William J. Riddle, a "Liberty ship", was laid down under a Maritime Commission contract (MC hull E-2340) on 24 December 1944 at Panama City, Fla., 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.
William J. Riddle operated with Moore-McCormack Lines and the Waterman Steamship Corp. 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 of 1947, she voyaged to European and Mediterranean ports until the summer of 1947 when she was laid up in the Maritime Commission's National Defense Reserve Fleet and berthed in the James River, Va. She remained there for 10 years.
The Navy selected William J. Riddle for conversion to a radar picket ship in May of 1957. Towed to the Charleston (S.C.) Naval Shipyard soon thereafter, conversion work began on 24 May 1957. Renamed Interrupter, and classified as AGR-15, the erstwhile "Liberty" was commissioned at Charleston 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. She transited the Panama Canal on 26 January 1959 and arrived at her home port, San Francisco, Calif., 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 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.
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. Deactivated in 1965, Tracer's name was struck from the Navy list on 1 September 1965. She was then transferred to the Maritime Commission and laid up at Suisun Bay, Calif., where she remained through the late 1960's.