After shakedown, Greenlet conducted patrol and escort runs out of San Diego, California before sailing for Pearl Harbor, Territory of Hawaii on 24 July.

As the progress of the war advanced steadily across the Pacific, she sailed to Guam on 21 December 1944 to carry out submarine training closer to the patrol areas.

Eleven of the submarines trained by Greenlet were lost during the war, but her charges sank more than 2,797,000 tons of Japanese military and merchant shipping.

She reached Sagami Wan, Honshū, on 28 August; entered Tokyo Bay the following day; and was present during the signing of the Japanese surrender on 2 September.

Sailing for Pearl Harbor on 6 January 1951, she served there throughout the remainder of the Korean War and continued to provide assistance in the training of submarine crews.

During Greenlet's final deployment to WestPac in 1969–1970, she was ordered to the Gulf of Tonkin to salvage a Grumman C-2 aircraft that has crashed with 26 persons on board and sunk in 290 feet (88 m) of water.

Greenlet was awarded a Meritorious Unit Commendation (MUC) and the Vietnam Service Medal for the Fall and Winter Campaigns of 1969.

The citation for the MUC reads in part, "For meritorious service from 11 October to 14 April 1970 while serving with the SEVENTH Fleet as the ready Submarine Rescue Ship and Deep-Diving Platform for deep salvage and recovery operations.

This operation was terminated by Commander SEVENTH Fleet due to the untenable area hazards caused by continued and pronounced weather deterioration.