Introduction to Submarine
Submarine, a vessel designed to operate below the surface of the water. Submarines were of major importance in both World Wars and today rank with aircraft carriers as the most important ships in the world's navies. The development of nuclear-powered submarines, which have unlimited range and can cruise at high speeds underwater, has revolutionized naval strategy by placing the main emphasis on undersea, rather than surface, warfare. Non-naval submarines are important tools in ocean research and exploration of the ocean floor.
Research submarines are generally called submersibles and are not discussed in this article. (Technically, a submersible is any underwater vessel; a submarine is a submersible that operates without being tended on the surface; and a true submarine is a submarine that is more efficient underwater than on the surface and does not require periodic contacts with the atmosphere to obtain oxygen for the crew.)
Russia has the largest submarine fleet in the world, and about half of it is nuclear powered. The United States has fewer submarines, and all of them are nuclear powered. The U.S. Navy is a leader in the development of noise-suppression technology and of weapons for antisubmarine warfare (ASW). Many other countries include submarines in their naval fleets. These countries include not only major Western powers like Great Britain, France, and Germany, but also less-developed nations like Singapore, Oman, Indonesia, and Saudi Arabia.
Nuclear submarines are of two basic types—attack submarines and ballistic-missile submarines. Conventional submarines are also of two basic types—the long-range cruiser submarines and the small, short-range coastal submarines.
The U.S. Navy names its attack submarines after sea creatures, cities, states, and notable persons. Its ballistic missile submarines are named after states.
Uses of Submarines
Submarines of all types are used to attack and sink enemy surface vessels and submarines. However, the attack type is the most effective. Specialized attack types called hunter-killer submarines are designed to destroy other submarines. Guided missiles make submarines effective against shore targets and more dangerous than ever before to shipping and naval vessels. Some submarines are designed to launch ballistic missiles with nuclear warheads; no point on earth is beyond the range of these missiles.
A number of important secondary uses for submarines developed during World War II. Submarines carried ammunition and supplies to ports that were surrounded by the enemy. The U.S. Navy submarine Trout brought out gold, silver, and valuable securities from the Philippines. Soldiers were sometimes sent ashore from submarines for surprise raids, and submarines were used extensively to rescue downed aviators.
In sea warfare, a submarine attempts to avoid detection while getting within effective torpedo range of enemy ships. The main purpose of the U.S. Navy's ballistic-missile submarines is to make it unprofitable for an enemy to launch a surprise nuclear attack. By constantly moving about while remaining within range of their targets, such submarines make it virtually impossible for an aggressor to destroy all of the United States' means of launching a nuclear counterattack.
Design
A submarine is built with ballast tanks (“trim tanks”) to control its depth and its horizontal orientation. The ballast tanks have large openings, called flood-ports, at the bottom and vent valves at the top. When the submarine is on the surface the ballast tanks are partly filled with air to provide positive buoyancy. The submarine is submerged by opening the vent valves, allowing air to escape and water to fill the tanks through the flood-ports and thus provide negative buoyancy.
A submarine is also controlled by rudders and by diving planes that extend from the sides. The diving planes are like small airplane wings that can be tilted up or down to make the submarine go up or down through the water.
Because of the depth at which submarines cruise—usually about 1,000 feet (300 m) below the surface—they require reinforced hulls, called pressure hulls, to withstand the water pressure. Submarines may be built with single hulls or double hulls. The United States, Great Britain, France, and Germany generally build single-hull submarines; Russia prefers double-hull submarines. (In double-hull submarines, the inner hull forms the pressure hull. The space between the inner and outer hulls is divided into compartments for fuel and ballast.)
Most submarines have streamlined hulls for maximum efficiency while submerged. The most common streamlined design is the teardrop shape pioneered by the U.S. Navy for its nuclear-powered submarines and gradually adopted for both nuclear and conventional submarines by all navies. The teardrop shape sacrifices speed on the surface for underwater efficiency. Some navies of minor powers are equipped with old conventional submarines that have prominent bows and other features that make them more efficient on the surface than underwater.
