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Submarine: the story on HearLore | HearLore
Submarine
In 1538, a strange experiment took place in the city of Toledo, Spain, before Emperor Charles V and a crowd of nearly ten thousand spectators. Two Greek inventors demonstrated a vessel that could penetrate the bottom of a river while keeping its occupants dry. This early submersible, described in a 1562 report by Joann Taisnier, was a hollow cauldron held in the air by ropes, with seats inside for divers. It was a primitive attempt at underwater navigation, yet it marked the first recorded instance of human-powered submersion. By 1578, English mathematician William Bourne had sketched plans for an underwater vehicle, and in 1596, Scottish theologian John Napier wrote of inventions to sail under water and harm enemies. The first verified submarine capable of independent underwater operation was the Turtle, built in 1775 by American David Bushnell. This acorn-shaped device was hand-powered and used screws for propulsion, designed to accommodate a single person. It was the first military submersible to sink an enemy vessel, the USS Housatonic, in 1864, though the Confederate submarine Hunley also sank during the attack. The Hunley's explosion may have killed its crew instantly, preventing them from pumping the bilge or propelling the submarine. The first submarine to successfully dive, cruise underwater, and resurface under crew control was the Plongeur, launched in 1863 by France. It used compressed air for propulsion, marking the beginning of mechanically powered submarines. The era from 1863 to 1904 saw pivotal developments, including the Whitehead torpedo, designed in 1866 by British engineer Robert Whitehead, which became the first practical self-propelled torpedo. The first submarine commissioned by the United States Navy was the Holland VI, launched on the 17th of May 1897 and purchased on the 11th of April 1900. It used internal combustion engine power on the surface and electric battery power underwater, setting the standard for future designs. The first steam-powered submarines, the Nordenfelt I, were built in 1885, armed with torpedoes and ready for military use. The first submarine to use a diesel engine was the French submarine Aigrette in 1904, which improved the concept by using a diesel rather than a gasoline engine for surface power. Large numbers of these submarines were built, with seventy-six completed before 1914. The Royal Navy commissioned five E-class submarines from Vickers, Barrow-in-Furness, under license from the Holland Torpedo Boat Company from 1901 to 1903. Construction of the boats took longer than anticipated, with the first only ready for a diving trial at sea on the 6th of April 1902. These types of submarines were first used during the Russo-Japanese War of 1904, 05. Due to the blockade at Port Arthur, the Russians sent their submarines to Vladivostok, where by the 1st of January 1905 there were seven boats, enough to create the world's first operational submarine fleet. The new submarine fleet began patrols on the 14th of February, usually lasting for about 24 hours each. The first confrontation with Japanese warships occurred on the 29th of April 1905 when the Russian submarine Som was fired upon by Japanese torpedo boats, but then withdrew.
The first recorded instance of human-powered submersion was demonstrated by two Greek inventors in 1538 before Emperor Charles V in Toledo, Spain. This early vessel was described in a 1562 report by Joann Taisnier as a hollow cauldron held by ropes with seats inside for divers.
When was the first verified submarine built?
The first verified submarine capable of independent underwater operation was the Turtle, built in 1775 by American David Bushnell. This acorn-shaped device was hand-powered and used screws for propulsion to accommodate a single person.
Which submarine sank the first enemy vessel in military history?
The Confederate submarine Hunley became the first military submersible to sink an enemy vessel, the USS Housatonic, in 1864. The Hunley's explosion may have killed its crew instantly, preventing them from pumping the bilge or propelling the submarine.
What was the first submarine to use compressed air for propulsion?
The Plongeur, launched in 1863 by France, was the first submarine to successfully dive, cruise underwater, and resurface under crew control. It used compressed air for propulsion, marking the beginning of mechanically powered submarines.
When did the first submarine reach the deepest point in the ocean?
The bathyscaphe Trieste reached the ocean floor in the Challenger Deep on the 23rd of January 1960, carrying Jacques Piccard and Lieutenant Don Walsh. This was the first time a vessel, crewed or uncrewed, had reached the deepest point in the Earth's oceans.
Which submarine sank the Argentine cruiser ARA General Belgrano?
The British submarine HMS Conqueror sank the Argentine cruiser ARA General Belgrano in 1982 during the Falklands War. This event marked the first sinking by a nuclear-powered submarine in war.
