A submarine is a self-propelled vessel capable of operating underwater. The submarines that were used in the two world wars could remain underwater for only a few hours at a time. They functioned at the surface for long periods and had to be so designed, with sharply pointed bows and long, slender hulls. In contrast, vessels designed primarily for underwater operation, such as nuclear submarines (the first true submarines), instead have a relatively broad tear shape or fish shape with a blunt, rounded bow and a drawn-out, tapering stern. In addition, whereas surface hulls are designed with the greatest breadth above the waterline for surface stability, underwater hulls have generally circular cross sections that increase hull strength and reduce surface area and friction drag.
A more general term also used for devices designed to operate underwater is "submersible." Such devices range from diving bells and BATHYSPHERES to the balloonlike BATHYSCAPHES and the many small research craft available to explore the ocean depths (see OCEANOGRAPHY).
BASIC SUBMARINE STRUCTURE
A submarine is fundamentally an air space contained by a hull that is designed to withstand deep ocean pressures and to move easily underwater. The hull is a double steel shell. The inner, or pressure, hull contains all the machinery for propelling and guiding the vessel, plus living quarters for the crew. The outer hull holds the ballast tanks. When the vessel submerges, these tanks are opened and flooded with seawater. For surfacing, the seawater is forced out of the ballast tanks and replaced by compressed air.
Flooding the ballast tanks is only one step in the process of submerging. The submarine is also propelled downward by rear-mounted propellers that force the craft forward, and by diving planes, which are movable horizontal rudders that direct the angle of the dive. When the desired depth is reached, the water level in the vessel's trim tanks is adjusted to keep the craft stable.
Nonnuclear submarines are propelled on the surface by diesel engines; when submerged, propulsion is provided by electric batteries and motors. The batteries must be recharged on the surface by the diesels after a short running time. Nuclear submarines are powered by a shielded nuclear reactor that generates steam to turn the propulsion turbines and also supplies electricity for subsidiary systems such as lighting, the vent controls of the ballast tanks, the operation of the torpedo tubes, the periscope, and the maintenance of the life-support systems--the air and water supply that is manufactured on board.
Nuclear power generation is self-contained: because it does not involve combustion, it does not draw oxygen from the vessel's air supply. In addition a nuclear reactor can power a submarine for many thousands of kilometers without refueling. Nuclear submarines therefore have a virtually unlimited range.
Until after World War II, submerged submarines were navigated with a simple magnetic compass, supplemented by periscopic sextant shots and observation of the shoreline. Most periscopes could not be used at depths greater than 9 m (30 ft). Improvements in gyroscopic navigational aids ultimately led to the development of modern inertial navigation systems capable of providing accurate guidance without the need for frequent external "fixes" (see GUIDANCE AND CONTROL SYSTEMS).
The Conning Tower
The fin-shaped superstructure mounted on top of the submarine serves as a bridge when the vessel is on the surface. It holds a number of instruments: the periscopes, the various radio and radar antennas, and the snorkel, a system of air intake and exhaust pipes. On nuclear submarines the conning tower is known as the "sail" and carries a set of diving planes.
The first craft known to have maneuvered underwater was constructed by Cornelis DREBBEL, court engineer to James I of England, and was demonstrated on the Thames in 1620. Propelled by oars sealed at the locks by leather gaskets, it apparently submerged by admitting water into the hull and surfaced by pumping it out again.
Although the idea of the submarine continued to intrigue inventors, the lack of a power source to propel the vessel was a major obstacle to its development. The wooden TURTLE, designed by David BUSHNELL, an American, was driven by hand- and foot-cranked propellers. Its armament was an explosive charge that, in theory, could be fastened to an enemy ship's hull by a detachable auger. The Turtle's one foray (1776), against a British ship lying off New York harbor, was frustrated in part by the difficulty of maneuvering the vessel underwater.
In 1801, Robert FULTON demonstrated his three-man metal submarine, the NAUTILUS, for the French navy. Like the Turtle, the Nautilus was driven by a hand-cranked propeller, but for depth control it had movable horizontal surfaces--the diving planes now used on all modern submarines. Its warhead was a towed contact mine, designed to explode when it was dragged against the enemy target. The military potential of the Nautilus was never realized in its time, but it presaged the first successful submarine attack, over 60 years later, by the Confederate vessel Hunley.
Submarines in the U.S. Civil War
In response to the Northern blockade of shipping during the Civil War, the Southern navy developed a group of semisubmersibles known as "Davids"--small craft intended to battle the Union's Goliath fleet. Although not true submersibles--their smokestacks and air intakes were always above water--they were the first vessels to use submergence with tactical success.
Another Confederate development was the Hunley, a true submersible. Although it used the old hand-cranked propeller system and was slower than the "Davids," it could submerge completely. Fitted with a spar torpedo--a 6-m (20-ft) pole tipped with an explosive charge--the Hunley went down on the night of Feb. 17, 1864, sinking a Federal corvette, the U.S.S. Housatonic, off Charleston but destroying itself in the process.
