USS Markab (AD-21) was a Hamul-class destroyer tender named for Markab, the third-brightest star in the constellation Pegasus.

The ship was built as the cargo ship Mormacpenn by Ingalls Shipbuilding Company of Pascagoula, Mississippi and launched 21 December 1940. A ship named Mormacpenn launched the previous year had been acquired by the Navy to become the USS Griffin. The later Mormacpenn, sponsored at launch by the wife of the General Counsel of the Maritime Commission, Mrs. Carl F. Farbach, was intended for service on the South American routes of the American Republics Line.

The ship was acquired by the United States Navy on 2 June 1941 before any commercial service at Charleston, South Carolina; and commissioned as USS Markab (AK 31) on 15 June 1941 with Commander Allen D. Brown in command

World War II

Cargo ship, 1941–1942

Markab operated with Atlantic amphibious forces in the Hampton Roads area until 1 October 1941. She then loaded cargo at Jersey City, New Jersey for delivery to American troops recently stationed in Greenland. Returning to Brooklyn, New York on 21 November, she took on board supplies for distribution to various bases in the Caribbean. World War II engulfed the United States before Markab steamed into Ensenada Honda, Puerto Rico, her first port of call. The new wartime demands on the Navy caused this voyage to terminate at Mobile, Alabama on 8 January 1942 where she was converted to a destroyer tender. Sixteen days later she was redesignated AD-21, but it was 27 September before Commander Brown again commanded a fully commissioned vessel.

Destroyer tender, 1942–1947

After shakedown Markab transited the Panama Canal on 27 October to join Destroyer Force, Pacific Fleet at Pearl Harbor. Ships recently returned from the battle for the Solomon Islands made use of her facilities for three months prior to her departure on 6 February 1943 to service the North Pacific Force. In the year she remained in the Aleutians, she rendered noteworthy service in helping to prepare vessels for both the Attu and Kiska invasions. Steaming to San Francisco late in January, 1944 the ship prepared for an even more extensive Pacific tour.

She departed the West Coast on 26 February and worked her way toward the war zone. As a part of Service Squadron 10, Markab overhauled, repaired, and replenished destroyers and destroyer escorts at Pearl Harbor, Majuro, and Eniwetok in the Marshall Islands, and Ulithi in the Carolines. Having assisted in preparing and sustaining the ships fighting in the bloody conquests of the Marianas and Iwo Jima, she sailed for the Philippines on 16 February 1945. Her work force now overhauled and readied landing craft for the assault on Okinawa. During June she played an important part in preparing TF 38 for the last great raids on Japan.

Following the Japanese surrender, Markab refitted and restocked ships bound for the occupation areas of Japan, Korea, and China. Steaming in their wake, she arrived Sasebo, Japan on 1 November and early in January 1946 joined the 7th Fleet at Shanghai, China. Her services in the western Pacific ended 2 April as Markab commenced the long voyage home for inactivation. The ship off loaded at New Orleans beginning 6 May. At Orange, Texas on January, 1947 she decommissioned and entered the Atlantic Reserve Fleet.