Military submarines first made a significant impact in World War I, with German U-boats playing a central role in the First Battle of the Atlantic. At the outbreak of the war, Germany had only twenty submarines available for combat, including vessels of the diesel-engined U-19 class, which had a sufficient range of 8,900 nautical miles and speed of 13.5 knots to allow them to operate effectively around the entire British coast. By contrast, the Royal Navy had a total of 74 submarines, though of mixed effectiveness. In August 1914, a flotilla of ten U-boats sailed from their base in Heligoland to attack Royal Navy warships in the North Sea in the first submarine war patrol in history. The U-boats' ability to function as practical war machines relied on new tactics, their numbers, and submarine technologies such as the combination diesel-electric power system developed in the preceding years. More submersibles than true submarines, U-boats operated primarily on the surface using regular engines, submerging occasionally to attack under battery power. They were roughly triangular in cross-section, with a distinct keel to control rolling while surfaced, and a distinct bow. During World War I, more than 5,000 Allied ships were sunk by U-boats. The British responded to the German developments in submarine technology with the creation of the K-class submarines. However, these submarines were notoriously dangerous to operate due to their various design flaws and poor maneuverability. During World War II, Germany used submarines to devastating effect in the Battle of the Atlantic, where it attempted to cut Britain's supply routes by sinking more merchant ships than Britain could replace. These merchant ships were vital to supply Britain's population with food, industry with raw material, and armed forces with fuel and armaments. Although the U-boats had been updated in the interwar years, the major innovation was improved communications, encrypted using the Enigma cipher machine. This allowed for mass-attack naval tactics, known as Rudeltaktik or wolfpack, which ultimately ceased to be effective when the U-boat's Enigma was cracked. By the end of the war, almost 3,000 Allied ships, including 175 warships and 2,825 merchantmen, had been sunk by U-boats. Although successful early in the war, Germany's U-boat fleet suffered heavy casualties, losing 793 U-boats and about 28,000 submariners out of 41,000, a casualty rate of about 70 percent. The Imperial Japanese Navy operated the most varied fleet of submarines of any navy, including Kaiten crewed torpedoes, midget submarines, medium-range submarines, purpose-built supply submarines, and long-range fleet submarines. They also had submarines with the highest submerged speeds during World War II and submarines that could carry multiple aircraft. They were also equipped with one of the most advanced torpedoes of the conflict, the oxygen-propelled Type 95. Nevertheless, despite their technical prowess, Japan chose to use its submarines for fleet warfare, and consequently were relatively unsuccessful, as warships were fast, maneuverable, and well-defended compared to merchant ships. The submarine force was the most effective anti-ship weapon in the American arsenal. Submarines, though only about 2 percent of the U.S. Navy, destroyed over 30 percent of the Japanese Navy, including 8 aircraft carriers, 1 battleship, and 11 cruisers. US submarines also destroyed over 60 percent of the Japanese merchant fleet, crippling Japan's ability to supply its military forces and industrial war effort. Allied submarines in the Pacific War destroyed more Japanese shipping than all other weapons combined. This feat was considerably aided by the Imperial Japanese Navy's failure to provide adequate escort forces for the nation's merchant fleet. During World War II, 314 submarines served in the US Navy, of which nearly 260 were deployed to the Pacific. When the Japanese attacked Hawaii in December 1941, 111 boats were in commission; 203 submarines from the Gato, Balao, and Tench classes were commissioned during the war. During the war, 52 US submarines were lost to all causes, with 48 directly due to hostilities. The others were lost to accidents or, in the case of USS S-33, friendly fire. US submarines sank 1,560 enemy vessels, a total tonnage of 5.3 million tons, representing 55 percent of the total sunk. The Royal Navy Submarine Service was used primarily in the classic Axis blockade. Its major operating areas were around Norway, in the Mediterranean against the Axis supply routes to North Africa, and in the Far East. In that war, British submarines sank 2 million tons of enemy shipping and 57 major warships, the latter including 35 submarines. Among these is the only documented instance of a submarine sinking another submarine while both were submerged. This occurred when HMS Venturer engaged U-482; the Venturer crew manually computed a successful firing solution against a three-dimensionally maneuvering target using techniques which became the basis of modern torpedo computer targeting systems. Seventy-four British submarines were lost, the majority, forty-two, in the Mediterranean.
