USS Mackerel ( SST - 1 ) USS " Mackerel " ( SST - 1 ) , originally known as USS " T - 1 " ( SST - 1 ) , was the lead ship of the " T - 1 " - class of training submarine s . She was the second submarine of the United States Navy named for the mackerel , a common food and sport fish , and was in service from 1953 to 1973 . She was one of the smallest operational submarines ever built for the U . S . Navy . Construction and commissioning . " T - 1 " was originally planned as an experimental auxiliary submarine with hull number AGSS - 570 , but she was redesignated as a training submarine ( SST - 1 ) and her hull number was changed to SST - 1 . She was laid down on 1 April 1952 , at the Electric Boat Division of General Dynamics Corporation at Groton , Connecticut . She was launched on 17 July 1953 , sponsored by Mrs . Charles R . Muir , and placed in non - commissioned service as USS " T - 1 " on 9 October 1953 , with Lieutenant J . M . Snyder , Jr . , in command . Service history . Training , target , and equipment testing services , 1954 – 1966 . After completing sea trials in the New London , and Massachusetts Bay areas , " T - 1 " departed in February 1954 for Key West , Florida . Arriving at Key West , she commenced operations with submarine and antisubmarine forces in the areas of southern Florida and Guantanamo Bay , Cuba , providing services to the Fleet Training Group working up recently constructed and recently overhauled antisubmarine warships . On 15 July 1956 , " T - 1 " was renamed " Mackerel " , but retained her hull number , SST - 1 . Following her renaming , " Mackerel " participated in fleet exercises off the United States East Coast , mainly conducting training assignments and providing services as a target , including some for the Fleet Sonar School at Key West . She also made several cruises testing new equipment for submarines . On 2 April 1957 , she departed Key West on a special sound - damping project during a voyage to Annapolis , Maryland . She conducted more training and target cruises into the early 1960s . In 1963 , " Mackerel " conducted the first of her test and evaluation voyages . Departing Key West on 8 July 1963 , she sailed to the British West Indies where she tested acoustical developments in submarine hulls for a two ‑ week period in waters near the British West Indies . In addition to resumption of her routine duties , she again operated in the West Indies in February 1964 , again performing tasks related to evaluating submarine - hull acoustic developments . From 7 March 1965 to 4 April 1965 , " Mackerel " joined her sister ship and attack submarine s , , and , along with a task force under Commander , Mine Force , in participating in mine warfare maneuvers . Testing equipment for " NR - 1 " , 1966 - 1967 . During May and June 1966 , Electric Boat installed special equipment in " Mackerel " at Groton . " Mackerel " then transited south to Key West , arriving there on 26 June 1966 . At Key West , she conducted experimental work during the rest of 1966 and in early 1967 to acquire data to be used in the development of future U . S . Navy submarines . She evaluated equipment intended for the NR - 1 Deep Submergence Craft , including keel - mounted wheels for rolling over the ocean floor , thrusters , external television cameras , a manipulator arm , and experimental sonar . " Mackerel " " bottomed " — deliberately settled on the sea floor — some 225 times during the nine - month evaluation period . She completed this assignment during March 1967 , after which she had some of her special equipment removed . At the same time she undertook the additional task of providing shiphandling training for submarine force junior officers . During June and July 1967 , while " Mackerel " in drydock at Key West , additional special project equipment was removed from her . Target services , 1967 - 1973 . " Mackerel " resumed operations at Key West in 1967 , running submerged to serve as a target for vessels used to train sonar operators at the Fleet Sonar School ; at the same time , she undertook the additional task of providing shiphandling training for submarine force junior officers . She also acted as a target for surface and air antisubmarine warfare forces practicing off the Florida coast and in the Caribbean during the late 1960s and early 1970s . In 1971 and 1972 , she provided target and training services for antisubmarine warfare units of the United States Atlantic Fleet in the Key West and the Mayport / Jacksonville , Florida , operating areas . Apparently , her non - commissioned service period ended when she was finally commissioned sometime in 1971 . " Mackerel " made her last dive on 21 July 1972 . After that , she remained in service with a reduced crew and conducted junior officer and midshipman training on the surface regularly through October 1972 . She was taken out of service on 3 January 1973 . Decommissioning and disposal . " Mackerel " and her sister were decommissioned on 31 January 1973 in a dual ceremony at Naval Station Key West . Both also were struck from the Naval Vessel Register that day . " Mackerel " was sunk as a target off Puerto Rico on 18 October 1978 .