Submarine

In modern context, a submarine is a warship that routinely moves, detects targets, and attack 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. "We hide with pride", and the "silent service", are informal and formal mottoes of undersea warfare.

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.

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 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

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.

In the Second World War, however, submarines had a vital role, German 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 tracking transmissions and reading encrypted messages. Eventually, roughly 75 percent of U-boat sailors died in action, or, in U.S. tradition, "on eternal patrol". Both of Doenitz's sons died on missions.

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.

The U.S. submarine 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.

First technological revolution: nuclear propulsion

In 1955, USS Nautilus' (SS-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 propulsion 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 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

Second techological revolution: electronic sensors 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 SONARs or 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 missile submarines

The next major development certainly let submarines share, and possibly exceed, the previous queens of the sea, aircraft carriers. In the late fifties, ballistic missiles, which could be fired from a submerged submarine, started with a range of 1000 miles. Modern missiles have the range 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.

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.

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.

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.

U.S., U.K., and Soviet submarines were optimized for "blue water" Cold War operations. Conflict, however, is now in the "green water" shallow littorals not far off coasts, especially in confined waters such as the Persian Gulf. Even battery-operated submarines represent a threat in a confined navigational channel, where they can stay silently on the bottom. Intensive research is underway to find such submarines; a number of measurement and signature intelligence techniques are being explored, including geophysical MASINT and acoustic MASINT.