Conventional submarines are about 310 feet (94 m) long with a beam (width) of about 27 feet (8 m). Nuclear submarines range in length from 250 feet (76 m) to about 560 feet (171 m); their hulls have beams ranging from 25 to 40 feet (8 to 12 m).
Old conventional submarines have a surface speed of about 14 to 18 knots and a submerged speed of about 10 to 12 knots. Modern conventional submarines have surface speeds of 10 to 12 knots and submerged speeds of about 16 to 20 knots. Nuclear submarines have surface speeds of about 15 to 20 knots and submerged speeds of about 30 to 45 knots.
EnginesA conventional submarine has a diesel-electric propulsion system. In such a system, a diesel engine is connected to an electrical generator that powers an electric motor, which drives the propeller shaft. At the same time the generator charges a bank of storage batteries. Because diesel engines require air, conventional submarines usually operate on the surface or approximately 50 feet (15 m) below the surface using a snorkel, an air tube that extends above the water. The disadvantage of a snorkel is that it creates a telltale wake.
To run submerged at greater depths diesel-electric submarines derive power from storage batteries. On battery power they can stay submerged up to a week while running at low speed; at high speed most can operate for only a few hours.
Power for nuclear submarines comes from a nuclear reactor. In the reactor a controlled chain reaction of uranium heats water under high pressure. This pressurized water is circulated through heat exchangers (boilers) which generate non-radioactive steam at moderate temperature and pressure. The steam drives turbines that, in turn, drive generators for supplying ship's electricity. The ship's propellers are driven by the turbines through a mechanical linkage or by electric motors powered by the turbine's generators. Heavy shielding around the reactor and boiler protects the crew and surrounding environment from radiation.
A single charge of uranium fuel can produce enough power to drive the submarine for many months. The nuclear power plant does not require oxygen and can therefore be used underwater as well as on the surface. Also, the engine is much more powerful than the electric motors of conventional submarines.
Special EquipmentWhen the submarine is near the surface, periscopes are used to see above the surface. Most submarines have two periscopes, a large-aperture one for search and scanning and a small-aperture one for use in attacks. The periscopes may incorporate television cameras and infrared sensors to enhance vision; videotape recorders may be used to provide a record of sightings and attacks.
During long periods underwater the air inside a nuclear submarine is purified by equipment that removes carbon dioxide and replaces oxygen breathed in by the crew members. The oxygen is generated from sea water by an electrical process. (Conventional submarines, which must surface periodically to charge their batteries, do not have this equipment.)
The size of a submarine crew ranges from 18 to 22 for a small coastal submarine, from 25 to 80 for a conventional submarine, and from 90 to 150 for a nuclear submarine. The quarters on a nuclear submarine are roomier and more comfortable than those on a conventional submarine because crew morale becomes a concern when a submarine spends weeks submerged. The U.S. Navy has two crews for each nuclear submarine, one replacing the other at the end of a cruise.
For underwater detection of ships and for some navigational purposes, submarines use two kinds of sonar. Active sonar sends out sound to bounce off a target and then receives its echo. It is used to locate underwater hazards and at times to determine the range and direction of target ships. Because active sonar transmits a revealing signal, however, submarines generally avoid using it to locate enemy vessels. For this purpose they rely mainly on passive sonar, which uses an array of hydrophones (listening devices) embedded in the hull to listen to various noises from the target ship, particularly its propeller.
Inertial guidance (called Ships Inertial Navigation System, or SINS, in the U.S. Navy) is a system of navigation that permits a submarine to fix its position without coming to the surface. Inertial guidance was originally developed for missiles and is explained in the article missiles and rockets, section “Military Missiles,” subtitle Guidance Systems: Missiles Guided in Flight (Preset Guidance).
