USS Tracer (AGR-15) was a Guardian-class radar picket ship, converted from a Liberty Ship, acquired by the US Navy in 1957. She was reconfigured as a radar picket ship and assigned to radar picket duty in the North Pacific Ocean as part of the Distant Early Warning Line. 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)