She then was redesignated as a United States Naval Ship, assigned to the Military Sealift Command, and served in a non-commissioned status with a mostly civilian crew as USNS San Diego (T-AFS-6) until 1997.

[1][2] After shakedown and refresher training in late 1969, San Diego began a seven-month, deployment to the Mediterranean in support of the United States Sixth Fleet.

During this tour of duty, she earned the Supply Efficiency "E," rescued sailors from a burning Greek freighter, and represented the Sixth Fleet at Admiral Farragut Day at Menorca in Spain's Balearic Islands.

[citation needed] During the three Mediterranean cruises from 1973 to 1976, USS San Diego stopped in ports from Lisbon, Portugal, to the Greek Island of Corfu, just off the coast of Albania.

[citation needed] On its next deployment to the Mediterranean Sea from October 1976 to March 1977,[citation needed] San Diego serviced task groups led by aircraft carriers USS Franklin D. Roosevelt (CV 42), USS John F. Kennedy (CV 67), USS Nimitz (CV 68) as well as the fleet Amphibious Task Group on a rotating basis, by Underway and Vertical Replenishment, and also provided in-port Vertical Replenishment to Sixth Fleet auxiliary forces docked at La Maddalena, Corsica and Souda Bay, Crete.

[citation needed] On 17 January 1989, San Diego was involved in a collision with the submarine USS Norfolk (SSN-714) in the Thimble Shoal channel,[3] as both vessels were headed to sea.