ELF (extremely low frequency) radio waves are used for long-distance communication with submerged submarines. Unlike the radio waves used for conventional radio communications, ELF waves can penetrate deep into seawater. However, ELF radio waves are inefficient for sending long messages and they require that the submarine use a very long trailing-wire antenna.
WeaponsUntil after World War II, most submarines had deck guns; today only older submarines carry these weapons. All submarines carry torpedoes, which are used against other vessels. On most new submarines they are fired from tubes along the sides near the bow, but on older submarines they are fired from forward tubes (tubes in the bow itself) and aft (rear) tubes.
Submarines may also carry guided, cruise, and ballistic missiles. Guided missiles have a range of some 70 miles (110 km), and cruise missiles have a range of some 1,550 miles (2,500 km). Both are launched underwater, either from torpedo tubes or from vertical tubes in the bow, and then fly through the air toward surface targets.
Ballistic-missile submarines can launch their weapons while submerged and are capable of hitting land targets up to 4,600 miles (7,400 km) away. These missiles usually have multiple warheads, each of which can be directed at a different target. These submarines have few tactical weapons. The U.S. Navy's fleet ballistic-missile submarine, with only 4 torpedo tubes, has as its principal armament 16 intermediate-range Poseidon or Trident missiles. A few are armed with 24 Trident missiles.
Antisubmarine Warfare
Antisubmarine warfare (ASW) is the branch of naval warfare devoted to denying the enemy effective use of his submarines. It includes not only the seeking out and destroying of enemy submarines, but also passive defensive measures (such as sailing in a zigzag course) and the destruction of the enemy's submarine bases. ASW was of major importance in both World Wars and, with the development of nuclear-powered submarines carrying nuclear-armed missiles, has become even more important since.
Many types of naval vessels and aircraft carry instruments that can detect and weapons that can sink submarines. The most effective weapon against a submarine, however, is another submarine. Attack, or hunter-killer, submarines, developed after World War II, are designed for the specific purpose of finding and destroying enemy submarines. They carry a variety of detection devices and antisubmarine weapons, and can operate either independently or in close coordination with surface ships and aircraft.
In both World Wars I and II, the convoy system, in which Allied merchant ships traveled in large groups protected by escort vessels (mainly destroyers and cruisers), was the most effective measure used to prevent German submarines from dealing a death blow to Allied shipping. In World War II, air cover (airplanes or blimps) was also used to protect convoys. Aircraft from escort carriers (CVE's) were especially effective.
Detection of SubmarinesSonar was widely used in World War II and is the most important instrument for detecting enemy submarines. An important consideration in submarine design is the reduction of selfnoise (the noise made by the submarine itself) to the lowest possible level—both as a defense against enemy vessels' passive sonar and to increase the effectiveness of the submarine's own passive sonar. Many submarines and ASW surface ships tow sonar arrays at some distance behind them to minimize the interference caused by self-noise.
Sonar equipment is carried by ASW helicopters and airplanes as well as by submarines and naval surface vessels. Helicopters and airplanes drop expendable sonar-equipped floats called sonobuoys into the water where the presence of an enemy submarine is suspected. Each sonobuoy has a radio transmitter to send sonar data to monitoring aircraft or surface ships in the vicinity. Helicopters also use dunking sonar, or dipping sonar, a sonar array that is lowered into the water while the helicopter hovers.
Thermoclines—layers of water in which the temperature of the water changes rapidly with increasing depth—tend to reflect sound waves. Sonar equipment called variable-depth sonar is designed to be lowered by cable through a thermocline to detect any submarines positioned below it.
Networks of seabed sonar devices have been installed in navigational channels through which submarines must usually pass. The United States maintains such a network, called SOSUS (sound surveillance system), at several strategic locations.
Radar, usually located on retractable masts, can detect surfaced submarines at distances as far as the horizon but cannot detect submerged submarines because the electromagnetic waves used in radar will not penetrate water effectively.
