USS Aegir (AS-23) was the lead ship of the Aegir-class submarine tender in the United States Navy. Aegir was laid down on 31 March 1943 under a Maritime Commission contract (MC hull 856) by the Ingalls Shipbuilding Company in Pascagoula, Mississippi and launched on 15 September 1943, sponsored by Mrs. James A. Sweeney. The ship was acquired by the Navy and placed in temporary commission on 20 November 1943 for passage to her conversion yard where she was turned over to the Todd Shipyards Corporation in Brooklyn, New York for conversion to a submarine tender on 3 December 1943. Simultaneously decommissioned and placed in full commission at the Brooklyn Navy Yard on 8 September 1944 with Commander A. L. Prosser in command.