USS Willoughby, a 1,766-ton motor torpedo boat tender, was built at Houghton, Washington, and was commissioned in June 1944. One of four Barnegat class small seaplane tenders designated during construction for conversion to PT boat tenders, she was reclassified from AVP-57 to AGP-9 in March 1943 just before her keel was laid. Following shakedown training, she departed the West Coast in August 1944 and arrived in September at Mios Woendi in the Southwest Pacific, where she commenced tending a squadron of PT boats. In October she sailed with her sisters Oyster Bay (AGP-6) and Wachapreague (AGP-8), an AVP, and two army craft for Leyte in the Philippines, escorting a group of 45 PT boats in "the largest and longest mass movement of PTs under their own power during the war." A few days after their arrival in the Philippines, 39 of these 45 PT boats played a prominent role in the Battle of Surigao Strait, in which the Japanese lost two battleships, two cruisers, and several destroyers.

Willoughby remained in the Philippine theater for the next seven months, experiencing frequent air raids through the end of 1944 but escaping damage. In November she returned to Mios Woendi and, with her sister Wachapreague and a converted LST, escorted another large group of PTs, 41 boats, to the Philippines. In June 1945 she moved to North Borneo, where she supported PT boats in coastal operations and experienced more air attacks. She remained in the East Indies after the end of the war, taking the surrender of Japanese units and embarking former Allied prisoners of war and internees. Returning to the United States for inactivation, she arrived at Mare Island, California, in December 1945.

Willoughby was decommissioned in June 1946 and was simultaneously transferred to the Coast Guard for use as a weather patrol ship. Renamed USCG Gresham (WAVP-387, later WHEC-387), she served out of Alameda, California, primarily on weather stations, for most of her Coast Guard career. She was decommissioned in May 1973 and sold for scrap in October 1973.