Encyclopedia
A
submarine is a specialized watercraft that can operate
underwater. Submarines, first widely used in
World War I, are used by all major
navies today, especially the
American,
Russian and
British navies. Civilian submarines and
submersibles are used for marine and
freshwater science and for work at depths too great for human divers.
Submarines are always referred to as boats. The term
U-Boat is sometimes used for German submarines in
English. This comes from the
German word for submarine, 'U-Boot', itself an abbreviation for
Unterseeboot .
Submarines encompass one of the largest ranges in capabilities of any vessel. They range from small two-man vessels that can examine the sea floor for a few hours to the
Russian
Typhoon class, which can remain submerged for half a year and carry enough nuclear missiles to destroy hundreds of
cities. There are also specialized submarines such as rescue submarines and tiny one-person human powered subs intended for competitions between
universities. An older device for use in underwater exploration, salvage, construction and rescue is the
diving bell.
The word
submarine was originally an adjective meaning "under the sea". Some firms who make
diving gear but not parts for submarines, called their work "submarine engineering". "Submarine" as a noun meaning a submersible craft originated as short for "submarine boat" and older books such as
Twenty Thousand Leagues Under the Sea is a classic science fiction [i] novel by French [i] wr ...
always use this term.
Civilian submarines and submersibles
Civilian submarines are usually much smaller than military submarines.
Tourist submarines work mainly in tropical resort areas or other areas with clear water and good visibility. By 1996 there were over fifty private submarines operating around the world, serving approximately two million passengers a year. Most of them carried between twenty-five and fifty passengers at a time and sometimes made ten or more dives per day. In design, these submarines borrow mainly from research subs, having large
portholes for passengers' viewing and often placing significant mechanical systems outside the hull to conserve interior space. Nonetheless, even aboard tourist submarines the seating can be rather cramped. They are mainly battery-powered and very slow.
As of January 2005, the largest tourist submarine in use was the
Atlantis XIV based out of
Waikiki beach. The largest
Atlantis-class submarine of its fleet, launched in 1994, can carry 64 passengers and 3 crew to 150 feet deep off the shores of
the island of O'ahu in
Hawai'i. There, tourists can view a great number of ocean specimens living around artificial
reefs.
In common usage, "submarine" means a ship that operates above and below the surface, untethered. Underwater vessels with limited mobility, intended to remain in one place during most of their use, such as those used for rescue, research or salvage purposes are usually called "
submersibles". Submersibles are typically transported to their area of operation by surface ships or large submarines and have a very short range. Many submersibles operate on a "tether" or "umbilical", remaining connected to a tender .
Bathyspheres are submersibles that lack self-propulsion and used for very deep diving. A predecessor of the bathysphere, the diving bell, consisted of a chamber with an open bottom, lowered into the water.
Bathyscaphes are self-propelled deep-diving submersibles reliant on a mother ship on the surface.
A fairly recent development, very small, unmanned submersibles called "marine remotely operated vehicles" are widely used today to work in water too deep or too dangerous for divers. For example, remotely operated vehicles repair offshore
petroleum platforms and attach cables to sunken ships to hoist them. A thick cable providing power and communications tethers these remotely operated vehicles to a control center on a ship. Operators on the ship see video images sent back from the robot and may control its propellers and manipulator arm. The wreck of the
Titanic was an Olympic class passenger liner [i] that became...
was explored by such a vehicle, as well as by a manned vessel.
Private individuals have designed, build and operated submarines for recreational use. One example is the K-250 submersible designed by George Kittredge. Its a one-person, 2.5 tonne, 1-ATM, dry submarine rated for a maximum depth of 250 feet. Claus Noerregaard and Peter Madsen from Copenhagen, Denmark have sucsesfully build a larger diesel-eletric submarine named "Kraka"
and operated it in the Baltic. Kraka is 42 feet long and displaces 6 tonnes. This submarine, based largely on military concepts, is one of very few seagoing privately built submarines. Built for coastal waters, the Kraka is rated for a maximum diving depth of 120 feet.
Military submarines
There are more military submarines in operation than civilian ones. Submarines are useful militarily because they are difficult to locate and difficult to destroy when deep below the surface. A great deal of attention in the design of a submarine is devoted to making it travel through the water as silently as possible in order to prevent its detection.
Sound travels underwater much more easily than light does, meaning that a submarine's sound is the feature most likely to allow its detection. Some submarines conceal their sound so well that they actually create a silent area in their environment, which can also be detected. If a submarine remains undetected, it is able to strike at close range.
