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Submarines Knowledge

The term submarine most commonly refers to large manned autonomous vessels, however historically or more casually, submarine can also refer to medium sized or smaller vessels, (midget submarines, wet subs), Remotely Operated Vehicles or robots. The word submarine was originally an adjective meaning "under the sea", and so consequently other uses such as 'submarine engineering' or 'submarine cable' may not actually refer to submarines at all. Submarine was shortened from the term 'submarine boat'.

Submarines are referred to as "boats" for historical reasons because vessels deployed from a ship are referred to as boats. The first submarines were launched in such a manner. The English term U-Boat for a German submarine comes from the German word for submarine, `U-Boot`, itself an abbreviation for Unterseeboot ('undersea boat').

Although experimental submarines had been built before, submarine design took off during the 19th century. Submarines were first widely used in World War I, and feature in many large navies. Military usage ranges from attacking enemy ships or submarines, aircraft carrier protection, blockade running, ballistic missile submarines as part of a nuclear strike force, reconnaissance and covert insertion of special forces. Civilian uses for submarines include marine science, salvage, exploration and facility inspection/maintenance. Submarines can also be specialised to a function such as search and rescue, or undersea cable repair. Submarines can also be used in tourism and for academic research.

Submarines have one of the largest ranges in capabilities of any vessel, ranging from small autonomous or one- or two-man vessels operating for a few hours, to vessels which can remain submerged for 6 months such as the Russian Typhoon class. Submarines can work at greater depths than are survivable or practical for human divers. Modern deep diving submarines are derived from the bathyscaphe, which in turn was an evolution of the diving bell.

Most large submarines comprise a cylindrical body with conical ends and a vertical structure, usually located amidships, which houses communications and sensing devices as well as periscopes. In modern submarines this structure is the "sail" in American usage ("fin" in European usage). A "conning tower" was a feature of earlier designs: a separate pressure hull above the main body of the boat that allowed the use of shorter periscopes. There is a propeller (or pump jet) at the rear and various hydrodynamic control fins as well as ballast tanks. Smaller, deep diving and specialty submarines may deviate significantly from this traditional layout. info sourced : http://en.wikipedia.org/wiki/Submarine

Until the development of the homing torpedo in World War Two, the primary role of the diesel/electric submarine was anti-ship warfare, inserting and removing covert agents and military forces, and intelligence-gathering and was generally not used against other submarines (although British developed an anti-submarine submarine in World War I, dubbed the "R1"). The impact-detonated torpedoes of the era were difficult to use against a submarine because they ran a fixed course at a fixed depth and were relatively easy for the small submarines to avoid with three dimensional maneuvers. Submarines were also used in limited roles for artillery support or raids, and rescuing aircrews during large-scale air attacks on islands, where the aircrewmen would be told of safe places to crash-land damaged aircraft so the submarine crew could rescue them.

With the development of the homing torpedo, better sonar systems, and nuclear propulsion, submarines also became able to effectively hunt each other as well as surface ships. The development of submarine-launched nuclear missiles and submarine-launched cruise missiles gave submarines a substantial and long-ranged ability to attack both land and sea targets with a variety of weapons ranging from cluster bombs to nuclear weapons.

Mine laying submarines were developed in the early part of the 20th century. The facility has been used in both World Wars. Such capabilities continue today.

The primary defensive power of a submarine lies in its ability to remain concealed in the depths of the ocean. Modern submarines are built with an emphasis on stealth. Advanced propeller designs, extensive sound-reducing insulation, and special machinery allow a submarine to be as quiet as ambient ocean noise, making them extremely difficult to detect. Such submarines can launch an attack on land targets, surface ships, and other submarines from seemingly nowhere, and require specialized equipment to find and attack in retaliation. Water is an excellent conductor of sound, and submarines have excellent sonars that can detect and track comparatively noisy surface ships from long distances. This allows an attacking sub, at its discretion, to quietly maneuver to and attack from the best possible position at the best possible time.

