The USAS American Mariner was a converted research vessel that operated under this name from 1959 until 1963. It was originally laid down in 1941 by the Bethlehem-Fairfield Shipyard in Baltimore, Maryland, as the Liberty Ship SS George Calvert (MC #20) but it was redesigned during its construction to a training ship for the US Coast Guard and operated as such until 1953 when it was placed in the Hudson River reserve fleet.
The vessel was removed from the fleet, transferred to the US Army, and equipped with a high-tech radar tracking device. The ship was operated by the Mathiesen Tankers Industry and the RCA Service Company which provided the necessary personnel and equipment for the ship’s new DAMP Project task. While working on this assignment, the USAS American Mariner took parts in various ballistic missiles tests performed in the Atlantic and Pacific Oceans. The aim was to gather radar signature data of intercontinental ballistic missiles and figure out if ballistic missiles could be identified while outside the atmosphere. While carrying out the test operations in the Pacific Ocean, the ship was temporarily assigned to NASA to provide radar tracking for their Mercury program. The USAS American Mariner operated as a radar tracking ship until mid-1964 when it was replaced by two US Air Force Ships. The ship was sunk in shallow waters with demolition charges and subsequently used for target practice by naval aviators until 1971. The ship's remains can still be seen in the Chesapeake Bay between Point Lookout and Smith Island.