Attack submarine An attack submarine or hunter - killer submarine is a submarine specifically designed for the purpose of attacking and sinking other submarines , surface combatant s and merchant vessels . In the Soviet and Russian navies they were and are called " multi - purpose submarines " . They are also used to protect friendly surface combatants and missile submarines . Some attack subs are also armed with cruise missile s mounted in vertical launch tubes , increasing the scope of their potential missions to include land targets . Attack submarines may be either nuclear - powered or diesel - electric ( " conventionally " ) powered . In the United States Navy naming system , and in the equivalent NATO system ( STANAG 1166 ) , nuclear - powered attack submarines are known as SSNs and their diesel - electric predecessors were SSKs . In the US Navy , SSNs are unofficially called " fast attacks " . History . Origins . In the action of 9 February 1945 , HMS " Venturer " sank " U - 864 " while both were at periscope depth . This was the first and so far only intentional sinking of a submerged submarine by a submerged submarine . " U - 864 " was snorkeling , thus producing much noise for " Venturer " s hydrophone s ( an early form of passive sonar ) to detect , and " Venturer " was fortunate in having over 45 minutes to plot the U - boat ' s zig - zag course by observing the snorkel mast . " Venturer " ' s commander , James S . " Jimmy " Launders , was astute in assuming the U - boat would execute an " emergency deep " maneuver once it heard the torpedoes in the water , thus the " spread " of four torpedoes immediately available was aimed on that assumption . One hit , sinking the U - boat . Following World War II , advanced German submarines , especially the Type XXI U - boat , became available to the Allies , particularly the United States Navy and the Soviet Navy . Initially , the Type XVII U - boat , with a Walter hydrogen peroxide - fueled gas turbine allowing high sustained underwater speed , was thought to be more developed than was actually the case , and was viewed as the submarine technology of the immediate future . However , the Type XXI , streamlined and with a high battery capacity for high submerged speed , was fully developed and became the basis for most non - nuclear submarine designs worldwide through the 1950s . In the US Navy , the Greater Underwater Propulsion Power Program ( GUPPY ) was developed to modernize World War II submarines along the lines of the Type XXI . It was realized that the Soviet Union had acquired Type XXI and other advanced U - boats and would soon be putting their own equivalents into production . In 1948 the US Navy prepared estimates of the number of anti - submarine warfare ( ASW ) - capable submarines that would be needed to counter the hundreds of advanced Soviet submarines that were expected to be in service by 1960 . Two scenarios were considered : a reasonable scenario assuming the Soviets would build to their existing force level of about 360 submarines , and a " nightmare " scenario projecting that the Soviets could build submarines as fast as the Germans had built U - boats , with a force level of 2 , 000 submarines . The projected US SSK force levels for these scenarios were 250 for the former and 970 for the latter . Additional anti - surface , guided missile , and radar picket submarines would also be needed . By comparison , the total US submarine force at the end of World War II , excluding obsolescent training submarines , was just over 200 boats . A small submarine suitable for mass production was designed to meet the SSK requirement . This resulted in the three submarines of the " K - 1 " class ( later named the " Barracuda " class ) , which entered service in 1951 . At surfaced , they were considerably smaller than the boats produced in World War II . They were equipped with an advanced passive sonar , the bow - mounted BQR - 4 , but had only four torpedo tube s . Initially , a sonar located around the conning tower was considered , but tests showed that bow - mounted sonar was much less affected by the submarine ' s own noise . While developing the purpose - built SSKs , consideration was given to converting World War II submarines into SSKs . The less - capable " Gato " class was chosen for this , as the deeper - diving " Balao " - and " Tench " - class boats were being upgraded as GUPPYs . Seven " Gato " - class boats were converted to SSKs in 1951 - 53 . These had the bow - mounted BQR - 4 sonar of the other SSKs , with four of the six bow torpedo tubes removed to make room for the sonar and its electronics . The four stern torpedo tubes were retained . Two diesel engines were removed , and the auxiliary machinery was relocated in their place and sound - isolated to reduce the submarine ' s own noise . The Soviets took longer than anticipated to start producing new submarines in quantity . By 1952 only ten had entered service . However , production was soon ramped up . By the end of 1960 a total of 320 new Soviet submarines had been built ( very close to the USN ' s 1948 low - end assumption ) , 215 of them the Project 613 class ( NATO Whiskey class ) , a smaller derivative of the Type XXI . Significantly , eight of the new submarines were nuclear - powered . The nuclear era begins . , the world ' s first nuclear submarine , was operational in 1955 ; the Soviets followed this only three years later with their first Project 627 " Kit " - class SSN ( NATO November class ) . Since a nuclear submarine could maintain a high speed at a deep depth indefinitely , conventional SSKs would be useless against them except in shallow water . As the development and deployment of nuclear submarines proceeded , in 1957 - 59 the US Navy ' s SSKs were redesignated and decommissioned or reassigned to other duties . It had become apparent that all nuclear submarines would have to perform ASW missions . Research proceeded rapidly to maximize the potential of the nuclear submarine for this and other missions . The US Navy developed a fully streamlined hull form and tested other technologies with the conventional , commissioned in 1953 . The new hull form was first operationalized with the five " Skipjack " class boats , which entered service beginning in 1959 . The lead ship of the class was declared the " world ' s fastest submarine " following trials in 1958 , although the actual speed was kept secret . Sonar research showed that a sonar sphere capable of three - dimensional operation , mounted at the very bow of a streamlined submarine , would increase detection performance . This was recommended by Project Nobska , a 1956 study ordered by Chief of Naval Operations Admiral Arleigh Burke . The " Thresher " class and the one - off were the first with a bow - mounted sonar sphere in 1961 ; midships torpedo tubes angled outboard were fitted to make room for the sphere . " Tullibee " was a kind of nuclear - powered SSK ; she was slow but ultra - quiet with turbo - electric drive . Her slow speed was a liability and the type was not repeated , as " Thresher " was faster with twice as many torpedoes , included comparable sound silencing improvements , and was commissioned only nine months later . incorporated numerous advances on previous classes including an increased diving depth ; her loss in April 1963 triggered a major redesign of subsequent US submarines known as the SUBSAFE program . However , " Thresher " ' s general arrangement and concept were continued in all subsequent US Navy attack submarines . The first fully streamlined Soviet submarines were the Project 667A " Navaga " class ( NATO Yankee class ) , Project 670 " Skat " class ( NATO Charlie I class ) , and Project 671 " Yorsh " class ( NATO Victor I class ) , all of which first entered service in 1967 .