(SST-1: dp. 303 (surf.), 347 (subm.); 1. 131'3"; b. 13'7"; dr. 12'2" (mean); s. 10 k. (surf.), 10.5 k. (subm.); cpl. 18; a. 1 21" tt.; cl. T-l)
T-l (SST-1)—originally projected as AGSS-570— was laid down on 1 April 1952 at Groton, Conn., by the Electric Boat Division of the General Dynamics Corp.; launched on 17 July 1953; sponsored by Mrs. Charles R. Muir; and placed in service on 9 October 1953, Lt. J. M. Snyder, Jr., in command.
After completing trials off the New England coast, T-l departed New London in February 1954, bound for the Florida coast. Soon after reaching Key West, she began operations with submarine and antisubmarine warfare (ASW) forces in Florida waters. These duties also took her to Guantanamo Bay, Cuba. On 15 May 1956, T-l was named Mackerel; but she retained her hull number, SST-1.
Mackerel participated in fleet exercises off the east coast, mainly conducting training and target assignments including some for the Fleet Sonar School at Key West. She made several cruises testing new equipment for submarines. On 2 April 1957, she departed Key West on a special sound-damping project, en route to Annapolis, Md. After more training and target cruises into the late 1950's, she tested acoustical developments for submarine hulls in waters near the British West Indies in the summer of 1963. She again operated in the West Indies in February 1964, performing similar tasks.
She received new equipment at Groton in the spring of 1966 and headed south, arriving at Key West on 26 June. There, Mackerel conducted experimental work to acquire data to be used in the development of future Navy submarines. After finishing this assignment in March 1967, the submarine had some of her special equipment removed, and she resumed operations at Key West for the Fleet Sonar School.
Mackerel acted as a target for surface and air ASW forces off the Florida coast and in the Caribbean during the late 1960's and into the 1970's. Sometime in 1971, Mackerel was commissioned. She provided target and training services for antisubmarine warfare units of the Atlantic Fleet in the Key West and the Mayport/ Jacksonville operating areas in 1971 and 1972. She made her last dive on 21 July 1972. She remained in reduced-complement status from that day until 31 January 1973 but, nevertheless, conducted junior officer and midshipmen training regularly through October 1972. Mackerel and her sister Marlin (SST-2) were decommissioned on 31 January 1973 in a dual ceremony at the Naval Station, Key West, Fla.; and both were struck from the Navy list on the same day. Mackerel was subsequently scrapped.