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A submarine is a ship that can travel underwater. Most submarines, particularly large ones, are warships belonging to some country's Navy, but there are some civil submarines[1][2][3][4]. A naval submarine warship routinely moves, detects targets, and attacks them while under the surface water. Submarines are the original "stealth" weapons of war; their greatest strength is the challenge, to anti-submarine warfare forces, to find the submarine and localize it sufficiently to aim weapons at it. Of course, once a submarine attacks, any surviving enemies now know it is in the general area; submariners call this a "flaming datum" (referring to the target), and "clear datum" as quickly as consistent with not being detected.

There are two kinds of vessels: submarines and targets — a motto of submariners worldwide

"We hide with pride", and the "silent service", are informal and formal mottoes of undersea warfare. Traditionally, submarines are called "boats", even though some missile-launching submarines displace as much as a World War I battleship.

The submerged time of a submarine first depends on its propulsion system. A nuclear-powered submarine is limited by the endurance of its crew, and often by the amount of food it can store. Air-independent propulsion submarines are limited by the amount of fuel and oxidizer, or monopropellant, they carry to run their engines and generators. Diesel-electric submarines are limited by the capacity of their batteries to hold an adequate electrical charge for operations.

To some extent, modern diesel-electric submarines, and the versions of the First and Second World Wars, are more submersibles than submarines. They have to do a significant amount of cruising on the surface, while charging their batteries. While long-endurance nuclear submarines can be an optimal shape to travel underwater, which is poor for surface operations, battery-operated boats. have to compromise their design to let them function on and below the surface.

Submarine design

Just as surface warships classically have to balance armament, protection and speed, submarines need to balance even more factors:

  • Speed
  • Endurance
  • Operational depth
  • Quietness
  • Habitability
  • Armament

Once nuclear propulsion was introduced, endurance became much less of a factor: nuclear submarine patrol duration is principally limited by the amount of food that can be carried. Modern non-nuclear submarines with air-independent propulsion did not have different surface and underwater propulsion systems, as did the diesel-electric boats.

Submarines can travel on the surface of the water, snorkel just below the surface [5] or at periscope depth,[6] or travel deeper underwater. However at great depths, the hydrostatic pressure of the water becomes too high for submarines to withstand for all but a few specialized submarines. Submarine propulsion is by a rotating propeller located at the aft (rear) of the ship. The propeller is placed outside the hull at the end of a shaft driven from an engine room inside the submarine. In many submarines, normally movement through the water and associated lift keeps the submarine around desired depth, but there are ballast tanks,[7] normally filled with water, which can be filled with air from a compressed air supply to make the submarine bouyant.

At certain points along the top of the hull, there are watertight hatches for entry and exit. Such hatches can also be included in bulkheads (walls between rooms or compartments) inside the ship. There are openings in the hull for seawater entry or exit as needed; for example, filling ballast and trim tanks.

Pre-technological submersibles

Among the first operations carried out by a pre-technological submersible was by the Turtle during the American Revolution. It was a roughly barrel-shaped one-man vehicle, powered by turning a crank. The lone operator, Sergeant Ezra Lee, was able to get underneath his British warship target, and stay undetected, but his weapon was not adequate. It was a fused container of gunpowder, which was to be attached, by a screw, to the hull. Unfortunately for the attacker, the hull had freshly been covered with sheets of copper, and those sheets, intended to deter barnacles and other parasites, were too strong to be penetrated by the screw drill. The Turtle and her operator survived.

While the crew was not as lucky as that of the Turtle, the Confederate CSS H.L. Hunley did attack and sink the USS Housatonic during the American Civil War. Again, the submarine was muscle powered. Her weapon was a "spar torpedo", or barrel of gunpowder, with a trigger on a long cord, at the end of a wooden spar projecting from the bow. It was able to approach the Housatonic, successfully detonate its weapon and destroy the target, but the Hunley sank shortly afterward, from unknown causes. The submarine may have lasted for an hour or longer after hitting its target, but was found recently on the bottom, with the crew at their stations, apparently not trying to escape. While exact cause of death cannot be determined from the skeletal remains, the lack of attempt to escape suggests asphyxiation or exhaustion as a cause.

Early technological submarines

The first Plunger, was a steam-powered submarine built in 1895.
The USS Plunger, the US Navy's first submarine.

