USS Leonis (AK-128) was a Crater-class cargo ship in service with the United States Navy in World War II. It was the only ship of the Navy to have borne this name, the Latin form of the northern constellation Leo.
Leonis was laid down 21 November 1942 as liberty ship SS Key Pittman (MCE hull 512) by Permanente Metals Corporation, Richmond, California, under a Maritime Commission contract in 1943; launched 22 December 1942 acquired by the Navy 6 October 1943; renamed Leonis 11 October and commissioned 25 October 1943; Lt. Comdr. A. J. Barkowsky in command.
After shakedown along the west coast, Leonis departed San Pedro 6 December with cargo for the Pacific islands. Arriving Pago Pago, American Samoa, on 22 December, she remained there until 1 January 1944 when she sailed for Funafuti Atoll, Ellice Islands. From January to April Leonis shuttled cargo among the Marshall, Gilbert, and Ellice Islands before sailing for Pearl Harbor 19 April.
Assigned to the V Amphibious Corps, Leonis loaded troops at Pearl Harbor and departed the Hawaiian Islands 29 May. The destination was the Marianas needed "to secure control of sea communications through the central Pacific for the support of further attacks on the Japanese." Leonis arrived in the transport area off Saipan with reinforcements and cargo 20 June, 5 days after the initial landings. Remaining off Saipan until 3 July, she made a brief stop at Eniwetok, then returned to Pearl Harbor on 27 July.
Following training and repairs, the cargo ship departed Pearl Harbor 20 August to join the forces preparing for the Palau Islands campaign. After stopovers at Kwajalein and Manus, Leonis arrived Kossal Passage 20 September with men and equipment needed to capture the islands. The Palaus were utilized as an advance base for the Leyte operations, and Leonis remained off Peleliu until mid-November.
After loading Marines and other passengers at Peleliu, the Russell Islands, Tulagi, and Guadalcanal, the cargo ship sailed for the United States, arriving San Francisco 18 December. Reloading with battle supplies, Leonis departed San Francisco 11 January 1945 to join the Western Pacific Forces as a fleet issue ship.
Touching the Marshalls and Carolinas en route, she arrived San Pedro Bay, Leyte Gulf, 28 February. For the rest of the war she remained primarily in the Philippines supplying the fleet with dry stores and medical provisions. Following the Japanese surrender, Leonis departed Leyte 4 September, arriving San Pedro, California, 1 month later. Sailing again 15 October, the veteran cargo ship proceeded toward the East Coast, arriving Norfolk, Virginia 6 November. Leonis decommissioned there 5 December 1945 and was returned to WSA the 9 December.
Leonis received two battle stars for World War II service.
(AK-128: dp. 14,350 (tl.) : l. 441'6"; dr. 28'4"; s. 12.5 k.; cpl. 234; a. 1 4", 1 3", 8 20mm.; cl. Crater; T. EC2-SC1)