The Nuclear Age
The first launch of a cruise missile from a submarine occurred in July 1953, from the deck of USS Tunny, a World War II fleet boat modified to carry the missile with a nuclear warhead. Tunny and its sister boat, USS Grayback, were the United States' first nuclear deterrent patrol submarines. In the 1950s, nuclear power partially replaced diesel-electric propulsion. Equipment was also developed to extract oxygen from sea water. These two innovations gave submarines the ability to remain submerged for weeks or months. Most of the naval submarines built since that time in the US, the Soviet Union, the UK, and France have been powered by a nuclear reactor. In 1959, 1960, the first ballistic missile submarines were put into service by both the United States and the Soviet Union as part of the Cold War nuclear deterrent strategy. During the Cold War, the US and the Soviet Union maintained large submarine fleets that engaged in cat-and-mouse games. The Soviet Union lost at least four submarines during this period: K-8 was lost in 1968, a part of which the CIA retrieved from the ocean floor with the Howard Hughes-designed ship Glomar Explorer; K-129 was lost in 1970; K-219 was lost in 1986; and K-278 Komsomolets was lost in 1989, which held a depth record among military submarines. Many other Soviet subs, such as K-27, the first Soviet nuclear submarine, and the first Soviet sub to reach the North Pole, were badly damaged by fire or radiation leaks. The US lost two nuclear submarines during this time: USS Thresher due to equipment failure during a test dive while at its operational limit, and USS Scorpion due to unknown causes. During the Indo-Pakistani War of 1971, the Pakistan Navy's PNS Hangor sank the Indian frigate INS Khukri. This was the first sinking by a submarine since World War II. During the same war, PNS Ghazi, a Tench-class submarine on loan to Pakistan from the US, was sunk by the Indian Navy. It was the first submarine combat loss since World War II. In 1982 during the Falklands War, the Argentine cruiser ARA General Belgrano was sunk by the British submarine HMS Conqueror, the first sinking by a nuclear-powered submarine in war. Some weeks later, on the 16th of June, during the Lebanon War, an unnamed Israeli submarine torpedoed and sank the Lebanese coaster Transit, which was carrying 56 Palestinian refugees to Cyprus, in the belief that the vessel was evacuating anti-Israeli militias. The ship was hit by two torpedoes, managed to run aground but eventually sank. There were 25 dead, including her captain. The Israeli Navy disclosed the incident in November 2018. 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 World War II 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 sank the Argentine cruiser. 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. An Argentine submarine remained at sea, however.
The Deep Dive
In 1960, Jacques Piccard and Don Walsh were the first people to explore the deepest part of the world's ocean, and the deepest location on the surface of the Earth's crust, in the bathyscaphe Trieste, designed by Auguste Piccard. On the 5th of 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 the 23rd of January 1960, Trieste reached the ocean floor in the Challenger Deep, the deepest southern part of the Mariana Trench, carrying Jacques Piccard and Lieutenant Don Walsh, USN. 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 10,916 meters, although this was later revised to 10,911 meters, and more accurate measurements made in 1995 have found the Challenger Deep slightly shallower, at 10,935 meters. 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 instability is the usual failure mode. Inevitable minor deviations are resisted by 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 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 attack submarine costs US$2.6 billion, over US$200,000 per ton of displacement. WWI submarines had hulls of carbon steel, with a maximum depth of 100 meters. During WWII, high-strength alloyed steel was introduced, allowing depths of 200 meters. High-strength alloy steel remains the primary material for submarines today, with depths of 300 meters, 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 meters for the K-278 Komsomolets, the deepest-diving combat submarine. An Albatros-class submarine may have successfully operated at 1,250 meters, 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 to date is Trieste. On the 5th of 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 the 23rd of January 1960, Trieste reached the ocean floor in the Challenger Deep, the deepest southern part of the Mariana Trench, carrying Jacques Piccard and Lieutenant Don Walsh, USN. 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 10,916 meters, although this was later revised to 10,911 meters, and more accurate measurements made in 1995 have found the Challenger Deep slightly shallower, at 10,935 meters.
