A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fins are also used to increase surface areas for heat transfer purposes, or simply as ornamentation.
A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, and with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, such a device was called an automotive, automobile, locomotive, or fish torpedo; colloquially a fish. The term torpedo originally applied to a variety of devices, most of which would today be called mines. From about 1900, torpedo has been used strictly to designate a self-propelled underwater explosive device.
Supercavitation is the use of a cavitation bubble to reduce skin friction drag on a submerged object and enable high speeds. Applications include torpedoes and propellers, but in theory, the technique could be extended to an entire underwater vessel.
The Douglas TBD Devastator was an American torpedo bomber of the United States Navy. Ordered in 1934, it first flew in 1935 and entered service in 1937. At that point, it was the most advanced aircraft flying for the Navy; however, by the time of the US entry into World War 2, the TBD was already outdated.
The Douglas XTB2D Skypirate was a torpedo bomber intended for service with the United States Navy's Midway- and Essex-class aircraft carriers; it was too large for earlier decks. Two prototypes were completed, but the dedicated torpedo bomber was becoming an outdated concept, and with the end of World War II, the type was deemed unnecessary and cancelled.
A diver propulsion vehicle (DPV), also known as an underwater propulsion vehicle, sea scooter, underwater scooter, or swimmer delivery vehicle (SDV) by armed forces, is an item of diving equipment used by scuba divers to increase range underwater. Range is restricted by the amount of breathing gas that can be carried, the rate at which that breathing gas is consumed, and the battery power of the DPV. Time limits imposed on the diver by decompression requirements may also limit safe range in practice. DPVs have recreational, scientific and military applications.
A bouncing bomb is a bomb designed to bounce to a target across water in a calculated manner to avoid obstacles such as torpedo nets, and to allow both the bomb's speed on arrival at the target and the timing of its detonation to be predetermined, in a similar fashion to a regular naval depth charge. The inventor of the first such bomb was the British engineer Barnes Wallis, whose "Upkeep" bouncing bomb was used in the RAF's Operation Chastise of May 1943 to bounce into German dams and explode underwater, with an effect similar to the underground detonation of the later Grand Slam and Tallboy earthquake bombs, both of which he also invented.
The SPP-1 underwater pistol was made in the Soviet Union for use by Soviet frogmen as an underwater firearm. It was developed in the late 1960s and accepted for use in 1975. Under water, ordinary-shaped bullets are inaccurate and very short-range. As a result, this pistol fires a round-based 4.5 millimetres (0.18 in) caliber steel dart about 115 millimetres (4.5 in) long, weighing 12.8 grams (0.45 oz), which has longer range and more penetrating power than speargun spears. The complete cartridge is 145 millimetres (5.7 in) long and weighs 17.5 grams (0.62 oz).
The VA-111 Shkval torpedo and its descendants are supercavitating torpedoes originally developed by the Soviet Union. They are capable of speeds in excess of 200 knots.
The Hoot is an Iranian supercavitation torpedo claimed to travel at approximately 360 km/h (220 mph), several times faster than a conventional torpedo. It was claimed to have been successfully test-fired from a surface ship against a dummy submarine during the Iranian military exercise "Great Prophet" on 2 April 2006 and 3 April 2006. Iran test-fired the torpedo within its territorial waters in the Strait of Hormuz in May 2017.
The Type 039 submarine is a class of diesel-electric submarines of the People's Liberation Army Navy. The class is the first diesel-electric submarine to be made in China and also the first Chinese made diesel-electric submarine to use the teardrop hull shape. Altogether thirteen vessels were completed to the Song Class design between 1999 and 2006, with three variants as the type developed.
Underwater speed record include records for submarines, autonomous underwater vehicles, and torpedoes. As these are typically for military vehicles, most are unconfirmed.
A wet sub is a type of underwater vehicle, either a submarine or a submersible, that does not provide a dry environment for its occupants. It is also described as an underwater vehicle where occupants are exposed to ambient environment during operations. The watercraft is classified as medium-sized or small vessel. This type of submarine differs from other underwater personal transport devices by the fact that it has a hull around it and it is not a "bare bones" design.
An underwater firearm is a firearm designed for use underwater. Underwater firearms or needleguns usually fire flechettes or spear-like bolts instead of standard bullets. These may be fired by pressurised gas.
The Larami Corporation was a toy company established by David W. Ring in Philadelphia, Pennsylvania, in 1959. It produced licensed toys based on movies and television shows. Often low-quality, these were manufactured in Hong Kong and Japan for sale on grocery store toy aisle racks for under a dollar.
The TR-1700 is a class of diesel-electric patrol submarines built by Thyssen Nordseewerke for the Argentine Navy in the 1980s, with two submarines completed. These ships are amongst the largest submarines built in Germany since World War II and are among the fastest diesel-electric submarines in the world. ARA San Juan was lost on 17 November 2017, leaving ARA Santa Cruz as the only remaining submarine of this class. As of 2020, the refit of Santa Cruz has been reported cancelled leaving the entire class inactive.
The Great Lakes XTBG-1 was an American prototype torpedo bomber, intended for service in the United States Navy as part of that service's plan to modernise its aerial striking force in the mid-1930s. The XTBG-1 was outperformed by the competing TBD Devastator, however, in addition to having instability problems and only a single prototype of the three-seat design was constructed during 1935.
The explosive motorboat MT also known as barchino, was a series of small explosive motor boats developed by the Italian Royal Navy, which was based on its predecessors, the prototype boat MA and the MAT, an airborne prototype. Explosive motorboats were designed to make a silent approach to a moored warship, set a collision course and run into full gear until the last 200 or 100 yards to the target, when the pilot would eject after blocking the rudder. At impact, the hull would be broken amidships by a small explosive charge, sinking the boat and the warhead, which was fitted with a water-pressure fuse set to go off at a depth of one metre.
A nuclear torpedo is a torpedo armed with a nuclear warhead. The idea behind the nuclear warheads in a torpedo was to create a much bigger explosive blast. Later analysis suggested that smaller, more accurate, and faster torpedoes were more efficient and effective.
The Superkavitierender Unterwasserlaufkörper was a German close-range supercavitating torpedo technology demonstrator designed by the Diehl BGT Defence and developed in cooperation with the German Navy. The supercavitating torpedo for a "close-range defense of underwater targets" was presented to the public in 2005 as a prototype, but it never went into development and procurement.
VA-111 Shkval, 1977
Hoot, 2006
Superkavitierender Unterwasserlaufkörper (Supercavitating underwater-travelling munition) Barracuda, 2005 prototype
Unnamed prototype, mentioned 2004 [1] 
