The first true "Fleet Boat", the P's were the predecessors of the Gato class and all subsequent submarine development through the Tang class (1951). This was the first sub to be made of welded construction (rather then riveted) which allowed for an increase in the pressure hull's test depth and durability. The "P's" were initially commissioned in 1936 and were the first subs to be fitted with air conditioning. With a forward speed of 19 knots they were considered superior to all previous US submarines. Their fire power of six torpedoes, however was regarded by many CO's to be woefully inadequate for their size. Consequently, two external tubes were added to five boats in this class.  Modifications were made throughout the duration of the war as the technology in SONAR, RADAR and weaponry improved. Additional alterations were made to the P's fairwater by removing the plating from the cigarette deck. This was implemented in order to reduce their silhouette and increase diving time. 

An active combatant at the war's outbreak, most boats in this class recorded at least eight war patrols with the USS Permit having conducted fourteen.