Submersion and navigation
All surface ships, as well as surfaced submarines, are in positively
buoyant condition, weighing less than the water they displace. To submerge hydrostatically, a ship must gain negative buoyancy, either increasing its own weight or decreasing displacement of the water. To control their weight, submarines are equipped with ballast tanks, which can be filled with either 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 opened and completely filled with water to submerge, or filled by pressurized air to surface. Under submerged conditions, MBTs generally always stay flooded, which simplifies their design, so on many submarines these tanks are simply 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 submersion depth. Depth control tanks can be located either near the submarine's
centre of gravity, or separated along the submarine body to prevent affecting trim.
When submerged, the water pressure on submarine's hull can reach 3 MPa for steel submarines and up to 10 MPa for titanium submarines like
Komsomolets, while the pressure inside stays the same. 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 falls with depth. A submerged submarine is in an unstable equilibrium, having a tendency to either fall down to the ocean floor or float up to the surface. Keeping a constant depth requires continual operation of the depth control tanks.
Submarines in a neutral buoyancy condition are not intrinsically stable in trim. To sustain desired trim, submarines use specialized forward and aft trim tanks. Pumps can move water between these tanks, changing the weight distribution and therefore creating a momentum to turn the sub upwards or downwards. A similar system is sometimes used to maintain stability.
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 turned to create corresponding hydrodynamic forces when a submarine moves at sufficient speed. The stern planes, located near the propeller and normally oriented horizontally, 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 located 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 inflicts serious damage on some submarine systems, primarily pipes.
Modern 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 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.
Submarine hull
Modern submarines are usually
cigar-shaped. This design, already visible on very early submarines is called a "teardrop hull", and was patterned after the bodies of
whales. It significantly reduces the hydrodynamic drag on the sub when submerged, but decreases the sea-keeping capabilities and increases the drag while surfaced. Since the limitations of the propulsion systems of early military submarines forced them to operate on the surface most of the time, their hull designs were a compromise. Because of the slow submerged speeds of those subs, usually well below 10
kt , the increased drag for underwater travel was considered acceptable. Only late in World War II, when technology allowed faster and longer submerged operations and increased surveillance by enemy aircraft forced submarines to stay submerged, did hull designs become teardrop shaped again, to reduce drag and noise. On modern military submarines the outer hull is covered with a thick layer of special sound-absorbing
rubber, or anechoic plating, to make the submarine quieter.
A raised tower on top of a submarine accommodates the length of the
periscope and electronics masts, which can include
radio,
radar, electronic warfare, and other systems. In many early classes of submarines , the Control Room, or "Conn", was located inside this tower, which was known as the "
conning tower". Since that time, however, the Conn has been located within the hull of the submarine, and the tower is more commonly called the "sail" today. The Conn should not be confused with the "bridge", which is a small, open platform set into the top of the sail used for visual observation while operating on the surface. There may also be an additional closed platform below this with windows and wipers for bad weather.
Double hull
All small modern submarines and submersibles, as well as the oldest ones, have 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 or
light hull, as it does not have to hold any pressure difference. Inside the outer hull there is a strong hull, or
pressure hull, which withstands sea pressure and has normal atmospheric pressure inside.
Starting from the times of World War I it was realized that the optimal shape for withstanding pressure conflicted with optimal shape for seaworthiness and minimized water resistance, and construction difficulties further complicated the problem. This was solved either by a compromise shape, or by using two hulls shapes, internal for holding pressure, and external for optimal shape. Until the end of the World War II most submarines had additional partial cover on top, bow and stern, built of thinner metal, which was flooded when submerged. Germany went further with Type XXI, the general predecessor of modern submarines, fully enclosing the pressure hull inside the light one, however optimised for submerged navigation unlike earlier designs.
After World War II, approaches split. The Soviet Union changed their designs, basing them on the latest German developments. All post-WWII heavy Soviet and Russian submarines are built with a
double hull structure. American and most other Western submarines retain single-hull approach. They still have light hull sections in bow and stern, which house main ballast tanks and provide hydrodynamically optimized shape, but the main cylindrical hull section has only a single plating layer.
Despite no longer needed for different shape, double-hull approach still has a number of advantages. The ring stiffeners and longitudinals are located between hulls, and the light hull also can be used to mount equipment not requiring constant pressure to operate, while attaching it directly to the pressure hull could cause dangerous local stress. These measures save a lot of space inside the pressure hull, which is much heavier and longer to build than the light hull. In case the submarine is damaged, the light hull can take most of the damage, which does not compromise the boat's integrity, as long as the strong hull is intact. Light hull also can be acoustically decoupled from the pressure hull, significantly reducing noise from internal equipment, improving stealth or allowing to use simpler internal layout and equipment mounting.
