USS Delphinus (AF-24) was built in 1915 as SS San Mateo by Workman Clark and Co., Ltd., Belfast, Northern Ireland; acquired by the U.S. Navy 11 August 1942; and commissioned the same day as San Mateo.

Departing San Francisco, California, 12 September 1942, Delphinus arrived at Auckland, New Zealand, 4 October.

After calling at Manila in January 1946, Delphinus sailed for the west coast, arriving at San Francisco, California, 23 February.

For a brief period she carried cargo along the west coast and to Pearl Harbor, then sailed to New Orleans, Louisiana.

Delphinus was decommissioned on 8 May 1946 in New Orleans, and was delivered to the War Shipping Administration the same day.