US Navy salvage divers raise F-4, the first U.S. submarine sunk in an accident.

USS F-4 (SS-23) was a United States Navy F-class submarine. She originally was named Skate, making her the first ship of the United States Navy named for the skate, but was renamed while under construction. Commissioned in 1913, she operated in the Pacific Ocean until she sank accidentally in 1915, the first commissioned submarine of the U.S. Navy to be lost at sea.

A submarine is a watercraft capable of independent operation underwater. The term "submarine" is also sometimes used historically or informally to refer to remotely operated vehicles and robots, or to medium-sized or smaller vessels. Submarines are referred to as boats rather than ships regardless of their size.