and freshwater science and for work at depths too great for human divers. U-boat is the abbreviation of Unterseeboot, the German name for German submarines (first commissioned in 1906). Another underwater device for use in underwater exploration and salvage is the diving bell.
In common usage, submarine normally connotes military submarine; vessels used for research or commercial purposes are usually called submersibles. Non-military submarines are usually much smaller than military submarines. A type called a bathysphere lacks self-propulsion. A predecessor of the bathysphere, the diving bell, consisted of a chamber, with an open bottom, lowered into the water.
Tourist submarines work mainly in tropical resort areas. In 1996, there were over fifty private submarines operating around the world, serving approximately two million passengers that year. Most of these submarines carried between twenty-five and fifty passengers at a time and sometimes made ten or more dives a day. In design, these submarines borrow mainly from research subs, having large windows for passengers' viewing and often placing significant mechanical systems outside the hull to conserve interior space. Nonetheless, even the seating aboard tourist submarines can be rather cramped. They are mainly battery-powered and very slow.
A fairly recent development, very small unmanned submarines called marine remotely operated vehicles are widely used today to work in water too deep or too dangerous for divers. For example, remotely operated vehicles (ROVs) repair offshore petroleum platforms and attach cables to sunken ships to hoist them. Such remotely operated vehicles are attached by a tether (a thick cable providing power and communications) to control center on a ship. Operators on the ship see video images sent back from the robot and may control its propellers and manipulator arm. The wreck of the Titanic was explored by such a vehicle, as well as a manned vessel.
There are probably more military submarines in operation than any other type of submarine, though it is difficult to obtain exact figures because navies are secretive about their submarine fleets.
Submarines are useful to a military because they can approach their attack victim without being detected, then strike at close range. A great deal of attention in the design of a submarine is devoted to making its travel through the water silent to prevent its detection by enemy ships and submarines.
Modern submarines are usually cigar-shaped. This design, officially called a "teardrop hull", was patterned after the bodies of whales. It significantly decreases the friction between the water and the sub, and allows the sub to go much faster than earlier designs. The USS Albacore was the first vessel to use a teardrop hull. With nuclear power they can remain submerged nearly all of the time, surfacing only rarely.
A raised tower on top of a submarine accommodates the length of the periscopes and electronics masts, which can include radio, radar, electronic warfare, and other systems. In the obsolete boat-shaped classes of submarines (see history, below), the control room, or conn, was located inside this tower, which was known as the conning tower. Since that time, however, conn has been located within the main body of the submarine, and the tower is more commonly called the sail today. In another interpretation, conning tower comes from the English verb to con, which means to navigate, indicating the presence of navigational systems in the conning tower. The conn should not be confused with the bridge, which is a small platform set into the top of the sail used for visual observation while running on the surface.
Modern submarines use an Inertial guidance system for navigation whilst submerged, however, drift error build up over time is unavoidable. To counter this, the global positioning system will be occasionally used to obtain an accurate position. The periscope is only used occasionally, since the range of visibility below the sea is short.
A typical military submarine has a crew of over one hundred. Their job is one of the most difficult assignments in the navy, for they must work in isolation for long periods, without much contact with their families, since submarines normally maintain radio silence to avoid detection. Operating a submarine is dangerous, even in peacetime; many submarines have been lost in accidents (see history, below).
Submarines have been in use for a long time, but as technology has improved, their role has changed drastically. The common feature has always been their stealth, cloaked by miles of ocean. Even with modern detection systems, submarines can still travel almost invisibly.
Military submarines come in two general types: ballistic-missile submarines and attack submarines. (Outside these categories may fall the many smaller midget submarines, used for sabotage, espionage and secretive transport. Note that North Korea's submarine fleet, estimated as the fourth-largest in the world in the 1990s, consists largely of smaller vessels. Also outside the two categories fall the World War II German milch cow submarines: submersible supply vessels.)
Ballistic missile submarines (or boomers, in American slang) carry nuclear weapons in the missiles for attacking strategic targets such as cities or missile silos anywhere in the world. They are universally nuclear-powered, to provide the greatest stealth and endurance (While there is no technical reason that nuclear missile submarines must have nuclear propulsion this choice has been universally adopted). They played an important part in Cold War mutual deterrence: since both the United States and the Soviet Union had the capability (or could contend to have) to heavily strike at the attacking nations should one attack the other, both nations were "deterred". The British Royal Navy possess a single class of four ballistic missile submarines known as the Vanguard-class. The RN's previous ballistic missile submarine class was the Resolution-class which also consisted of four boats. The Resolutions, named after battleships to convey the fact they were the new capital ships, were decommissioned upon the Vanguards entering service in the 1990s. The People's Republic of China also possesses one ballistic missile submarine (Xia class). The American George Washington-class "boomers" were named for "famous Americans" and the later Ohio class were named for states, with the exceptions that some of the "famous Americans" were foreigners and SSBN-730 gained the name of a Senator.
Submarines designed for the purpose of attacking merchant ships or other warships are known as attack or hunter-killer submarines. They typically carry torpedoes for attacking naval vessels. Today they generally carry cruise missiles for attacking land-based targets or shipping. The USSR also developed several types of missile attack submarine, which carried a heavy load of antisurface missiles, at a time when most attack submarines used torpedos only.