The major downside of double-hull structure is the significantly greater amount of manual work required to construct it. The Soviet Union had implemented the welding technology earlier and had enough cheap qualified workforce available, but the high cost of manual labor in the United States made less expensive single-hull approach preferable. Another reason for double-hull construction in the Soviet Union was operation under the
Arctic Ocean, where submarines had to break thick ice to launch the missiles, which could damage the hull. However, double-hull approach is today considered for future submarines in the United States as well, to increase payload capacity, stealth and operational reach .
Pressure hull
The pressure hull is generally constructed of thick high-strength steel with a complex structure and high strength reserve, and is separated with 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, while the missile launch system is located between the main hulls.
The dive depth cannot be increased easily. Simply making the hull thicker increases the weight and requires reduction of the weight of onboard equipment, ultimately resulting in a
bathyscaphe. This is affordable for civilian research submersibles, but not military submarines, so their dive depth was always bound by current technology.
WW1 submarines had their hulls built of
carbon steel, and could not submerge below 100 meters. During World War Two, high-strength alloyed steel was introduced, allowing for depths up to 200 meters. High-strength alloyed steel is still the main material for submarines today, with 250-400 meters depth limit, which cannot be exceeded on a military submarine without sacrificing other characteristics. To exceed that limit, a few submarines were built with
titanium hulls. Titanium is almost as strong as steel, lighter than it, and also is non-magnetic, which is important for stealth. Titanium submarines were especially favored by the Soviets, who developed specialized high-strength alloys, built an industry for producing titanium with affordable costs and have several types of titanium submarines. Titanium alloys allow a major increase in depth, but other systems need to be redesigned as well, so test depth was limited to 1000 meters for
K-278 Komsomolets, the deepest-diving military submarine. An
Alfa class submarine may have successfully operated at 1300 meters , though continuous operation at such depths would be an excessive stress for many submarine systems. Despite its benefits, high costs of titanium construction led to abandonment of titanium submarines idea as the Cold War ended.
The task of building a pressure hull is very difficult, as it must withstand a force of several million tons. 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 is bent, with several points heavily strained. Inevitable minor deviations are resisted by the stiffener rings, but even a one inch deviation from roundness results in over 30 percent decrease of maximal hydrostatic load and consequently dive depth . The hull must therefore be constructed with very high precision. All hull parts must be welded without defects, and all joints are checked several times using different methods. This contributes to very high cost of modern submarines .
Propulsion
Until the advent of nuclear marine propulsion, most 20th century submarines used batteries for running underwater and
gasoline or
diesel engines on the surface and to recharge the batteries. Early boats used gasoline but this quickly gave way to paraffin, then diesel, because of reduced flammability. Diesel-electric became the standard means of propulsion. Initially the diesel or gasoline engine and the electric motor, separated by clutches, were on the same shaft and drove the propeller. This allowed the engine to drive the electric motor as a generator to recharge the batteries and also propel the submarine if required. The clutch between the motor and the engine would be disengaged when the boat dived so that the motor could be used to turn the propeller. The motor could have more than one armature on the shaft — these would be electrically coupled in series for slow speed and parallel for high speed .
In the 1930s the principle was modified for some submarine designs, particularly those of the
U.S. Navy and the British U-class. The engine was no longer attached to the motor/propeller drive shaft but drove a separate generator, which would drive the motors on the surface and/or recharge the batteries. This
diesel-electric propulsion allowed much more flexibility, for example the submarine could travel slowly whilst the engines were running at full power to recharge the batteries as quickly as possible, reducing time on the surface, or use its
snorkel. Also it was now possible to insulate the noisy diesel engines from the pressure hull making the submarine quieter.
There were other power sources attempted—oil-fired steam turbines powered the British
"K" class submarines built during the
First World War and in the following years, but these were not very successful.
This was selected to give them the necessary surface speed to keep up with the British battle fleet.
Steam power was resurrected in the 1950s with the advent of the nuclear-powered steam turbine driving a generator, which is now used in all large submarines. By removing the requirement for atmospheric oxygen these submarines can stay submerged indefinitely so long as food supplies remain . These vessels always have a small battery and diesel engine/generator installation for emergency use if the reactors have to be shut down.
The first mechanically driven submarine was the 1863 French
Plongeur, which used compressed air for propulsion, but anaerobic propulsion was first employed by the Spanish
Ictineo II in 1864. Ictineo's engine used a chemical mix containing a peroxide compound to generate heat for steam propulsion while also providing
oxygen for the crew. The system was not employed again until 1940 when the German Navy tested a system employing the same principles, the Walter
turbine, on the experimental V-80 submarine and later on the naval U-791 submarine.