The Silent Revolution
The first submarines were propelled by humans. The first mechanically driven submarine was the 1863 French Plongeur, which used compressed air for propulsion. Anaerobic propulsion was first employed by the Spanish Ictineo II in 1864, which used a solution of zinc, manganese dioxide, and potassium chlorate to generate sufficient heat to power a steam engine, while also providing oxygen for the crew. A similar system was not employed again until 1940 when the German Navy tested a hydrogen peroxide-based system, the Walter turbine, on the experimental V-80 submarine and later on the naval and Type XVII submarines; the system was further developed for the British XE-class, completed in 1958. Until the advent of nuclear marine propulsion, most 20th-century submarines used electric motors and batteries for running underwater and combustion engines on the surface, and for battery recharging. Early submarines used gasoline engines but this quickly gave way to kerosene and then diesel engines because of reduced flammability and, with diesel, improved fuel-efficiency and thus also greater range. A combination of diesel and electric propulsion became the norm. Initially, the combustion engine and the electric motor were in most cases connected to the same shaft so that both could directly drive the propeller. The combustion engine was placed at the front end of the stern section with the electric motor behind it followed by the propeller shaft. The engine was connected to the motor by a clutch and the motor in turn connected to the propeller shaft by another clutch. With only the rear clutch engaged, the electric motor could drive the propeller, as required for fully submerged operation. With both clutches engaged, the combustion engine could drive the propeller, as was possible when operating on the surface or, at a later stage, when snorkeling. The electric motor would in this case serve as a generator to charge the batteries or, if no charging was needed, be allowed to rotate freely. With only the front clutch engaged, the combustion engine could drive the electric motor as a generator for charging the batteries without simultaneously forcing the propeller to move. The motor could have multiple armatures on the shaft, which could be electrically coupled in series for slow speed and in parallel for high speed, these connections were called group down and group up, respectively. While most early submarines used a direct mechanical connection between the combustion engine and the propeller, an alternative solution was considered as well as implemented at a very early stage. That solution consists in first converting the work of the combustion engine into electric energy via a dedicated generator. This energy is then used to drive the propeller via the electric motor and, to the extent required, for charging the batteries. In this configuration, the electric motor is thus responsible for driving the propeller at all times, regardless of whether air is available so that the combustion engine can also be used or not. Among the pioneers of this alternative solution was the very first submarine of the Swedish Navy, HMS Hajen, later renamed Ub no 1, launched in 1904. While its design was generally inspired by the first submarine commissioned by the US Navy, USS Holland, it deviated from the latter in at least three significant ways: by adding a periscope, by replacing the gasoline engine by a semidiesel engine, a hot-bulb engine primarily meant to be fueled by kerosene, later replaced by a true diesel engine, and by severing the mechanical link between the combustion engine and the propeller by instead letting the former drive a dedicated generator. By so doing, it took three significant steps toward what was eventually to become the dominant technology for conventional, that is, non-nuclear, submarines. In the following years, the Swedish Navy added another seven submarines in three different classes, Undervattensbåten No 2, Laxen, and Abborren class, using the same propulsion technology but fitted with true diesel engines rather than semidiesels from the outset. Since by that time, the technology was usually based on the diesel engine rather than some other type of combustion engine, it eventually came to be known as diesel-electric transmission. Like many other early submarines, those initially designed in Sweden were quite small, less than 200 tonnes, and thus confined to littoral operation. When the Swedish Navy wanted to add larger vessels, capable of operating further from the shore, their designs were purchased from companies abroad that already had the required experience: first Italian Fiat-Laurenti and later German A.G. Weser and IvS. As a side-effect, the diesel-electric transmission was temporarily abandoned. However, diesel-electric transmission was immediately reintroduced when Sweden began designing its own submarines again in the mid-1930s. From that point onwards, it has been consistently used for all new classes of Swedish submarines, albeit supplemented by air-independent propulsion, AIP, as provided by Stirling engines beginning with HMS Näcken in 1988. Another early adopter of diesel-electric transmission was the US Navy, whose Bureau of Engineering proposed its use in 1928. It was subsequently tried in the S-class submarines, S-1, S-2, and S-3, before being put into production with the Porpoise class of the 1930s. From that point onwards, it continued to be used on most US conventional submarines. Apart from the British U-class and some submarines of the Imperial Japanese Navy that used separate diesel generators for low speed running, few navies other than those of Sweden and the US made much use of diesel-electric transmission before 1945. After World War II, by contrast, it gradually became the dominant mode of