Attack submarines use a much wider variety of propulsion systems. The majority use the same diesel-electric combination developed early in the 20th century, many use nuclear power, and a growing number use some other form of air-independent propulsion such as fuel cells or Stirling engines. All of the attack submarines of the United States use nuclear power.
All American attack submarines (that had actual names rather than just alphanumeric designators) were named for "denizens of the deep" until the Los Angeles class, which are named for cities—with the exceptions of several named for politicians, and the new Seawolf class, which received the traditional name for the first, a state name for the second and a presidential name for the third.
The first modern submarines, capable of underwater ocean voyages were designed and built in France in the 1890s.
The first submarine for which there is reliable information that it was really built, is the one constructed in 1620 by Cornelius Jacobszoon Drebbel, a Dutchman in the service of James I. Its propulsion was by means of oars. The precise nature of the type is a matter of some controversy, some claiming it was merely a bell towed by a boat. There were two improved types, tested below the surface of the Thames between 1620 and 1624.
Though the first submersible vehicles were tools for exploring under water, it did not take long for inventors to recognize their military potential. The first military submarine was the Turtle, a hand-powered spherical contraption designed by American David Bushnell that accommodated a single man. During the American Revolutionary War, the Turtle attempted and failed to sink a British warship, the HMS Eagle in New York harbor on September 7, 1776.
In 1800, Robert Fulton demonstrated to the French, and then to the British, how to destroy ships with his human-powered submarine Nautilus using a mine, but none of the governments showed any interest.
During the American Civil War, the Union was the first to field a submarine. The USS Alligator was the first U.S. Navy sub and the first sub to feature compressed air or air filtration. It was the first submarine to carry a diver lock which allowed a diver to exit to plant electrically-detonated mines on enemy ships. Initially powered by oars, it was later converted to a screw-propeller. With a crew of 20, it was far larger than Confederate submarines. The Alligator was 47 feet (14.3 meters) long and about 4 feet (1.2 meters) in diameter. It was lost in a storm off Cape Hatteras on April 1, 1863 while uncrewed and under tow to its first combat deployment at Charleston.
The Confederate States of America fielded several human-powered submarines including the CSS Hunley. The first Confederate submarine was the 30-foot long 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 CSS Hunley was used for attacking the North's ships, which were blockading the South's seaports. The submarine had a long pole on the front, upon which was attached an explosive charge. The sub was to sneak up to an enemy vessel, attach the explosive, move away, and then detonate. 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 ocasion half the crew died and on the second, the entire eight-man crew perished. On February 18, 1864 the CSS Hunley sank the USS Housatonic in the Charleston Harbor, the first time a submarine successfully sank another ship. Hunley did not survive its maiden mission and was not a major factor in the war. Another Confederate submarine was lost on its maiden voyage in Lake Pontchartrain; it was found washed ashore in the 1870s and is now on display at the Louisiana State Museum.
The first mechanically powered submarine was the peroxide driven Ictineo II, launched in 1864 by Narcís Monturiol. This submarine was originally built to ease the harvest of coral.
In 1870, writer Jules Verne published the science fiction classic 20,000 Leagues under the Sea, which concerns the adventures of a maverick inventor in the Nautilus, a submarine more advanced than any that existed at that time. The fictional story inspired inventors to build more advanced submarines.
In 1879, a Manchester curate, the Reverend George Garrett built the steam-powered 'Resurgam' at Birkenhead. Garrett intended to demonstrate the 12 metre long vehicle to the British Navy at Portsmouth, but had mechanical problems, and while under tow the submarine was flooded and sank off North Wales.
The first submarine built in series, however, was human-powered. It was the submarine of the Polish inventor Stefan Drzewiecki—50 units were built in 1881 for Russian government. In 1884 the same inventor built an electric-powered submarine. In 1899, the French steam and electric submarine Narval introduced the classic twin-hull design, with an inner hull inside an outer hull.
The Irish inventor John Holland had better luck, and designed and built several quite successful gasoline- and electric powered submarines. Some of his vessels were purchased by the United States, the United Kingdom, and Japan, and commissioned into their navies.
The Spanish inventor Isaac Peral built a practical submarine in 1888, but despite of the success of the trials, the Spanish Navy scrapped the project.
Many more submarines were built subsequently by various inventors, but they were not to become effective weapons until the 20th century.
The first military submarines to see effective use were the U-boats of Germany, first introduced in the First Battle of the Atlantic in World War I. The innovation that made the U-boats practical war machines was their use of diesel. More like submersible ships than the submarines of today, U-boats operated primarily on the surface, submerging occasionally to attack. Thus, they were roughly triangular in cross-section, with a distinct keel, to control rolling while surfaced. The sinking of the ocean liner RMS Lusitania by a U-boat was a major factor in bringing the United States of America into the war.