The radio direction-finder “net,” consisting of a widely scattered group of ships equipped to pick up enemy radio transmissions, was used in World War II to locate enemy submarines. The positions of the submarines were obtained by using cross bearings (compass bearings taken simultaneously from two or more ships). Electronic-countermeasures (ECM) equipment installed on aircraft, surface ships, and submarines is used to locate enemy submarines while on the surface by picking up their electronic transmissions.
The magnetic-anomaly detector (MAD) is a device that detects distortions (anomalies) in the earth's magnetic field that are caused by submarines. It works on the principle that a piece of magnetic material (for example, a steel submarine), when placed in a magnetic field, will distort the lines of force associated with the field. The magnetic-anomaly detector is carried by an aircraft, and its chief component is an instrument called a magnetometer. The range of the MAD is so short that a MAD-equipped aircraft has to be almost directly above a submarine before the device will indicate the submarine's presence.
Some artificial satellites carry equipment that has been developed for detecting submarines. This equipment includes infrared (thermal) detectors that are sensitive enough to detect the low levels of heat in a submarine's wake.
Destruction of SubmarinesAt the beginning of World War I, the first war in which submarines were used extensively, the only measures available against enemy submarines were gunfire, ramming, minefields, and antisubmarine nets. Minefields and nets were used to prevent enemy submarines from passing through certain areas, such as entrances to harbors, and are still available for this purpose..
Torpedoes orginally were intended to be used only against surface ships but subsequently were developed into effective antisubmarine weapons. They can be launched from airplanes, surface ships, or submarines. A subroc is a rocket-propelled torpedo.
Homing torpedoes (also called acoustic torpedoes) were developed during World War II. A passive homing torpedo is designed to detect the sound of a submarine's propellers or engines and home in on it; an active homing torpedo uses a tiny echo-sounding device to find its target. A wire-guided torpedo is controlled by signals transmitted through a wire connecting it to the launching ship. The variable-speed torpedo moves slowly as it approaches a target ship. Once it is at close range, the torpedo accelerates greatly, to make evasive maneuvers by the target ship very difficult.
Depth charges were developed during World War I. They are carried by surface ships and are either fired from deck guns or dropped over the side or stern of the attacking ship. The depth at which they explode can be preset. Depth bombs are similar to depth charges but are dropped from aircraft.
The hedgehog, a rocket-propelled antisubmarine weapon, was developed during World War II. Twenty-four hedgehog charges are fired simultaneously from a 24-tube gun and land ahead of the attacking ship in a circular pattern about 200 feet (60 m) in diameter. A hedgehog charge—unlike a depth charge—explodes only if it hits the target, and therefore the sonar search for the enemy submarine can continue without being adversely affected by explosions in the water. Its short range, about 285 feet (87 m), is ill-suited for modern warfare.
History
Early TypesThe first successful submarine was invented in 1620 by Cornelis Drebbel, a Dutch physician, who conducted several tests in the Thames River. The vessel, propelled by oars, consisted of a wooden frame covered with greased leather.
The use of a submarine as an offensive weapon was first tried in the American Revolutionary War. In 1775 David Bushnell, a physician in the American colonies, devised a wooden, egg-shaped, one-man submarine, the Turtle, for use against the British fleet in New York Harbor. The following year Sergeant Ezra Lee maneuvered the Turtle into the harbor and under a British man-of-war. After failing in an attempt to attach a gunpowder charge to the ship's hull, he set the charge off a short distance away. The explosion so frightened the British that they moved their fleet.
In 1801 Robert Fulton built for the French navy a wooden submarine, the Nautilus, for use against the British. It had such features as a conning tower and ballast tanks. Four men inside manually operated a propeller mechanism. Fulton failed in several attempts to destroy any British ships, and the French withdrew support.
During the American Civil War, the Confederates built partly submersible vessels called “Davids,” in which the entrance hatch and funnel remained above water. No Union ships were sunk by them, however. The Confederates also built a completely submersible craft, the Hunley, named after its inventor, H. L. Hunley. It was built of sheet iron and was propelled manually. In trial runs the vessel sank four times with full crews of eight men each. In 1864, the Hunley, sailing partly submerged, sank the USS Housatonic with a spar-torpedo, an explosive on the end of a pole. This was the first time a warship had been destroyed by a submarine; the Hunley, however, also went down.