At the end of the
Second World War the
British and Russians experimented with
hydrogen peroxide/kerosene engines which could be used both above and below the surface. The results were not encouraging enough for this technique to be adopted at the time, and although the Russians deployed a class of submarines with this engine type code named
Quebec by NATO, they were considered a failure. Today several navies, notably
Sweden, now use air-independent propulsion boats which substitute
liquid oxygen for hydrogen peroxide.
The German
Type 212 submarine uses nine 34-kilowatt hydrogen
fuel cells as air-independent propulsion, which makes it first series production submarine using fuel cells.
Small modern commercial submarines usually rely only on batteries if they are never expected to operate independently of a mother ship.
Towards the end of the 20th century some submarines, such as the British Vanguard class, began to be fitted with
pump-jet propulsors instead of propellers. Although these are heavier, more expensive, and often less efficient than a propeller, they are significantly quieter, giving an important tactical advantage.
A possible propulsion system for submarines is the magnetohydrodynamic drive, or "caterpillar drive", which has no moving parts. It was popularized in the movie version of
The Hunt for Red October, written by
Tom Clancy, which portrayed it as a virtually silent system. Although some experimental surface ships have been built with this propulsion system, speeds have not been as high as those hoped. In addition, the noise created by bubbles, and the higher power settings a submarine's reactor would need, mean that it is unlikely to be considered for any military purpose.
Crew
With
nuclear power, submarines can remain submerged for months at a time. Diesel submarines must periodically resurface or
snorkel to recharge their batteries. Most modern military submarines are able to generate
oxygen for their crew by
electrolysis of water. Atmosphere control equipment includes a CO
2 scrubber, which uses a catalyst to remove the gas from air and diffuse it into waste pumped overboard. A machine that uses a catalyst to convert carbon monoxide into carbon dioxide and bonds hydrogen produced from the ship's storage battery with oxygen in the atmosphere to produce water, also found its use. An atmosphere monitoring system samples the air from different areas of the ship for nitrogen, oxygen, hydrogen, R12 and R114 refrigerant, carbon dioxide, carbon monoxide, and others. Poisonous gases are removed, and oxygen is replenished by use of an oxygen bank located in a main ballast tank. Some heavier submarines have two oxygen bleed stations . The oxygen in the air is sometimes kept a few percent less than atmospheric concentration to reduce fire danger.
Fresh water is produced by either an evaporator or a reverse osmosis unit. It is used for showers, sinks, cooking and cleaning. Seawater is used to flush toilets, and the resulting "black water" is stored in a sanitary tank until it is blown overboard using pressurised air or pumped overboard by using a special sanitary pump. The method for blowing sanataries overboard is difficult to operate, and the German
Type VIIC boat U-1206 was lost with casualties because of a mistake with the toilet. Water from showers and sinks is stored separately in "gray water" tanks, which are pumped overboard using the drain pump.
Trash on modern large submarines is usually disposed of using a tube called a Trash Disposal Unit , where it is compacted into a galvanised steel can. At the bottom of the TDU is a large ball valve. An ice plug is set on top of the ball valve to protect it, the cans on top of the ice plug. The top breech door is shut, and the TDU is flooded and equalised with sea pressure, the ball valve is opened and the cans fall out to the ocean floor assisted by scrap iron weights inside the cans.
A typical nuclear submarine has a crew of over 120; non-nuclear boats typically have less than half as many. The conditions on a submarine can be difficult because crewmembers must work in isolation for long periods of time, without contact with their families. Submarines normally maintain
radio silence to avoid detection. Operating a submarine is dangerous, even in peacetime, and many submarines have been lost in accidents.
Women on submarines
In 1995 the
Royal Norwegian Navy became the first navy in the world to appoint a female submarine captain.
In 1998, the
Royal Australian Navy became the second nation to allow women to serve on combat submarines. Canada and Spain followed in permitting women to serve on military submarines. The usual reasons for barring women that are given are: lack of privacy, and "hot bunking" or "hot racking", as due to lack of space this is a common practice on submarines where three sailors share two bunks on a rotating basis. The US Navy, which permits women to serve on almost every other ship in the fleet, only allows three exceptions for women being on board military submarines: Female civilian technicians for a few days at most; Women
midshipmen on an overnight during summer training for both Navy
ROTC and
Naval Academy; Family members for one-day dependent cruises. The US Navy argues it would cost $300,000 per bunk to permit women to serve on submarines versus $4,000 per bunk to allow women to serve on aircraft carriers. However, this calculation is based on the assumption of semi segregation of the female crew, possibly to the extent of structural redesign of the vessel.
