Tambor - class submarine The " Tambor " - class submarine was a United States Navy submarine design , used primarily during World War II . It was the USN ' s first practical fleet submarine and formed the core of the United States Pacific submarine fleet at the time of the US entry into World War II . Design history . Preliminary designs . Early U . S . submarine designs of World War I assigned to escort shipping revealed that they had minimal ability to deter an aggressive threat . Despite the fact that German U - boat s proved beyond a doubt that no navy could be a world sea power without submarines , the role played by U . S . submarines in the defense of the Pacific would have to be rethought , or else flat out discarded , by Navy planners . Following the armistice , and after testing the capabilities of German design , the U . S . Navy began to see the potential for extended offensive submarine operations . Submarine operations with the fleet required boats with both a large cruising radius and a relatively high speed so that they could intercept and stay with their prey . The huge advancement in American technology required to fill that role with " a new all - purpose fleet submarine " also became apparent . After the fiasco of submarine design experienced in the late 1920s , Navy designers finally produced plans for a practical fleet submarine . The lineage of what was to become the fleet submarine actually began with the Porpoise or " P " - class and " Salmon " / " Sargo " or " S " - class submarines , laid down in 1933 and 1935 . These were smaller , more maneuverable boats than some of the varied and earlier V series boats . While these newer P - class and S - class boats were a step in the right direction , they were found to be lacking in speed , reliability and firepower . Tambor class proposal . In the fall of 1937 a proposal for a true fleet submarine ( a submarine intended to operate as part of a larger fleet ) was finally put forward by the team of officers put together by then Commander Charles A . Lockwood ( later admiral and Commander Submarine Fleet Pacific ) , Lt . Cmdr . Andrew I . McKee , planning officer at Portsmouth Navy Yard , and Lt . Armand M . Morgan , head of the Navy ' s submarine design section . It was to be large ( 1 , 500 tons ) , and carry the latest diesel engines , ten torpedo tubes , a gun , and a new Torpedo Data Computer . Habitability would be increased by the addition of fresh water distillation units and air conditioning . However , the design concepts faced opposition from Admiral Thomas Hart , Chairman of the General Board . Hart stubbornly defended the building of small , coastal defense boats ( without " luxuries " like air conditioning ) . Through determination and skilled political maneuvering , the design of Lockwood ' s team prevailed ( though Hart would only consent to a gun ) . This design was finally adopted by the Navy ' s General Board and the Submarine Officers ' Conference for the 1939 program . The plans finally drawn for a practical fleet submarine were those of the " Tambor " or " T " - class submarine . A fairly trim and maneuverable vessel at LOA ( Length Over All ) and 1 , 500 tons ( compared with the LOA and 2 , 000 tons of the varied and experimental but widely disliked predecessor , the V - class ) , the new fleet boats provided sufficient elbow room for long war patrols . The " Gar " class boats were virtually identical to the " T " class and are often listed as " T " class submarines . Design specifications . One key to the success of the " T " class was the development of a compact diesel engine designed in concert with the American railroad industry , which enthusiastically embraced the benefits of diesel - powered locomotives ( and was delighted by the Navy ' s willingness to fund the huge research and development costs associated with their creation ) . Equipped with four of the new diesel engines , the boats could reach top speeds of over and make cruises without suffering from the engine fragility of the compact MAN diesel designs used in some of their predecessors . The " T " Class boats were the last phase of development of US subs prior to the introduction of the " Gato " class in 1942 . These two classes of submarines handled most of the combat duties during the early stages of the war , with the holding the scoring record in the category of " number of ships sunk " by a U . S . submarine . Role . These boats were the core of the 56 boat U . S . Submarine Fleet Pacific when the United States entered World War II in December 1941 . The " T " class design , somewhat refined in the following " Gato " and " Balao " classes , formed the backbone of the wartime US Navy submarine fleet . Ships in class . The last six of the " Tambor " class are often listed as " " Gar " class " submarines