At the same time, European submarine technology was also accelerating. In 1863 the French inventor Charles Brun used compressed air to propel his vessel, the Plongeur, and to expel water from its ballast tanks, a method that is still used. The French navy built several all-electric submarines in the 1880s and '90s. These demonstrated the potential of electric power underwater but were severely limited by the need to recharge the batteries in port. They had no engines other than their battery-powered electric motors. Robert Whitehead's self-propelled TORPEDO gave the submarine a genuine offensive capability; the Swedish inventor Torsten Nordenfelt (1842-1920) developed internal torpedo tubes for submarines in the 1880s.
The Irish-American John P. HOLLAND (1840-1914) had experimented with submarine designs for a quarter century when he sold (1900) the U.S. Navy its first submarine. The U.S.S. Holland used an electric motor for propulsion underwater and a gasoline engine for surface propulsion and for recharging the batteries. The submarines of the two world wars differed in basic design from the Holland only in the substitution of diesels for the gasoline engine. Like most later submarines, the Holland submerged by flooding its ballast tanks, used trim tanks and diving planes to control pitch when submerged and fired torpedoes and blew the ballast tanks empty with compressed air.
World War I
From the early years of the 20th century, fleets of submarines were built by every major European power. The German vessels were the most efficient; by 1911, German designers had abandoned both steam and gasoline--which was volatile, and therefore hazardous within the confines of a submarine--and had equipped all their vessels with diesel engines. Also, German periscopes were the best in the world.
World War I provided the first opportunity to use submarines as attack vessels on a large scale. With its fleet of U-boats (Unterseebooten), Germany came close to severing Britain's overseas lifelines. Britain countered with efforts to confine the German submarines to their ports, using air and surface patrols and laying MINE belts.
DEPTH CHARGES and hydrophones--underwater listening devices--were developed and used extensively; the British successfully employed killer submarines as well--small antisubmarine vessels that could maintain underwater speeds of up to 15 knots for as long as 2 hours. Finally, merchant sailings were concentrated into large, well-escorted convoys, a tactic for which the Germans had not found an answer by the war's end.
World War II
As in World War I, Germany began World War II with a small but seasoned submarine force and immediately applied it to isolate Britain from overseas resources. Britain again replied with heavily escorted convoys, and the Germans responded by sending U-boats out in large "wolf packs" that used radio communications to search and attack in concert.
Tactical complexities multiplied: hydrophones were supplemented by underwater sound-ranging systems (SONAR) and the use of RADAR and radar warning devices became widespread. The Germans used long-range search aircraft to coordinate the wolf packs; the British and Americans replied with antisubmarine aircraft carriers and fleets of hunter-killer submarines that were guided to the German vessels by sensitive high-frequency direction-finding radios installed aboard surface vessels.
American submarines in the Pacific and British submarines in the Mediterranean enjoyed the success denied the Germans in the Atlantic. Submarine destruction of Axis supplies played a major role in the Allied victory in North Africa. American submarines effectively halted Japanese maritime commerce by mid-1944. Britain and Italy both had isolated but spectacular successes with miniature one- and two-man submarines in port attacks on enemy ships.
THE NUCLEAR SUBMARINE
The first nuclear submarine, the U.S.S. NAUTILUS, launched in 1954, resembled conventional submarines in many respects, but its great range both above and below the surface made it a revolutionary and formidable weapon. The Nautilus sailed almost 170,000 km (91,324 naut mi) before refueling; 146,000 km (78,885 naut mi) were spent submerged. On August 3, 1958, it sailed under the Arctic ice and the North Pole.
Following the Nautilus and a group of submarines of the same design, the U.S. Navy developed the Skipjack class of nuclear submarine, which had a teardrop-shaped hull design and was capable of reaching underwater speeds of more than 30 knots. Succeeding types of nuclear submarines, the Thresher and Sturgeon classes, have been designed to be high-speed detection and attack vessels. The U.S.S. Triton, launched in 1959, is among the largest and is propelled by two nuclear reactors. In 1960 the Triton circumnavigated the globe underwater, traveling 78,858 km (41,500 naut mi) in 84 days.
Whereas the nuclear attack submarine represents the most advanced use of hydrodynamic technology, the nuclear BALLISTIC MISSILE submarine is perhaps the ultimate development of the submarine's military potential, having the ability to launch as many as several dozen intercontinental ballistic missiles while submerged. Following the first underwater launch of a POLARIS missile from the U.S.S. George Washington in 1960, such submarines have entered the U.S. and Soviet navies in increasing numbers and are also possessed by Great Britain and France. U.S. nuclear submarine classes include those carrying the POSEIDON missile and a growing new fleet of TRIDENT submarines, which were first launched in the early 1980s.