On 2 June 1945 she started her second war patrol, and on 10 July 1945 fired torpedoes at a surfaced Japanese submarine I-162, after which Lionfish's crew heard explosions and observed smoke through their periscope, although I-162 was undamaged.

Lionfish ended her second and last war patrol performing lifeguard duty (the rescue of downed fliers) off the coast of Japan.

Lionfish was recommissioned on 31 January 1951, and headed for the United States East Coast for training cruises.

After participating in NATO exercises and a Mediterranean cruise, she returned to the East Coast and was decommissioned at the Boston Navy Yard on 15 December 1953.

In 1973, she began permanent display as a memorial at Battleship Cove in Fall River, Massachusetts, where she is one of the museum's most popular exhibits.