Grayback class submarine was a class of two guided missile carrying submarines of the United States Navy. These submarines carried the short-lived (1955–64) Regulus I and Regulus II nuclear cruise missiles that were quickly phased out by Polaris Submarine Launched Ballistic Missiles (SLBMs). They and the USS Halibut (SSGN-587) were the sole submarines designed specifically to carry Regulus.