USS Seahorse (SS-304), a Balao-class submarine, was the first submarine and second ship of the United States Navy to be named for the seahorse, a small fish whose head and the fore part of its body suggest the head and neck of a horse. Seahorse was laid down on 1 August 1942 by the Mare Island Navy Yard, Vallejo, California. The vessel was launched on 9 January 1943, sponsored by Mrs. Chester C. Smith, and commissioned on 31 March 1943.