Types of military submarines
Military submarines are generally divided into attack submarines, designed to operate against enemy ships, including other submarines, in a hunter-killer role, or strategic ballistic-missile submarines, designed to launch attacks on land-based targets from a position of stealth, also known as "boomers" in the
United States Navy or "bombers" in the
Royal Navy. The division between these classes refers to role rather than construction, and submarines designed to destroy enemy fleets from long distances with multiple nuclear missiles are similar to SSBN in size, armament and other facilities.
Every known strategic, ballistic-missile carrying submarine operated today is nuclear powered. In regard to tactical nuclear weapons, it is widely rumored that
Israel tested nuclear-capable
cruise missiles from two German-built
Dolphin-class diesel submarines in May 2000; if so, these are likely operational today.
U.S. attack submarines no longer carry nuclear-tipped Tomahawk cruise missiles as a result of nuclear arms control agreements. Some older,
Trident class ballistic missile submarines are being converted to carry multiple conventional-warhead, "guided" Tomahawk missiles and thus become redesignated as guided missile submarines. The Russian Federation also possesses several nuclear-powered submarines capable of launching
SS-N-19 anti-ship cruise missiles: the
Kursk was one such submarine. NATO forces designate these craft as SSGN as well.
Attack submarines may be divided in two general types: Nuclear or diesel-electric . Nuclear powered submarines are faster and larger, and have more firepower and longer mission endurance than diesel-electrics. Depending on the submarine's overall mission, the diesel-electric submarine is sometimes more suited for shallow water or
littoral operations. To close the gap between the two very different designs several navies have started the development of air-independent propulsion boats, which are used like diesel-electric submarines with an enlarged diving period.
Various specialized military submarines have also been developed in the past. In World War II, the Japanese used submarines such as its
I-400-class as platforms to launch attack seaplanes. The Germans built their
Type XIV Milchkuh submarines to serve as supply vessels for other submarines.
Midget submarines were used for sabotage and espionage, especially by the Japanese and British navies; for instance five were used by Japan in its attack on
Pearl Harbor. During the early years of the
Cold War, radar-picket submarines such as the USS
Triton were developed to provide radar coverage and direct aircraft operations at long distances ahead of other units.
Ballistic missile submarines
Ballistic missile submarines carry
submarine-launched ballistic missiles with
nuclear warheads, for attacking strategic targets such as cities or
missile silos anywhere in the world. They are currently universally
nuclear-powered, to provide the greatest stealth and endurance. They played an important part in Cold War mutual deterrence, as both the United States and the Soviet Union had the credible ability to conduct a retaliatory strike against the other nation in the event of a first strike. This comprised an important part of the strategy of Mutual Assured Destruction.
The U.S. built 18
Ohio class submarines as
SSBNs, each capable of carrying 24
Trident SLBMs. The first four Ohio class vessels are now being converted to carry Tomahawk guided missiles; the remaining 14 carry Trident II missiles.
For
Russia, see List of NATO reporting names for ballistic missile submarines.
The
Royal Navy possess a single class of four ballistic missile submarines, the
Vanguard class. The Royal Navy's previous ballistic missile submarine class was the
Resolution class, which also consisted of four boats. The
Resolutions, named after battleships to convey the fact they were the new capital ships, were decommissioned when the
Vanguards entered service in the 1990s.
France operates a
force de frappe is the designation of what used to be a triad of air, sea and land based French ...
including a nuclear ballistic submarine fleet made up of one SSBN
Redoutable class and three SSBNs of the
Triomphant class. One additional SSBN of the
Triomphant class is under construction.
The
People's Republic of China's
People's Liberation Army Navy's SLBM inventory is relatively new. China launched its first nuclear-armed submarine in April 1981. The PLAN currently has 1
Xia class at roughly 8,000 tons displacement. The Type 92 is equipped with 12 SLBM launching tubes. China's SLBM program is built around its JL-1 inventory. The Chinese Navy is estimated to have 24 JL-1s. The JL-1 is basically a modified DF-21.
The PLAN plans to replace its JL-1 with an unspecified number of the longer ranged, more modern JL-2s. Deployment on the JL-2 reportedly began in late 2003.
Attack boats
Submarines designed for the purpose of attacking merchant ships or other warships are known as "fast attacks", "hunter-killers", "fast boats", or "fleet submarines" . They typically carry
torpedoes for attacking naval vessels, and today carry cruise missiles for attacking either land-based targets or shipping. On American submarines, cruise missiles can be fired horizontally through a submarine's torpedo tubes, or, on newer vessels, via specially designed
vertical launch tubes. The former has an eff
