HISTORY OF SUBMARINE (PART-II)

 SUBMARINES TECHNOLOGY 

 Before and during World War II, the primary role of the submarine was anti-surface ship warfare. Submarines would attack either on the surface using deck guns, or submerged using torpedoes. They were particularly effective in sinking Allied transatlantic shipping in both World Wars, and in disrupting Japanese supply routes and naval operations in the Pacific in World War II.

Mine-laying submarines were developed in the early part of the 20th century. The facility was used in both World Wars. Submarines were also used for inserting and removing covert agents and military forces in special operations, for intelligence gathering, and to rescue aircrew during air attacks on islands, where the airmen would be told of safe places to crash-land so the submarines could rescue them. Submarines could carry cargo through hostile waters or act as supply vessels for other submarines.

Submarines could usually locate and attack other submarines only on the surface, although HMS Venturer managed to sink U-864 with a four torpedo spread while both were submerged. The British developed a specialized anti-submarine submarine in WWI, the R class. After WWII, with the development of the homing torpedo, better sonar systems, and nuclear propulsion, submarines also became able to hunt each other effectively.

The development of submarine-launched ballistic missile 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.

The primary defense of a submarine lies in its ability to remain concealed in the depths of the ocean. Early submarines could be detected by the sound they made. Water is an excellent conductor of sound (much better than air), and submarines can detect and track comparatively noisy surface ships from long distances. Modern submarines are built with an emphasis on stealth. Advanced propeller designs, extensive sound-reducing insulation, and special machinery help a submarine remain as quiet as ambient ocean noise, making them difficult to detect. It takes specialized technology to find and attack modern submarines.

Active sonar uses the reflection of sound emitted from the search equipment to detect submarines. It has been used since WWII by surface ships, submarines and aircraft (via dropped buoys and helicopter "dipping" arrays), but it reveals the emitter's position, and is susceptible to counter-measures.

A concealed military submarine is a real threat, and because of its stealth, can force an enemy navy to waste resources searching large areas of ocean and protecting ships against attack. This advantage was vividly demonstrated in the 1982 Falklands War when the British nuclear-powered submarine HMS Conqueror sank the Argentine cruiser General Belgrano. After the sinking the Argentine Navy recognized that they had no effective defense against submarine attack, and the Argentine surface fleet withdrew to port for the remainder of the war, though an Argentine submarine remained at sea.

Civilian

Although the majority of the world's submarines are military, there are some civilian submarines, which are used for tourism, exploration, oil and gas platform inspections, and pipeline surveys. Some are also used in illegal activities.

The Submarine Voyage ride opened at Disneyland in 1959, but although it ran under water it was not a true submarine, as it ran on tracks and was open to the atmosphere.[] The first tourist submarine was Auguste Piccard, which went into service in 1964 at Expo64.[] By 1997 there were 45 tourist submarines operating around the world.[51] Submarines with a crush depth in the range of 400–500 feet (120–150 m) are operated in several areas worldwide, typically with bottom depths around 100 to 120 feet (30 to 37 m), with a carrying capacity of 50 to 100 passengers.

In a typical operation a surface vessel carries passengers to an offshore operating area and loads them into the submarine. The submarine then visits underwater points of interest such as natural or artificial reef structures. To surface safely without danger of collision the location of the submarine is marked with an air release and movement to the surface is coordinated by an observer in a support craft.

A recent development is the deployment of so-called narco-submarines by South American drug smugglers to evade law enforcement detection.[] Although they occasionally deploy true submarines, most are self-propelled semi-submersibles, where a portion of the craft remains above water at all times. In September 2011, Colombian authorities seized a 16-meter-long submersible that could hold a crew of 5, costing about $2 million. The vessel belonged to FARC rebels and had the capacity to carry at least 7 tonnes of drugs.

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 its displacement of water. To control their displacement and weight, submarines have ballast tanks, which can hold varying amounts of water and air.

For general submersion or surfacing, submarines use the main ballast tanks (MBTs), which are ambient pressure tanks, filled with water to submerge, or with air to surface. While submerged, MBTs generally remain flooded, which simplifies their design,[] and on many submarines these tanks are a section of the space between the light hull and the pressure hull. For more precise control of depth, submarines use smaller depth control tanks (DCTs)—also called hard tanks (due to their ability to withstand higher pressure), or trim tanks. These are variable buoyancy pressure vessels, a type of buoyancy control device. The amount of water in depth control tanks can be adjusted to hydrostatically change depth or to maintain a constant depth as outside conditions (mainly water density) change.[] Depth control tanks may be located either near the submarine's center of gravity, to minimise the effect on trim, or separated along the length of the hull so they can also be used to adjust static trim by transfer of water between them.

