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 , , , , , and classes. Based on the s, enlarged to incorporate additional main diesels and generators, the Portsmouth boats were all riveted while the other boats were welded. In some references, the Porpoises are called the "P" class.