USS Pegasus was built in 1939 as SS Rita Maersk by A/A, Helsingør, Denmark. Following the outbreak of World War II in Europe, she sailed to the United States where she operated under charter from the Maritime Commission as Rita Maersk and later as Larwin. After completing two cruises, she was laid up at Boston, Massachusetts, until 18 September 1941 when she was acquired by the United States Navy from the Maritime Commission. Renamed USS Pegasus on 15 October 1941, the cargo ship was converted for U.S. Navy use by Sullivan Drydock and Repair Corporation, New York City, and commissioned at New York on 3 December 1941, Lt. Comdr. William Fly in command.