Barnstable was an Alpine-class attack transport. Western Pipe and Steel launched her at Los Angeles on 5 August 1943 as Sea Snapper, and Miss Jean Watts sponsored her. The Navy acquired her on a loan charter on 30 October 1943 and commissioned her that day, then took her out of commission on 3 November. Commercial Iron Works at Portland, Oregon, fitted her out as an attack transport. Captain T. M. Stokes recommissioned her on 22 May 1944.
Pearl Harbor on 30 July 1944 was where she joined Transport Division 32. Troops and cargo aboard, she went to Guadalcanal for landing exercises from 24 August to 8 September, ahead of the Palau assault. She arrived at Peleliu on 15 September and remained until 21 September, Ulithi was occupied with her help from 23 to 25 September. Back at Manus she loaded again and entered Leyte Gulf on 20 October. Troops went off for the assault waves, and cargo kept moving ashore through the day. She departed on the 21st and was in the Palau Islands on 23 October.
Troop and cargo runs linked New Caledonia with the Admiralty Islands. She was back at Leyte with reinforcements from 19 to 29 November. New Guinea was the next wait, until she embarked for Lingayen Gulf. Arrival was on 9 January 1945, and the troops and cargo went ashore the following day. Several further trips brought reinforcements to the Philippines. From 1 to 5 April she was in the initial landings on Okinawa.
After Okinawa she returned to the west coast, underwent repairs, embarked replacements, and went back to Manila. Logistic runs from Manila to New Guinea followed. When hostilities ceased she joined the occupation of Japan from 12 to 26 October 1945, two trips from the Philippines to Japan with Army troops. California again on 17 November 1945. She operated on the west coast until January 1946, reached the east coast in February, and began a pre-inactivation overhaul. Decommissioning was on 25 March 1946. The Maritime Commission got her back the next day. Four battle stars were awarded.