A concealed military submarine is a real threat and, because of its stealth, it can force an enemy navy to waste resources searching large areas of ocean and protecting all ships against possible attack, while in reality only threatening a small area. This advantage was vividly demonstrated in the 1982 Falklands War when the British SSN HMS Conqueror sank the Argentine cruiser General Belgrano. After the sinking the Argentine Navy realized that they were vulnerable to submarine attack, and that they had no defense from it. Thus the Argentinian surface fleet withdrew to port for the remainder of the war, though an Argentinian submarine remained at sea.

During World War II some military submarines were used as supply vessels for U-boats.

Anti-submarine net

One of the defenses against submarines is an antisubmarine net that blocks the passage, e.g. at the entrance of a harbor. It can sometimes be lowered to let friendly ships pass. See e.g. antisubmarine nets at Pearl Harbor. See also net laying ship.

Although the majority of the world's submarines are military ones, there are some civil submarines. They have a variety of uses, including tourism, exploration, oil and gas platform inspections and pipeline surveys.

A semi-civilian use was the adaption of U-boats for cargo carrying during both the First and Second World Wars. Another is that of submarine crew rescue.

Sensors

A submarine will have a range of sensor types that depends on its purpose. Modern military submarines rely almost entirely on an extremely sensitive suite of passive and active sonars to find their prey. Active sonar relies on an audible "ping" to generate echoes revealing objects around the transmitting submarine. Active systems are rarely used, as the transmitting submarine will invariably reveal its own position to its target. Passive sonar is literally a set of extremely sensitive hydrophones set into the submarine's hull or trailed behind said submarine in a towed array, generally several hundred feet long, if not more. The towed array is the mainstay of NATO submarine detection systems, as it reduces the amount of flow noise that is heard by the operators. Hull mounted sonar is employed to back up the towed array, and in confined coastal waters where a towed array could be fouled by sea floor obstacles.

Submarines also carry radar equipment for detection of surface ships and aircraft. Again, sub captains are more likely to use radar detection gear rather than active radar to detect targets, as radar energy can be detected far beyond its own return range, revealing the transmitting submarine's position. Periscopes are hardly ever used except to take position fixes and to verify the identity of a contact.

Civilian submarines, such as Alvin or the Russian Mir submersibles, rely on small active sonar sets and viewing ports to navigate. Light does not penetrate beyond about 300 feet, so high intensity lights must be carried to illuminate the area around the submersible.

Navigation

Although early submarines had very little in the way of navigation aids, modern submarines have a variety of navigation systems. Modern military submarines use an inertial guidance system for navigation while submerged, but drift error unavoidably builds up over time. To counter this, the Global Positioning System will occasionally be used to obtain an accurate position. The periscope - a retractable tube with prisms allowing a view to the surface - is only used occasionally in modern submarines, since the range of visibility is short. The Virginia-class submarines and Astute Class submarines have "photonics masts" rather than hull-penetrating optical tube periscopes. These masts must still be hoisted above the surface, and employ electronic sensors for visible light, infrared, laser range-finding, and electromagnetic surveillance.

Communication

Military submarines have several systems for communicating with distant command centers or other ships. One is the VLF radio, which can reach a submarine either on the surface or submerged up to a fairly shallow depth, usually less than 250 feet or so. ELF frequencies can reach a submarine at much greater depths, but has a very low bandwidth and is generally only used to call a submerged sub to a shallower depth where VLF signals can reach. A submarine also has the option of floating a long, buoyant wire to a shallower depth, allowing VLF transmissions to be made by even a deeply submerged boat.

By extending a radio mast, a submarine can also use a "burst transmission" technique. A burst transmission takes only a fraction of a second, minimizing a submarine's risk of detection. To communicate with other submarines, a system known as Gertrude is used. Gertrude is basically a sonar telephone. Voice communication from one submarine is transmitted by low power speakers into the water, where it is detected by passive sonars on the receiving submarine. The range of this system is probably very short, and using it radiates sound into the water, which can be heard by enemy submarines, surface ships and aircraft.

Civilian submarines can use similar, albeit less powerful systems to communicate with support ships or other submersibles in the area.

Command and control

All submarines need facilities to control their motion. Military submarines also need facilities to operate their sensors and weapons.

info sourced : http://en.wikipedia.org/wiki/Submarine