USS Plunger (SS-179), a Porpoise-class submarine, was the second ship of the United States Navy to be named plunger after a diver or a daring gambler. Unlike most American submarines of the day, she was not named for a fish or other sea-dwelling creature.

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. In some references, the Porpoises are called the "P" class.