After her Army career, she was transferred to the United States Air Force on 1 October 1963, and was redesignated USAFS American Mariner.

After Air Force service, she was transferred to the United States Navy on 7 January 1964 and designated USNS American Mariner (T-AGM-12).

On 1 October 1966 title to the vessel was transferred to the Navy for disposal and later in the month she was scuttled in shallow water in the Chesapeake Bay about 5 nautical miles (9.3 km) northwest of Ewell, Smith Island, Maryland, for use for a target ship.

[4] She appears to have been the only ship to have served in the U.S. Coast Guard, the U.S. Army, the U.S. Air Force, and the U.S. Navy after being built for service with the United States Merchant Marine.

The keel for SS George Calvert (build number 2007/MC Hull 20) was laid on 15 August 1941 in the Bethlehem-Fairfield Shipyard, Baltimore, Maryland.

During her years on the DAMP Project USAS American Mariner operated various types of long-distance, narrow-beam radars to gather data on intercontinental ballistic missiles.

This, if such data could be provided and fed into the computers of that era, would lead to the development of American anti-ballistic-missile defense systems, such as Nike-Zeus, which was a part of Project Nike.

While investigating reports of foreign missile testing in the North Pacific Ocean in November 1962, USAS American Mariner became caught up in Typhoon Karen, which caused significant rolling, and some flooding, of the top heavy ship, which was quickly repaired.

During Wally Schirra's MA-8 transits over the Pacific Ocean, USAS American Mariner successfully provided radar track of the capsule.

While performing her missile-tracking operations, American Mariner was re-provisioned in various ports in both the Atlantic and Pacific Oceans: In the Atlantic Ocean, shore-side support was generally provided at San Juan, Puerto Rico; Antigua Island; Chagaramus, Trinidad; Recife, Brazil; Monrovia, Liberia; Dakar, Senegal; and Cape Town, South Africa.

Extensive shipyard overhauls and drydocking were conducted in Brooklyn, New York; Baltimore, Maryland; San Juan, Puerto Rico; Long Beach, California; Pearl Harbor, Hawaii and Dakar in Senegal, Africa.

Prior to participating in nuclear testing operations during the Spring and Fall of 1962 under Operation Dominic, USAS American Mariner was outfitted at Pearl Harbor, Hawaii, with protective anti-radiation equipment, including emergency warning lights and a water spraying system that, when turned on during an atomic event, would cover the ship with a fine spray of water intended to remove and wash away nuclear contamination.