In 1895 the United States Navy contracted with John P. Holland for the construction of a steam-powered submarine, named the Plunger.[8] This design as not accepted, so Holland's company supplied the US Navy with an improved design, the US Navy's first submarine, which was commissioned the USS Plunger, in 1902.[9]

First World War

By the First World War, the first technological submarines had the basic components allowing true underwater operations:

  • Batteries and electric motors for underwater propulsion, charged while running an air-breathing engine on the surface
  • A free-running torpedo, derived from the Whitehead design of 1866, which let the submarine make an underwater attack from a safer distance. These torpedoes ran a straight line, and had to be fired on a collision course with the target
  • Periscopes to allow visual observation of targets and threats while submerged.
  • Acoustic sensors (passive microphones) to detect the general target, although visual observation was needed for aiming.

Submarines had a significant if supportive role in the First World War, sinking a number of warships and major transports.

Second World War

In the Second World War, however, submarines (SS) had a vital role. German submarines, called U-boats nearly cutting off supplies to Britain during the Battle of the Atlantic. They were narrowly defeated by intensive Allied research into antisubmarine warfare, coupled with excessive radio reporting to and from Admiral Karl Doenitz, commanding the German submarine arm. The Germans never realized how deeply the Allies had penetrated their communications, both direction-finding on transmissions and reading encrypted messages. Eventually, roughly 75 percent of U-boat sailors died in action. Both of Doenitz's sons died on missions.

U.S. submarines also took a massive role in cutting off supplies to another island nation, Japan. Japan, however, was not as effective as the Western Allies in antisubmarine warfare. While their submarines had the best torpedoes of the war, they had ineffective doctrine: it was a facet of the warrior culture that warships were considered more important than transports, and many submarines were diverted to supply isolated island garrisons.

When Admiral Chester Nimitz took over the Pacific command at Pearl Harbor, his change of command ceremony was on the deck of a submarine. The U.S. "silent service" started slowly, with defective torpedoes. Once the faults were corrected, they had a fearsome effect, both cutting off supplies to the Japanese home islands, and also having significant warship kills. They were assisted by the Japanese not treating anti-submarine warfare as a high priority.

Casualties were heavy among the submarine services of all nations. Submariners respect one another, and most would speak of their lost comrades and enemies as

On eternal patrol — U.S. saying, but universal

Modern military submarines

There have been various major technological improvements to military submarines within about the past 60 years. Modern military submarines have cigar-shaped hulls (except for protruding diving planes, rudder, propeller, and a "sail" at the center top) for more efficient movement through water since fluid friction is minimized. In the past, much of the sail was used as a conning tower for the ship. Protruding from the top of the sail, there can be a periscope, snorkeling pipes, and antennae. Snorkeling is for a diesel engine's air intake and exhaust gases outlet. There are a pair of stern diving planes near the rudder at the aft of the ship, and starboard and port sail planes on the sail and/or bow planes on the starboard and port sides of the hull.

If there is a single dominant factor in submarine design, it is minimizing acoustic noise, and thus the primary means of detecting submarines. The most recent deviation from this priority was the extremely fast and deep-diving Soviet ALFA-class submarine, now all retired. Hull penetrations for periscopes and the like have been reduced in new designs such as the Virginia-class, the latest of the U.S., because they can interfere with smooth water flow. On the Virginias, for example, the periscope is entirely external, with its image transferred into the submarine through a small, fixed and streamlined penetration for optical fibers and electrical power cables.

First technological revolution: nuclear propulsion

In 1955, USS Nautilus' (SSN-571), named in conscious imitation of Captain Nemo's vessel in Jules Verne's novel, Twenty Thousand Leagues under the Sea, sent out the historic message, "Underway on nuclear power." Nuclear-propelled submarines (SSN) meant never again having to surface to charge batteries, although there was occasional need, until the air purification systems improved, to raise a snorkel to get fresh air.

The USS Nautilus showed incredible performance for the first nuclear boat, demonstrating sustained high speed rather than the crawl of battery power, and even crossing under the North Pole. Her performance was even more striking given that her hullform was still optimized for surface cruising, rather than the hydrodynamically efficient whale-like shapes of later boats.

The Soviet Union also was active in this period, and it was expected much of the Cold War would take place in the deep. Both sides put high priorities on anti-submarine warfare (ASW). The United Kingdom has a few nuclear-powered submarines.

In 1960, the USS Triton (SSRN 586) used nuclear power to become the first ship to travel around the world underwater. This voyage took 61 days.