Germany again put submarines to devastating effect against the merchant ships of the United Kingdom and the United States in the Second Battle of the Atlantic in World War II. Although the U-boats were improved, the main reason for their success was the introduction of mass-attack tactics called a pack (in German, Rudel) commonly traveled and fought together. (The term is often translated as "wolf-pack", but the German word does not specify wolves). Germany attempted to maintain a blockade against the United Kingdom, which because of its reliance on imports for food and industry was extremely vulnerable. Winston Churchill wrote that the U-boat threat was the only thing that ever gave him cause to doubt the Allies' eventual victory.
During World War II the Japanese intended their submarines to be scouts. The submarines were fast, large, could operate over 100 days and many carried an aircraft with them. However they lacked radar, were not very maneuverable under water and due to their weak hull they could not dive deep. At the end of the war, the submarines were used to transport supplies to island garrisons.
Meanwhile the US used their submarines to attack merchant shipping, destroying more Japanese shipping than all other weapons combined. While the British and Japanese also fielded attack submarines, they were used in fleet actions where they were almost useless due to their low speeds.
Diesel-fuelled submarines needed air to run their diesel engines, thus they carried very large batteries for submerged travel. These batteries limited the speed and range of the submarines while submerged. The schnorkel was used to allow German submarines to run just under the surface, attempting to avoid detection visually and by radar. The German navy experimented with engines that would carry peroxide to allow diesel fuel to be used while submerged, but technical difficulties made this infeasible. On the other side, the Allies experimented with a variety of detection systems, including chemical sensors to "smell" the exhaust of submarines.
In the 1950s, nuclear power partially replaced diesel-eletric propulsion in those nations with access to nuclear technology. Equipment was also developed to extract oxygen from sea water. These two innovations gave submarines so equipped the ability to remain submerged for weeks or months, and enabled previously impossible voyages such as USS Nautilus's crossing of the North pole beneath the Arctic ice cap in 1958. Most of the naval submarines built since that time in the United States and the Soviet Union/Russia have been powered by nuclear fission reactors. Use of nuclear power instead of fossil fuel enables submarines to travel around the world submerged and essentially hidden for months at a time. The most limiting factors in the length of time staying submerged now are food supply and willingness of the crew to remain in the space-limited submarine.
While the greater endurance and performance from nuclear reactors mean that nuclear submarines are the norm, conventional diesel-electric submarines have continued to be produced by both nuclear and non-nuclear powers. Conventional submarines are cheaper to build. When running on batteries they are often quieter than nuclear submarines, giving a tactical advantage.
During the Cold War, the United States of America and the Soviet Union maintained large submarine fleets that engaged in cat-and-mouse games; Russia continues this tradition today. The Soviet Union suffered the loss of at least four submarines during this period: K-129 was lost in 1968, K-8 in 1970, K-219 in 1986, and Komsomolets in 1989 (which held a depth record among the military submarines—1000 m). Many other Soviet subs, such as K-19 were badly damaged by fire or radiation leaks. The United States lost two nuclear submarines during this time: USS Thresher (SSN-593) and USS Scorpion (SSN-589).
The United Kingdom employed nuclear-powered submarines against Argentina in 1982 during the two nations' dispute over the Falkland Islands. The sinking of the antiquated cruiser ARA General Belgrano by HMS Conqueror was the first sinking by a nuclear-powered submarine in wartime.
In 2000, a Russian Oscar II-class submarine (which is the world's largest cruise-missile submarine), the Kursk, sank in the Barents Sea when a leak of hydrogen peroxide in the forward torpedo room caused a spontaneous detonation of the warhead. In 2001, the American submarine USS Greeneville accidentally struck and sank a Japanese ship, Ehime-Maru, killing nine Japanese crewmen. In August 2003, the Russian nuclear November class submarine K-159 sank in the Barents Sea. The submarine was decommissioned, and it had only ten crew on board.
Until the advent of nuclear marine propulsion, most 20th century submarines used batteries for running underwater and gasoline (petrol) or diesel engines on the surface and to recharge the batteries. Early boats used gasoline but this quickly gave way to diesel because of the greatly reduced flammability of diesel. The diesel-electric submarine became the standard means of propulsion. Initially the diesel or gasoline engine and the electic motor were on the same shaft which also drove a propellor 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 if 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 propellor. 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 submarines designs, particularly those of the US 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 allowed much more flexibility, for example the submarine could travel slowly on the surface whilst the engines were running at full power to recharge the batteries as quickly as possible.
There were other power sources tried—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. This was selected to give them the necessary surface speed to keep up with the British battle fleet.
Steam power was resurrected in the 1950s with the advent of the nuclear-powered steam turbine driving a generator which is now used in all large submarines. These vessels nevertheless always have a small battery and diesel engine/generator installation for emergency use should the reactor have to be shut down.
At the end of the Second World War the Germans and later the British experimented with Hydrogen Peroxide/Kerosine 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, but several navies, notably Sweden now use Air-Independent Propulsion boats which substitute liquid oxygen for hydrogen peroxide.
Most small modern commercial submarines which are not expected to operate independently just use batteries which can be recharged by a mother-ship following every dive.
Numerous films have been inspired by the danger, drama and claustrophobia of being on a submarine, and the suspense of the cat-and-mouse game of submarine or anti-submarine warfare. Titles include:
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