When submerged, the water pressure on a submarine's hull can reach 4 MPa (580 psi) for steel submarines and up to 10 MPa (1,500 psi) for titanium submarines like K-278 Komsomolets, while interior pressure remains relatively unchanged. This difference results in hull compression, which decreases displacement. Water density also marginally increases with depth, as the salinity and pressure are higher.[] This change in density incompletely compensates for hull compression, so buoyancy decreases as depth increases. A submerged submarine is in an unstable equilibrium, having a tendency to either sink or float to the surface. Keeping a constant depth requires continual operation of either the depth control tanks or control surfaces.

Submarines in a neutral buoyancy condition are not intrinsically trim-stable. To maintain desired longitudinal trim, submarines use forward and aft trim tanks. Pumps move water between the tanks, changing weight distribution and pitching the sub up or down. A similar system may be used to maintain transverse trim.

CONTROL SURFACES

The hydrostatic effect of variable ballast tanks is not the only way to control the submarine underwater. Hydrodynamic maneuvering is done by several control surfaces, collectively known as diving planes or hydroplanes, which can be moved to create hydrodynamic forces when a submarine moves longitudinally at sufficient speed. In the classic cruciform stern configuration, the horizontal stern planes serve the same purpose as the trim tanks, controlling the trim. Most submarines additionally have forward horizontal planes, normally placed on the bow until the 1960s but often on the sail on later designs, where they are closer to the center of gravity and can control depth with less effect on the trim.

An obvious way to configure the control surfaces at the stern of a submarine is to use vertical planes to control yaw and horizontal planes to control pitch, which gives them the shape of a cross when seen from astern of the vessel. In this configuration, which long remained the dominant one, the horizontal planes are used to control the trim and depth and the vertical planes to control sideways maneuvers, like the rudder of a surface ship.

Alternatively, the rear control surfaces can be combined into what has become known as an x-stern or an x-rudder. Although less intuitive, such a configuration has turned out to have several advantages over the traditional cruciform arrangement. First, it improves maneuverability, horizontally as well as vertically.[clarification needed] Second, the control surfaces are less likely to get damaged when landing on, or departing from, the seabed as well as when mooring and unmooring alongside. Finally, it is safer in that one of the two diagonal lines can counteract the other with respect to vertical as well as horizontal motion if one of them accidentally gets stuck.

The x-stern was first tried in practice in the early 1960s on the USS Albacore, an experimental submarine of the US Navy. While the arrangement was found to be advantageous, it was nevertheless not used on US production submarines that followed due to the fact that it requires the use of a computer to manipulate the control surfaces to the desired effect. Instead, the first to use an x-stern in standard operations was the Swedish Navy with its Sjöormen class, the lead submarine of which was launched in 1967, before the Albacore had even finished her test runs.[] Since it turned out to work very well in practice, all subsequent classes of Swedish submarines (Näcken, Västergötland, Gotland, and Blekinge class) have or will come with an x-rudder.

The Kockums shipyard responsible for the design of the x-stern on Swedish submarines eventually exported it to Australia with the Collins class as well as to Japan with the Sōryū class. With the introduction of the type 212, the German and Italian Navies came to feature it as well. The US Navy with its Columbia class, the British Navy with its Dreadnought class, and the French Navy with its Barracuda class are all about to join the x-stern family. Hence, as judged by the situation in the early 2020s, the x-stern is about to become the dominant technology.

When a submarine performs an emergency surfacing, all depth and trim control methods are used simultaneously,[citation needed] together with propelling the boat upwards. Such surfacing is very quick, so the sub may even partially jump out of the water, potentially damaging submarine systems.

Modern submarines are cigar-shaped. This design, also used in very early submarines, is sometimes called a "teardrop hull". It reduces hydrodynamic drag when the sub is 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), 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. USS Albacore (AGSS-569) was a unique research submarine that pioneered the American version of the teardrop hull form (sometimes referred to as an "Albacore hull") of modern submarines. 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 and efficient use of materials to withstand external pressure as it gives the most internal volume for structural weight and is the most efficient shape to avoid buckling instability in compression. A frame is usually affixed to the outside of 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 standard submarine accommodates the periscope and electronics masts, which can include radio, radar, electronic warfare, and other systems. It might also include a 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" or "fin". 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.

Modern submarines and submersibles usually have, as did the earliest models, a single hull. Large submarines generally have an additional hull or hull sections outside. This external hull, which actually forms the shape of submarine, is called the outer hull (casing in the Royal Navy) or light hull, as it does not have to withstand a pressure difference. Inside the outer hull there is a strong hull, or pressure hull, which withstands sea pressure and has normal atmospheric pressure inside.