Second techological revolution: electronics and computing

During World War II, active acoustic sonar could localize targets much better than the simple passive listening devices of the First World War, although it was still preferred, even when making a sonar-guided approach, to make final shooting observations through the periscopes.

Guided torpedoes, both air-dropped and submarine-launched, came into use late in World War II, but with primitive guidance. With the advent of solid-state electronics and computers, torpedoes could carry their own small sonar ir trail a command wire to the launching submarine. In fact, some precise observations could be made by correlating acoustic observation from the torpedo and the submarine. Passive acoustic devices made a strong comeback when onboard computers had sufficient signal processing power to calculate accurate fixes -- accurate enough that a homing torpedo could complete the attack solution -- and not suffer from the disadvantage that active sonar acted as a beacon to the enemy.

Third technological revolution: ballistic missiles

Modern Navy submarines are of two major types, with some specialized or additional roles. The two major types are: attack submarine and fleet ballistic missile submarine, sometimes informally referred to as a "boomer". Currently in the United States Navy, all major submarines are now nuclear-powered. In the U.S. Navy, attack submarine hull numbers are prefixed with "SSN", and fleet ballistic missile submarine hull numbers are prefixed with "SSBN". In the past, conventionally-powered U.S. submarines without ballistic missiles had hull numbers prefixed with "SS", but they are all decommissioned by now. Fleet ballistic missile submarines have a special section in the hull for ballistic missiles and so are larger than attack submarines, whereas attack submarines do not have such a section for ballistic missiles, although they may carry a few guided missiles. A few U.S. ballistic missile submarines have been converted to guided missile submarines, with hull numbers now prefixed by "SSGN". The guided missiles are cruise missiles. All these types of military submarines carry torpedoes. Although there have been various classes of U.S. Navy submarines in the past, U.S. attack submarines are currently in the Los Angeles class, Seawolf class or Virginia class. All ballistic and guided missile submarines are now Ohio class.

Ballistic missile submarine

The next major development certainly let submarines share, and possibly exceed, the previous queens of the sea, aircraft carriers. Other than a few early Soviet designs, ballistic missile submarines all use nuclear propulsion, and are designated SSBN.[10] In the late fifties, ballistic missiles, which could be fired from a submerged submarine, started with a range of 1000 miles. Modern submarine-launched ballistic missiles (SLBM) have the range and accuracy of an intercontinental ballistic missile, but that can be fired from an platform, perhaps in well-protected friendly waters, rather than from a silo whose position was fixed and known to the other side.

Antisubmarine warfare took great strides, but so did submarine silencing technology. It has frequently been suggested, and never denied, that the Soviets never tracked a U.S. ballistic missile submarine in its operational areas. It has been suggested that the way to find a superquiet submarine is to listen, passively, for the part of the sea that does not have the normal background noise: the problem is the underwater equivalent of finding an astronomical black hole.

The Soviets developed not only ballistic submarines and, as did the U.S., submarines to attack other submarines, but built fearsome vessels to attack U.S. carrier battle groups with long-range wake-homing torpedoes and anti-shipping missiles. The escort of a carrier battle group usually contains at least two attack submarines, as both sides agree that a submarine is the best hunter of other submarines.






Attack submarine

The first priority of SSNs was stopping ballistic missile submarines, as well as intelligence collection and special operations. Submarines kept the mission of attacking surface vessels, and, especially with Soviet designs, with anti-shipping missiles as well as torpedoes.

Nuclear-powered and some advanced air-independent propulsion versions are faster and more maneuverable than ballistic missile submarines. Diesel-electric boats are slow but modern versions can be very quiet.


Akula vs. Akula

"Akula" means "shark" in Russian. As the Cold War warmed, the Soviets, and then the Russians, revealed their previously classified names of submarine classes. It turned out that one of the their ballistic missile classes, not the boats NATO called Akulas, were actually the Akula class. So, if a Russian and an American each speak of an Akula, they refer to totally different submarines.

The Soviet Project 949 Granit-class/NATO: OSCAR I-class cruise missile attack submarine] and Project 949A Antey-class/NATO: OSCAR II-class cruise missile attack submarine were designed to kill carriers, with much larger anti-shipping missiles, the P-700 3M-45 Granat[11]/NATO: SS-N-19 SHIPWRECK than any U.S. submarine. They are designated SSGN to reflect their massive cruise missile armament. In addition, they carry a new, long-range type of 650mm wake-homing torpedoes, again optimized against carriers.

