Because of the closeness of the sound of names issued for radar picket ships at the time, Interrupter had her name changed by the Navy to Tracer so as not to confuse her with USS Interdictor (AGR-13) and USS Interpreter (AGR-14) Tracer (AGR-15) was laid down on 24 December 1944, under a Maritime Commission (MARCOM) contract, MC hull 2340, as the Liberty Ship Dudley H. Thomas, by J.A.

Changed back to a dry cargo carrier by March 1947, she voyaged to European and Mediterranean ports until the summer of 1947, when she was laid up in MARCOM's James River Reserve Fleet, Lee Hall, Virginia.

She transited the Panama Canal, on 26 January 1959, and arrived at her home port, San Francisco, California, on 12 February, the sixth AGR to join newly formed Radar Picket Squadron 1.

[5] Fitted out with the latest radar detection equipment, Interrupter and her seven Guardian-class radar picket ship sister ships were designed to serve as the seaborne eyes of the North American Air Defense Command (CONAD), the naval link in the chain of early-warning stations covering the Pacific approaches to the United States.

"[5] Before putting to sea for her first patrol, she conducted training evolutions with U.S. Air Force officers embarked on board for familiarization with the ship's mission.