United States Porpoise-class submarine

The Porpoise class were submarines built for the United States Navy in the late 1930s, and incorporated a number of modern features that would make them the basis for subsequent Salmon, Sargo, Tambor, Gato, Balao, and Tench classes. Based on the Cachalots, enlarged to incorporate additional main diesels and generators, the Portsmouth boats were all riveted.

In general, they were around 300 ft long and diesel-electric powered. Displacement was 1,934 tons submerged for the first four boats, 1,998 tons for the later ones.

The all-electric drive was troublesome. In this arrangement, the boat's four main diesel engines drove only electric generators, which supplied power to electric motors attached to the propeller shafts. The engines themselves were not connected to the propeller shafts. For submerged propulsion, massive storage batteries supplied electricity to the motors. Problems arose with flashover and arcing in the main motors. There was also a loss of 360 hp in transmission through the electrical system. Their Winton Model 16-201A 16-cylinder diesels also proved problematic, and were eventually replaced with 12-278As.

The Porpoise class consisted of the following subclasses:

P-1 Type
 * (SS-172) USS Porpoise (SS-172)
 * (SS-173) USS Pike (SS-173)

P-3 Type
 * (SS-174) USS Shark (SS-174)
 * (SS-175) USS Tarpon (SS-175)

P-5 Type
 * (SS-176) USS Perch (SS-176)
 * (SS-177) USS Pickerel (SS-177)
 * (SS-178) USS Permit (SS-178)
 * (SS-179) USS Plunger (SS-179)
 * (SS-180) USS Pollack (SS-180)
 * (SS-181) USS Pompano (SS-181)