USS Tracer ( AGR - 15 ) USS " Tracer " ( AGR - 15 ) – also known as USS " Interrupter " ( AGR - 15 ) – was a " Guardian " - class radar picket ship acquired by the U . S . Navy in 1957 from the " mothballed " reserve fleet . 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 and Liberty ship built in Florida . " William J . Riddle " — a " Liberty ship " ; - - was laid down under a U . S . Maritime Commission contract ( MC hull E - 2340 ) on 24 December 1944 at Panama City , Florida , by the J . A . Jones Construction Co . , Inc . ; launched on 31 January 1945 ; sponsored by Mrs . Marion Harders ; and , upon completion in early 1945 , was delivered to the War Shipping Administration , Maritime Commission . World War II - related service . " William J . Riddle " operated with Moore - McCormack Lines and the Waterman Steamship Corporation from 1945 to 1947 . When hostilities ended in the Par East in mid - August 1945 , the " Liberty ship " was steaming from Hawaii to the Philippines . Converted to a cattle carrier the following year , she operated as such through the end of 1946 . 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 the U . S . Maritime Commission ' s National Defense Reserve Fleet and berthed in the James River , Virginia . She remained there for 10 years . Conversion to radar picket ship . The Navy selected " William J . Riddle " for conversion to a radar picket ship in May 1957 . Towed to the Charleston Naval Shipyard ( South Carolina ) soon thereafter , conversion work began on 24 May 1957 . Renamed " Interrupter " , and classified as " AGR - 15 " , the erstwhile " Liberty " was commissioned at Charleston , South Carolina , 16 October 1958 , Lt . Comdr . George S . Harrison in command . Following shakedown in Guantanamo Bay , Cuba , and post - shakedown availability at her conversion yard , " Interrupter " sailed for the Pacific Ocean . 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 . Fitted out with the latest radar detection equipment , " Interrupter " and her seven " Guardian " - class sister ships were designed to serve as the seaborne eyes of the North American Air Defense Command — the naval link in the chain of early - warning stations covering the Pacific approaches to the United States . Her mission was to " detect , report , and track enemy airborne threats approaching by overseas routes and to control the intercepts used to destroy such threats . " 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 . In addition , " Interrupter ' s " , officers and men familiarized themselves with the Air Force ' s part in this vital mission . On 6 March 1959 , " Interrupter " sailed from San Francisco on her first barrier patrol . Solving the name problem . On 4 September 1959 , " Interrupter " was renamed " Tracer " to eliminate confusion with some of her sister ships with similarly sounding names . Between 1959 and 1965 , " Tracer " conducted patrols at sea , at various picket stations in the Western Contiguous Radar Line . The ship proved to be an efficient vessel and received awards for administrative and operational efficiency on several occasions . As more sophisticated early - warning systems came into operational use , the need for the " AGR ' s " diminished accordingly . Deactivation . Deactivated in 1965 , " Tracer ' s " name was struck from the Navy List on 1 September 1965 . She was then transferred to the U . S . Maritime Commission and laid up at Suisun Bay , California , where she remained until sold , 15 July 1974 . Before being scrapped in China in 2000 , " Tracer " – renamed " Unisea " – served as a fish processing plant in Unalaska , Alaska . Honors and awards . " Tracer " personnel qualified for the following medal :