During the late summer and early fall of 1968, "Tench" took part in a NATO exercise, Operation "Silvertower," in the eastern Atlantic. During that assignment, she visited ports in the United Kingdom, Germany, and Portugal. The submarine returned to New London on 4 November and began her final 19 months of active service. Near the end of her career, she was given hull classification symbol AGSS-417 (general auxiliary submarine) on 1 October 1969. She was placed in commission, in reserve, at Philadelphia, Pennsylvania, later that month; and, on 8 May 1970, "Tench" was placed out of commission. Berthed at Philadelphia, "Tench" remained in reserve until 1973. On 16 August 1973, her name was stricken from the Naval Vessel Register, and she was subsequently scrapped.