After completing sea trials in the New London, and Massachusetts Bay areas, T-1 departed in February 1954 for Key West, Florida.

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.

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.

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.

After that, she remained in service with a reduced crew and conducted junior officer and midshipman training on the surface regularly through October 1972.

Mackerel and her sister USS Marlin (SST-2) were decommissioned on 31 January 1973 in a dual ceremony at Naval Station Key West.