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submarine iNFO:
A model of Günther Prien's U-47, German WWII Type VII diesel-electric hunter
Prior to the development of the homing torpedo in World War II, the primary role of the diesel/electric submarine was anti-surface ship warfare, inserting and removing covert agents and military forces, and intelligence-gathering. Until that time they were generally not used against other submarines (although British developed a specialised anti-submarine submarine in World War I, the R class). 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.
[edit] 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 antisubmarine nets at Pearl Harbor or net laying ship.
[edit] Civil uses
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 transport during WWI and WWII.
[edit] Technology
[edit] Submersion and trimming
Control surfaces
HMS Astute is one of the most advanced nuclear submarines in the world.[1]
All surface ships, as well as surfaced submarines, are in a positively buoyant condition, weighing less than the volume of water they would displace if fully submerged. To submerge hydrostatically, a ship must have negative buoyancy, either by increasing its own weight or decreasing displacement of the water. To control their weight, submarines have ballast tanks, which can be filled with outside water or pressurized air.
For general submersion or surfacing, submarines use the forward and aft tanks, called Main Ballast Tanks or MBTs, which are filled with water to submerge, or filled with air to surface. Under submerged conditions, MBTs generally remain flooded, which simplifies their design, and on many submarines these tanks are a section of interhull space. For more precise and quick control of depth, submarines use smaller Depth Control Tanks or DCTs, also called hard tanks due to their ability to withstand higher pressure. The amount of water in depth control tanks can be controlled either to reflect changes in outside conditions or change depth. Depth control tanks can be located either near the submarine's center of gravity, or separated along the submarine body to prevent affecting trim.
When submerged, the water pressure on submarine's hull can reach 4 MPa for steel submarines and up to 10 MPa for titanium submarines like Komsomolets, while interior pressure remains unchanged. This difference results in hull compression, which decreases displacement. Water density also increases, as the salinity and pressure are higher, but this does not compensate for hull compression, so buoyancy decreases as depth increases. A submerged submarine is in an unstable equilibrium, having a tendency to either fall or float to the surface. Keeping a constant depth requires continual operation of either the depth control tanks or control surfaces.[2][verification needed][dubious – discuss]
Submarines in a neutral buoyancy condition are not intrinsically trim-stable. To maintain desired trim, submarines use forward and aft trim tanks. Pumps can move water between these, changing weight distribution, creating a moment pointing the sub up or down. A similar system is sometimes used to maintain stability.
Sail of the French nuclear submarine Casabianca; note the diving planes, camouflaged masts, periscope, electronic warfare masts, door and windows.
The hydrostatic effect of variable ballast tanks is not the only way to control the submarine underwater. Hydrodynamic maneuvering is done by several surfaces, which can be moved to create hydrodynamic forces when a submarine moves at sufficient speed. The stern planes, located near the propeller and normally horizontal, serve the same purpose as the trim tanks, controlling the trim, and are commonly used, while other control surfaces may not be present on many submarines. The fairwater planes on the sail and/or bow planes on the main body, both also horizontal, are closer to the centre of gravity, and are used to control depth with less effect on the trim.
When a submarine performs an emergency surfacing, all depth and trim methods are used simultaneously, together with propelling the boat upwards. Such surfacing is very quick, so the sub may even partially jump out of the water, but it may inflict serious damage on submarine systems.
[edit] Submarine hull
Main article: Submarine hull
[edit] Overview
The Los Angeles class attack submarine USS Greeneville in dry dock, showing typical cigar-shaped hull.
Modern submarines are cigar-shaped. This design, visible in early submarines (see below) is sometimes called a "teardrop hull". It reduces the hydrodynamic drag when submerged, but decreases the sea-keeping capabilities and increases drag while surfaced. Since the limitations of the propulsion systems of early submarines forced them to operate surfaced most of the time, their hull designs were a compromise. Because of the slow submerged speeds of those subs, usually well below 10 kt (18 km•h-1), the increased drag for underwater travel was acceptable. Late in World War II, when technology allowed faster and longer submerged operation and increased aircraft surveillance forced submarines to stay submerged, hull designs became teardrop shaped again to reduce drag and noise. On modern military submarines the outer hull is covered with a layer of sound-absorbing rubber, or anechoic plating, to reduce detection.
The occupied pressure hulls of deep diving submarines such as DSV Alvin are spherical instead of cylindrical. This allows a more even distribution of stress at the great depth. A titanium frame is usually affixed to the pressure hull, providing attachment for ballast and trim systems, scientific instrumentation, battery packs, syntactic flotation foam, and lighting.
A raised tower on top of a submarine accommodates the periscope and electronics masts, which can include radio, radar, electronic warfare, and other systems including the snorkel mast. In many early classes of submarines (see history), the Control Room, or "Conn", was located inside this tower, which was known as the "conning tower". Since then, the Conn has been located within the hull of the submarine, and the tower is now called the "sail". The Conn is distinct from the "bridge", a small open platform in the top of the sail, used for observation during surface operation.
"Bathtubs" are related to conning towers but are used on smaller submarines. The bathtub is a metal cylinder surrounding the hatch that prevents waves from breaking directly into the cabin. It is needed because surfaced submarines have limited freeboard, that is, they lie low in the water. Bathtubs help prevent swamping the vessel.
[edit] Single / double hull
U-995, Type VIIC/41 U-Boat of WWII, showing the typical combination of ship-like non-watertight outer hull with bulky strong hull below
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