Naval warfare is divided into three operational areas: surface warfare, air warfare and underwater warfare. The latter may be subdivided into submarine warfare and anti-submarine warfare as well as mine warfare and mine countermeasures. Each area comprises specialized platforms and strategies used to exploit tactical advantages unique and inherent to that area.
Modern submarine warfare consists primarily of diesel and nuclear submarines using weapons (like torpedoes, missiles or nuclear weapons), as well as advanced sensing equipment, to attack other submarines, shipping or land targets. Submarines may also be used for reconnaissance and landing of special forces as well as deterrence. In some navies they may be used for task force screening. The effectiveness of submarine warfare partly depends on the anti-submarine warfare carried out in response.
Submarine warfare in World War I was partly a fight between German U-Boats and Atlantic supply convoys for Great Britain. British and Allied submarines conducted wide spread operations in the Baltic, North Sea, Atlantic, Mediterranean and Black Seas. Only a few actions occurred outside of the wider European-Atlantic theatre. German submarine attacks on allied merchant ships gave a direct cause for Americans to enter the war in April 1917.
All participants were supposed to abide by the Hague Conventions of 1899 and 1907 but this was found to be impracticable for submarines. Initially German submarines did attempt to comply with the Prize Rules but then went to unrestricted submarine warfare. American diplomatic pressure forced the Germans to stop this for a while but in January 1917 declared a War Zone around the British Isles and sank up to a quarter of shipping entering it, until escorted convoys were introduced.
British submarines were used to lay mines and to attack iron ore shipping in the Baltic. The British submarine flotilla in the Baltic operated in support of the Russians until the Russian-German Pact.
During the war, the British invested effort in developing a submarine that could operate in conjunction with a battleship fleet - the "Fleet Submarine". To achieve the necessary 20 knots (surfaced) the K class submarines were steam powered. In practice the K class were a constant problem and could not operate effectively with a fleet.
Germany was denied submarines by the terms of the Treaty of Versailles and secret production was not legitimized until the Anglo-German Naval Agreement of 1935 under which the UK accepted parity in submarine numbers with the Royal Navy.
In World War II, submarine warfare was split into two main areas - the Atlantic and the Pacific. Although the war still waged in Africa, the Mediterranean Sea was also a very active area for submarine operations. This was particularly true for the British and French as well as the Germans. The Italians were also involved but achieved their greatest success using midget submarines and human torpedoes.
In the Atlantic, where German submarines again acted against Allied convoys, this part of the war was very reminiscent of the latter part of World War I. Many British submarines were active as well, particularly in the Mediterranean and off Norway, against Axis warships, submarines and merchant shipping.
Initially Hitler ordered his submarines to abide by the Prize Rules but this restriction was withdrawn in December 1939. Although mass attacks by submarine had been carried out in the First World War, the "wolf pack" was mainly a tactic of the Second World War U-boats. The main steps in this tactic were as follows:
With the later increase in warship and aircraft escorts the U-boat losses became unacceptable. Many boats were lost, and the earlier "aces" with them.
The advent of the nuclear submarine in the 1950s brought about a major change in submarine warfare. These boats could operate faster, deeper and had much longer endurance. They could be larger and so became missile launching platforms. In response to this the attack submarine became important. The US also used nuclear submarines as radar pickets for a while. Diesel-electric submarines continued to be used as they were better in coastal waters and less expensive. There have also been major advances in sensors and weapons.
Since the Second World War, several wars, such as the Korean War, Indo-Pakistani War of 1971 and the Falklands War, have involved the use of submarines. However, the importance of the submarine has shifted to an even more strategic role than the disruption of merchant shipping, with the advent of the nuclear submarine carrying nuclear weapons to provide second-strike capability. To counter the threat of these submarines, hunter submarines were developed in turn. Later submarine-launched land-attack missiles were employed against Iraq and Afganistan. The role of the submarine has extended with the use of submarine-launched autonomous unmanned vehicles. The development of new air independent propulsion methods has meant that the submarine's need to surface, making it vulnerable, has been reduced.
At the end of his naval warfare book The Price of Admiralty, military historian John Keegan postulates that eventually, almost all roles of surface warships will be taken over by submarines, as they will be the only naval units capable of evading the increasing intelligence capabilities (space satellites, airplanes etc.) that a fight between evenly matched modern states could bring to bear on them.
In wartime a submarine can carry out a number of missions including:
Some theorists such as military historian John Keegan have argued that the extreme vulnerability of surface ships (when facing nations of a similar technological level) to aerial and ship-ship missile attacks will eventually lead to a trend for all types of naval vessels to receive submarine versions.