As early as World War I, it was realized that the optimal shape for withstanding pressure conflicted with the optimal shape for seakeeping and minimal drag at the surface, and construction difficulties further complicated the problem. This was solved either by a compromise shape, or by using two layered hulls: the internal strength hull for withstanding pressure, and an external fairing for hydrodynamic shape. Until the end of World War II, most submarines had an additional partial casing on the top, bow and stern, built of thinner metal, which was flooded when submerged. Germany went further with the Type XXI, a general predecessor of modern submarines, in which the pressure hull was fully enclosed inside the light hull, but optimized for submerged navigation, unlike earlier designs that were optimized for surface operation.

After World War II, approaches split. The Soviet Union changed its designs, basing them on German developments. All post-World War II heavy Soviet and Russian submarines are built with a double hull structure. American and most other Western submarines switched to a primarily single-hull approach. They still have light hull sections in the bow and stern, which house main ballast tanks and provide a hydrodynamically optimized shape, but the main cylindrical hull section has only a single plating layer. Double hulls are being considered for future submarines in the United States to improve payload capacity, stealth and range.

The pressure hull is generally constructed of thick high-strength steel with a complex structure and high strength reserve, and is separated by watertight bulkheads into several compartments. There are also examples of more than two hulls in a submarine, like the Typhoon class, which has two main pressure hulls and three smaller ones for control room, torpedoes and steering gear, with the missile launch system between the main hulls, all surrounded and supported by the outer light hydrodynamic hull. When submerged the pressure hull provides most of the buoyancy for the whole vessel.

The dive depth cannot be increased easily. Simply making the hull thicker increases the structural weight and requires reduction of onboard equipment weight, and increasing the diameter requires a proportional increase in thickness for the same material and architecture, ultimately resulting in a pressure hull that does not have sufficient buoyancy to support its own weight, as in a bathyscaphe. This is acceptable for civilian research submersibles, but not military submarines, which need to carry a large equipment, crew, and weapons load to fulfill their function. Construction materials with greater specific strength and specific modulus are needed.

WWI submarines had hulls of carbon steel, with a 100-metre (330 ft) maximum depth. During WWII, high-strength alloyed steel was introduced, allowing 200-metre (660 ft) depths. High-strength alloy steel remains the primary material for submarines today, with 250–400-metre (820–1,310 ft) depths, which cannot be exceeded on a military submarine without design compromises. To exceed that limit, a few submarines were built with titanium hulls. Titanium alloys can be stronger than steel, lighter, and most importantly, have higher immersed specific strength and specific modulus. Titanium is also not ferromagnetic, important for stealth. Titanium submarines were built by the Soviet Union, which developed specialized high-strength alloys. It has produced several types of titanium submarines. Titanium alloys allow a major increase in depth, but other systems must be redesigned to cope, so test depth was limited to 1,000 metres (3,300 ft) for the Soviet submarine K-278 Komsomolets, the deepest-diving combat submarine. An Alfa-class submarine may have successfully operated at 1,300 metres (4,300 ft),[70] though continuous operation at such depths would produce excessive stress on many submarine systems. Titanium does not flex as readily as steel, and may become brittle after many dive cycles. Despite its benefits, the high cost of titanium construction led to the abandonment of titanium submarine construction as the Cold War ended. Deep-diving civilian submarines have used thick acrylic pressure hulls. Although the specific strength and specific modulus of acrylic are not very high, the density is only 1.18g/cm3, so it is only very slightly denser than water, and the buoyancy penalty of increased thickness is correspondingly low.

The deepest deep-submergence vehicle (DSV) to date is Trieste. On 5 October 1959, Trieste departed San Diego for Guam aboard the freighter Santa Maria to participate in Project Nekton, a series of very deep dives in the Mariana Trench. On 23 January 1960, Trieste reached the ocean floor in the Challenger Deep (the deepest southern part of the Mariana Trench), carrying Jacques Piccard (son of Auguste) and Lieutenant Don Walsh, USN.[71] This was the first time a vessel, crewed or uncrewed, had reached the deepest point in the Earth's oceans. The onboard systems indicated a depth of 11,521 metres (37,799 ft), although this was later revised to 10,916 metres (35,814 ft) and more accurate measurements made in 1995 have found the Challenger Deep slightly shallower, at 10,911 metres (35,797 ft).

Building a pressure hull is difficult, as it must withstand pressures at its required diving depth. When the hull is perfectly round in cross-section, the pressure is evenly distributed, and causes only hull compression. If the shape is not perfect, the hull deflects more in some places and buckling instabity is the usual failure mode. Inevitable minor deviations are resisted by stiffener rings, but even a one-inch (25 mm) deviation from roundness results in over 30 percent decrease of maximal hydrostatic load and consequently dive depth.[72] The hull must therefore be constructed with high precision. All hull parts must be welded without defects, and all joints are checked multiple times with different methods, contributing to the high cost of modern submarines. (For example, each Virginia-class attack submarine costs US$2.6 billion, over US$200,000 per ton of displacement.