"Grayback" represented a new class of SSG guided missile submarines, and was to be the first to carry the Regulus II sea-to-surface missile. In 1958, "Grayback" conducted tests and shakedown along the West Coast. While operating out of Naval Base Ventura County in Port Hueneme, California, in September 1958 she conducted the first successful launching of a Regulus II missile from a submarine, whose predecessor, Regulus I, had led to the capability of navies to attack land bases since its deployment in 1957. Regulus II was cancelled in December 1958 except for test firing of missiles already built, so "Grayback" operationally deployed with four Regulus I missiles. Departing San Diego, California, on 30 October, "Grayback" arrived at Pearl Harbor on 8 November for a month of exercises and maneuvers before returning to Mare Island for her "10,000 mile checkup."