Amphion - class submarine The Amphion " class ( also known as the " A " class and Acheron " class ) of diesel - electric submarine s were ordered by the British Admiralty in 1943 , upon the realisation that the new Pacific theatre of war following the attack on Pearl Harbor needed a new type of submarine . They were originally designed to replace the S - class and T - class submarines , which were too slow and unable to dive deep enough to be suited to Pacific waters during World War II . They were an enlargement of the T class , arranged for fast , simple construction and to utilize much of the materials and equipment set aside for the T boats . They had a high , flared bow for excellent sea performance and had effective air conditioning , essential for Far East submarine operations . They were operated by a crew of between 60 and 68 . Originally , 46 submarines were ordered , but only 18 were launched ( 10 by Vickers - Armstrong in Barrow - in - Furness ) and 16 commissioned , the other 2 hulls being used for crush testing . The class was designed for quick construction , using an entirely welded hull which could be fabricated in sections , a technique new to Britain but standard for German U - boat s . Each submarine took about 8 months from keel - laying to launching , compared with around 15 months for the earlier T class , but only two of the boats were completed before the end of the war : " Amphion " , launched in August 1944 , and " Astute " in January 1945 ; neither saw action . The " Amphion " class was one of only two new British submarine designs produced during World War II , the other being the X - craft 4 - man submarines . Wartime experience had shown that submarines had to operate further from the United Kingdom and with larger patrol areas than had been foreseen — in the Far East and Mediterranean for example — so the faster and slightly larger A class was designed to have a longer range than the T class , and accommodation suitable for longer missions . After World War II various modifications were made to these Overseas Patrol Submarines , as they were known . A snort mast based on the " schnorkel " used by U - boat s during the war , a radar which could be used from periscope depth , and a night periscope were added to the A - and surviving T - class submarines . In response to the start of the cold war in the early 1950s their target changed from surface ships to Soviet submarines . In January 1948 the primary operational function of the British submarine fleet was announced to be interception of Soviet submarines slipping out of their bases in Northern Russia , potentially to attack British and Allied merchant vessels . The following April Assistant Chief of Naval Staff Rear - Admiral Geoffrey Oliver circulated a paper in which he proposed that British submarines take a more offensive role , attacking Soviet submarines off the Northern Russian coast and mining the waters in the area . With the dramatically reduced surface fleet , he commented that this was one of the few methods the Royal Navy had for " getting to the enemy on his home ground " . The A - and T - classes were refitted for their new role between 1955 and 1960 with a complete rebuild of the forward and after hull section , lengthening and streamlining of the upper decks and conning towers , removal of deck guns to improve underwater speed and noise , removal of external torpedo tubes , and greatly improved sonar . When " Affray " was lost in 1951 all the " Amphion " class were briefly confined to port pending investigation into her loss . The " Amphion " class served the Royal Navy for almost three decades as the backbone of the Royal Naval Submarine Service , and was gradually replaced with the " Porpoise " and " Oberon " patrol classes that began to be phased in 1958 . The last operational " Amphion " - class boat , " Andrew " , was decommissioned in 1974 . Boats . Built at HM Dockyard , Plymouth . These were the two vessels which were launched but not completed . Cancelled orders . In 1945 , besides the two vessels at Devonport , the following twenty - seven orders were cancelled :