From 5 January to 2 April 1955 Grampus proceeded independently to the Mediterranean Sea, where she "showed the flag" at Algiers, Naples, Barcelona, Malta, Beirut, Monaco, and Gibraltar before returning to Norfolk and her routine of exercises and tests, spaced with regular overhauls at Portsmouth, New Hampshire, and Philadelphia, Pennsylvania.

After refresher training and shakedown in the fall, Grampus operated along the East Coast engaging primarily in ASW exercises.

She departed Norfolk, Virginia, on 13 May 1966 for the eastern Atlantic and Northern European countries to participate in NATO ASW exercises.

Back in Norfolk on 30 August, she resumed operations in the Virginia Capes area and Caribbean Sea until sailing 29 December to Philadelphia, Pennsylvania, for repairs in the naval shipyard.

Grampus was decommissioned and struck from the Naval Vessel Register on 13 May 1972, and sold under the Security Assistance Program to Brazil, where was renamed Rio Grande do Sul (S-11).