Redesignated SS-419 on 3 February 1961, she was recommissioned on 10 March 1962 and underwent overhaul and conversion at the Philadelphia Naval Shipyard before reporting to New London for refresher training on 22 September. On 15 November, she departed New London for four weeks of shakedown out of Puerto Rico, and, on 14 December, she returned to New London to remain there into the new year. From April through August 1963, she operated in the Mediterranean Sea on deployment with the Sixth Fleet. She then returned to New London for local operations and to provide services for the Submarine School. On 1 December 1963, she was redesignated an auxiliary submarine with hull classification symbol AGSS-419. Early in 1964, she was fitted out with an experimental sonar unit. Through the end of 1964, she operated in conjunction with the Naval Underwater Sound Laboratory and the Submarine School, testing and evaluating the new equipment. In 1965, she underwent a major eight-month overhaul and modification at the Philadelphia Naval Shipyard. Her torpedo tubes were removed, two forward compartments thoroughly sound isolated, and a new experimental sonar system, the Brass III, was installed. Operating as a research and development vessel in cooperation with the United States Underwater Sound Laboratory, she began duties which would fill the remaining years of her long career. Assigned primarily to data collection and sonar and acoustic tests in connection with the Brass program, she operated out of New London, conducting underwater systems tests as well as research in sound propagation. In 1968, she visited Britain and port on the Norwegian Sea, spent September through December in antisubmarine warfare exercises; and trained reserves. She continued her research assignments, joining with submarine in the early months of 1972 for a joint American-British oceanographic operation in the eastern Atlantic. She operated occasionally in the Caribbean Sea, taking part in Operation "Springboard" in 1973 and 1974. While moored at the Submarine Base in New London, on 25 October 1974, Tigrone observed the 30th anniversary of her commissioning. Into 1975, she continued research activities off the East Coast, which included a visit to Bermuda in March and operations with air units off Jacksonville and Atlantic City, New Jersey. On 5 May, she began pre-inactivation procedures and, on 27 June 1975, was decommissioned at the Naval Submarine Base, Groton, Connecticut. At the time of her decommissioning, Tigrone was the oldest submarine in commission in the