Built by the Portsmouth Navy Yard of New Hampshire, the USS Sirago (SS-485), a Tench-class submarine named for a tropical freshwater fish, was launched on 13 May 1945 and commissioned on 13 August 1945. Measuring 311 feet 8 inches long, and displacing more than 1,800 tons surfaced and 2,400 tons submerged, the Sirago was armed with ten 21-inch torpedo tubes. The Sirago conducted her shakedown cruise off the East Coast and in the Caribbean under Commander F. J. Harlfinger II, the boat's first commanding officer.
Upon joining Submarine Squadron 8 (SubRon 8) she transferred to New London, Connecticut, and in January 1946 took part in the destruction of two German submarines near Provincetown, Massachusetts. The Sirago participated in several training operations until December 1948, when she began a GUPPY II conversion at the Philadelphia Naval Shipyard. Upon completion of her conversion in July 1949, she was a modern high-speed attack submarine and joined SubRon 6 in Norfolk, Virginia.