propulsion for conventional submarines. However, its adoption was not always swift. Notably, the Soviet Navy did not introduce diesel-electric transmission on its conventional submarines until 1980 with its Paltus class. If diesel-electric transmission had only brought advantages and no disadvantages in comparison with a system that mechanically connects the diesel engine to the propeller, it would undoubtedly have become dominant much earlier. The disadvantages include the following: It entails a loss of fuel-efficiency as well as power by converting the output of the diesel engine into electricity. While both generators and electric motors are known to be very efficient, their efficiency nevertheless falls short of 100 percent. It requires an additional component in the form of a dedicated generator. Since the electric motor is always used to drive the propeller it can no longer step in to take on generator service as well. It does not allow the diesel engine and the electrical motor to join forces by simultaneously driving the propeller mechanically for maximum speed when the submarine is surfaced or snorkeling. This may, however, be of little practical importance inasmuch as the option it prevents is one that would leave the submarine at a risk of having to dive with its batteries at least partly depleted. The reason why diesel-electric transmission has become the dominant alternative in spite of these disadvantages is of course that it also comes with many advantages and that, on balance, these have eventually been found to be more important. The advantages include the following: It reduces external noise by severing the direct and rigid mechanical link between the relatively noisy diesel engine on the one hand and the propeller shaft and hull on the other. With stealth being of paramount importance to submarines, this is a very significant advantage. It increases the readiness to dive, which is of course vital for a submarine. The only thing required from a propulsion point of view is to shut down the diesel. It makes the speed of the diesel engine temporarily independent of the speed of the submarine. This in turn often makes it possible to run the diesel at close to optimal speed from a fuel-efficiency as well as durability point of view. It also makes it possible to reduce the time spent surfaced or snorkeling by running the diesel at maximum speed without affecting the speed of the submarine itself. It eliminates the clutches otherwise required to connect the diesel engine, the electric motor, and the propeller shaft. This in turn saves space, increases reliability and reduces maintenance costs. It increases flexibility with regard to how the driveline components are configured, positioned, and maintained. For example, the diesel no longer has to be aligned with the electric motor and propeller shaft, two diesels can be used to power a single propeller, or vice versa, and one diesel can be turned off for maintenance as long as a second is available to provide the required amount of electricity. It facilitates the integration of additional primary sources of energy, beside the diesel engine, such as various kinds of air-independent power systems. With one or more electric motors always driving the propeller, such systems can easily be introduced as yet another source of electric energy in addition to the diesel engine and the batteries.
The Snorkel and The X-Stern
During World War II the Germans experimented with the idea of the schnorchel, or snorkel, from captured Dutch submarines but did not see the need for them until rather late in the war. The schnorchel is a retractable pipe that supplies air to the diesel engines while submerged at periscope depth, allowing the boat to cruise and recharge its batteries while maintaining a degree of stealth. Especially as first implemented however, it turned out to be far from a perfect solution. There were problems with the device's valve sticking shut or closing as it dunked in rough weather. Since the system used the entire pressure hull as a buffer, the diesels would instantaneously suck huge volumes of air from the boat's compartments, and the crew often suffered painful ear injuries. Speed was limited to 8 knots, lest the device snap from stress. The schnorchel also created noise that made the boat easier to detect with sonar, yet more difficult for the on-board sonar to detect signals from other vessels. Finally, allied radar eventually became sufficiently advanced that the schnorchel mast could be detected beyond visual range. In clear weather, diesel exhausts can be seen on the surface to a distance of about three miles, while periscope feather, the wave created by the snorkel or periscope moving through the water, is visible from far off in calm sea conditions. Modern radar is also capable of detecting a snorkel in calm sea conditions. The problem of the diesels causing a vacuum in the submarine when the head valve is submerged still exists in later model diesel submarines but is mitigated by high-vacuum cut-off sensors that shut down the engines when the vacuum in the ship reaches a pre-set point. Modern snorkel induction masts have a fail-safe design using compressed air, controlled by a simple electrical circuit, to hold the head valve open against the pull of a powerful spring. Seawater washing over the mast shorts out exposed electrodes on top, breaking the control, and shutting the head valve while it is submerged. US submarines did not adopt the use of snorkels until after World War II. Air-independent propulsion was first employed by the Spanish Ictineo II in 1864, which used a solution of zinc, manganese dioxide, and potassium chlorate to generate sufficient heat to power a steam engine, while also providing oxygen for the crew. A similar system was not employed again until 