In both Europe and the United States, many inventors in the late 1800's worked on developing a submarine that could operate as a practical and effective warship. John P. Holland, an Irish-American, is generally credited with being the first to invent such a craft. His first model was built in 1877. One of his vessels, the Holland, launched in 1898 and accepted by the United States government in 1900, was the first U.S. Navy submarine.
Holland introduced steel construction for the hull, the use of electric storage batteries for powering the vessel under water, and the use of the internal combustion engine when on the surface. Simon Lake, another United States inventor, devised a submarine that could dive on an even keel instead of nose first like Holland's vessel. Using these American developments, other nations built their submarine fleets. An innovation of the Germans was the diesel engine, first used in 1909.
The Two World WarsGermany had built fewer submarines than any major power before World War I. But after the war broke out in 1914, Germany saw the possibility of using U-boats (Unterseeboote, “undersea boats”) to destroy the commerce of Great Britain and force the country out of the war by economic strangulation. Although limited by operational radius to European waters, the submarine proved extraordinarily effective, as thousands of Allied merchant vessels were sunk. Many warships were sent to the bottom as well.
The U-boats would have been valueless, however, had Germany abided by international law and provided for prior visit and search of the target ship and for safety of its passengers. The United States protested unrestricted use of the U-boat, especially when American lives were lost, and eventually Germany's U-boat campaign brought the United States into the war.
British measures to combat the U-boat menace, such as laying mine fields and patrolling shipping lanes, were largely ineffective. It was not until the convoy system was introduced in 1917 that massive destruction of merchant shipping was ended. Near the end of the war, the British perfected the hydrophone and used it in antisubmarine warfare. After the war, further improvements on the device resulted in the development of sonar.
In the early part of World War II, the inability of the Allies to fully maintain the convoy system and air cover, as well as a lack of sonar and radar equipment, resulted in great losses in seaborne shipping to German U-boats. Unlike World War I submarines, World War II U-boats, refueled in the mid-Atlantic Ocean by U-boat tankers, could roam the entire ocean. German policy was to concentrate operations where there were few convoys and where there was light antisubmarine activity. Against convoys, night surface attacks by “wolf packs” (teams of submarines) met some success.
By the end of 1944, however, the Allies had overcome the submarine peril by extending the convoy system and by greater use of detection equipment and aircraft carrier and land-based air cover. In 1944 the Germans adopted the snorkel, which enabled their submarines to recharge their batteries at periscope depth, thereby decreasing chances of being detected by radar. The Germans also developed submarines with greatly improved underwater capabilities. It was too late in the war, however, for these developments to benefit the Germans to any great extent.
United States submarines were extremely effective due in part to the excellent training of their crews and in part to the poor antisubmarine warfare performance of the Japanese navy. Virtually all of Japan's seaborne commerce was destroyed, which contributed greatly to that nation's defeat. Japan experimented with one-man midget submarines, and some were used in the attack on Pearl Harbor. However, throughout the war the Japanese used their submarines ineffectively and employed them little against merchant shipping.
Nuclear SubmarinesThe nuclear submarine was developed by a group headed by Hyman G. Rickover of the U.S. Navy. Work began in 1947. The world's first nuclear-powered vessel, the submarine Nautilus, was launched in 1954, followed by the Seawolf in 1955. The underwater cruising ability of nuclear submarines was demonstrated by the voyage of the Nautilus to the North Pole in 1958 and the around-the-world submerged voyage of the Triton in 1960.
The first submarine equipped with ballistic missiles, the USS George Washington, went to sea duty in 1960. The United States in the 1990's had more than 30 such submarines. China, Great Britain, France, and Russia have built nuclear-powered attack submarines as well as ballistic-missile-carrying types.