A unique Soviet system are superfast torpedoes that use rocket propulsion inside a "bubble", such as the Shkval.

Even the OSCAR classes, however, kept a generous supply of antisubmarine and dual-purpose torpedoes, for self-defense. Other Soviet/Russian classes, however, were pure SSN attack submarines, such as the Project 971 Shchuka-B-class/NATO: Akula-class</ref> attack submarine and Project 945 Barrakuda-class/NATO: Sierra-class attack submarine.

The most important targets of attack submarines were Soviet ballistic missile submarines. A move-countermove system developed, in which the Soviet SSBN might have a SSN escort, to protect the "boomer" from U.S. submarines.


A British Churchill-class attack submarine, HMS Conqueror, sank the Argentinian cruiser, ARA General Belgrano, during the Falklands War. This has been the only sinking of a naval vessel by a nuclear submarine, although both U.K. and U.S. attack submarines have fired land attack cruise missiles at real targets. Swiftsure-class and Trafalgar-class attack submarines succeeded the Churchill class.

United States

Los Angeles-class attack submarines have been in three major generations, starting with the 31 boats of the SSN-688 design, beginning with USS Los Angeles (SSN-688), commissioned in 1971. A number of this group have been decommissioned.

The 23 boats, from SSN 719 onward, added vertical launch system tubes, primarily for land attack BGM-109 Tomahawk cruise missiles. The final 31 boats (Improved Los Angeles-class), also called "Improved 688i", have improved under-ice capability, better electronics, and are quieter.

While the Seawolf-class was to have been the successor to the Los Angeles boats, it was optimized for blue-ocean, Cold War operation, and was a very large, expensive boat. Its construction was capped at three vessels, and the new U.S. attack submarine is the Virginia-class, designed to be more modular for different roles and more capable in the littoral than the Seawolves.

Intelligence and special operations

U.S. submarines had additional, still largely secret, and critical intelligence collection roles during the Cold War. Their use as intelligence platforms is one of their major roles today.


The very small Project 1910 Kashalot-class/NATO: Uniform-class submarine appear to be for intelligence misisons.

United States

In general, one U.S. submarine has been lengthened and assigned to largely classified duties, involving both intelligence collection and special operations force delivery. The current U.S. vessel is the USS Jimmy Carter, the third boat of the Seawolf-class attack submarine. Previous special operations boats included USS Parche and USS Halibut.

Post Cold War

With the end of the Cold War, roles have changed. Submarines still are important intelligence collection platforms, and can deliver United States Navy SEALs and other special operations forces. They can fire cruise missiles at shore targets; the older ballistic missile submarines have been modified to carry very large numbers of cruise missiles, and launch swimmer delivery vehicles. The first four Ohio class SSBNs have been converted in this manner, and are now designated SSGN.

U.S., U.K., and Soviet submarines were optimized for "blue water" Cold War operations. Likely conflicts, however, are likely littoral warfare in the "green water" shallows, especially in confined waters such as the Persian Gulf. Battery-operated, and newer types using air-independent propulsion, submarines represent a threat in a confined navigational channel, where they can stay silently on the bottom; indeed, slow, but ultraquiet submarines for such water are a major concern.

An example of the challenges here is the cancellation of the first set of ASW modules for the U.S. Navy Littoral Combat Ship, with a redesign in process. Intensive research is underway to find such submarines; a number of measurement and signature intelligence techniques are being explored, including magnetic MASINT and acoustic MASINT.


  1. Atlantis Submarines-The Story of Atlantis Submarines A civilian submarines tour service.
  2. U.S. Submarines-Submarines This webpage shows various civil submarines, such as luxury subs and tourist subs, are available to the wealthy public.
  3. More information on Civilian submarines and submersibles.
  4. Subs Become a Nuisance
  5. "New Subs Are Undersea Aircraft" , June 1949, Popular Science, p. 102
  6. Submarines: History - How They Work - Introduction
  7. Submarines: History - How They Work - Introduction
  8. USS Plunger (Submarine, built under 1895 contract, but not accepted for service). United States Navy (September 4, 1895). Retrieved on 2008-08-24.
  9. USS Plunger (Submarine # 2), 1903-1922, United States Navy. Retrieved on 2008-08-24.
  10. A few unsuccessful Soviet designs used conventional power and were designated SSB
  11. Also often written Granit