1940 when the German Navy tested a hydrogen peroxide-based system, the Walter turbine, on the experimental V-80 submarine and later on the naval and Type XVII submarines; the system was further developed for the British XE-class, completed in 1958. Today several navies use air-independent propulsion. Notably Sweden uses Stirling technology on the Näcken and Sjöormen classes. The Stirling engine is heated by burning diesel fuel with liquid oxygen from cryogenic tanks. A newer development in air-independent propulsion is hydrogen fuel cells, first used on the German Type 212 submarine, with nine 34 kW or two 120 kW cells. Fuel cells are also used in the new Spanish S-80 class, although with the fuel stored as ethanol and then converted into hydrogen before use. One new technology that is being introduced starting with the Japanese Navy's eleventh Sōryū-class submarine, JS Oryū, is a more modern battery, the lithium-ion battery. These batteries have about double the electric storage of traditional batteries, and by changing out the lead-acid batteries in their normal storage areas plus filling up the large hull space normally devoted to AIP engine and fuel tanks with many tons of lithium-ion batteries, modern submarines can actually return to a pure diesel-electric configuration yet have the added underwater range and power normally associated with AIP equipped submarines. 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-form 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. 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, together with propelling the boat upwards. Such surfacing is very quick, so the vessel may even partially jump out of the water, potentially damaging submarine systems.
The Modern Submarine
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 knots, 18 kilometers per hour, 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 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 Trieste 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, 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 Russian K-278 Komsomolets, 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 maximum depth of 100 meters. During WWII, high-strength alloyed steel was introduced, allowing depths of 200 meters. High-strength alloy steel remains the primary material for submarines today, with depths of 300 meters, 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 meters for the K-278 Komsomolets, the deepest-diving combat submarine. An Albatros-class submarine may have successfully operated at 1,250 meters, 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 to date is Trieste. On the 5th of 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 the 23rd of January 1960, Trieste reached the ocean floor in the Challenger Deep, the deepest southern part of the Mariana Trench, carrying Jacques Piccard and Lieutenant Don Walsh, USN. 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 10,916 meters, although this was later revised to 10,911 meters, and more accurate measurements made in 1995 have found the Challenger Deep slightly shallower, at 10,935 meters. 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 instability is the usual failure mode. Inevitable minor deviations are resisted by 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 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 attack submarine costs US$2.6 billion, over US$200,000 per ton of displacement. Steam power was resurrected in the 1950s with a nuclear-powered steam turbine driving a generator. By eliminating the need for atmospheric oxygen, the time that a submarine could remain submerged was limited only by its food stores, as breathing air was recycled and fresh water distilled from seawater. More importantly, a nuclear submarine has unlimited range at top speed. This allows it to travel from its operating base to the combat zone in a much shorter time and makes it a far more difficult target for most anti-submarine weapons. Nuclear-powered submarines have a relatively small battery and diesel engine/generator powerplant for emergency use if the reactors must be shut down. Nuclear power is now used in all large submarines, but due to the high cost and large size of nuclear reactors, smaller submarines still use diesel-electric propulsion. The ratio of larger to smaller submarines depends on strategic needs. The US Navy, French Navy, and the British Royal Navy operate only nuclear submarines, which is explained by the need for distant operations. Other major operators rely on a mix of nuclear submarines for strategic purposes and diesel-electric submarines for defense. Most fleets have no nuclear submarines, due to the limited availability of nuclear power and submarine technology. Diesel-electric submarines have a stealth advantage over their nuclear counterparts. Nuclear submarines generate noise from coolant pumps and turbo-machinery needed to operate the reactor, even at low power levels. Some nuclear submarines such as the American Los Angeles-class can operate with their reactor coolant pumps secured, making them quieter than electric subs. A conventional submarine operating on batteries is almost completely silent, the only noise coming from the shaft bearings, propeller, and flow noise around the hull, all of which stops when the sub hovers in mid-water to listen, leaving only the noise from crew activity. Commercial submarines usually rely only on batteries, since they operate in conjunction with a mother ship. Several serious nuclear and radiation accidents have involved nuclear submarine mishaps. The reactor accident in 1961 resulted in 8 deaths and more than 30 other people were over-exposed to radiation. The reactor accident in 1968 resulted in 9 fatalities and 83 other injuries. The accident in 1985 resulted in 10 fatalities and 49 other.