The vessel was laid down as the merchant ship Executor on 14 March 1940, under a Maritime Commission contract (MC hull 104), at Quincy, Massachusetts, by the Fore River yard of Bethlehem Steel Co. She was launched on 21 September 1940, sponsored by Mrs. A.R.

The ship was converted at the Tietjen and Lang Dry Dock Co., Hoboken, N.J.; Almaack was commissioned at the Army Transport Service Base, Brooklyn, on 15 June 1941, with Comdr.

Screened by a battleship, three heavy cruisers, and seven destroyers, the convoy included Almaack, a transport, a storeship and an oiler, and the aircraft carrier Wasp (CV-7)—the latter with planes of the 33d Pursuit Squadron (Curtiss P-40s) on board, earmarked for the defense of the base in Iceland.

King, Commander in Chief, United States Atlantic Fleet, agreed to recommend independent routing for fast cargo ships such as Almaack unless "available information indicates undue danger from submarine concentration .

Loaded with a cargo of heavy construction equipment, Almaack sailed from New York on 19 January 1942, as an element of Convoy AT 12: 13 ships carrying 14,688 men—of this number 8,493 were Army troops being transported to Belfast, Northern Ireland, and 1,153 were sailors to man the new naval operating base being established at Derry.

Assigned to Transport Division 2 with Amphibious Forces, Pacific Fleet, Almaack underwent repairs and alterations at the Craig Shipbuilding at Long Beach, before she returned to San Diego on 15 July for landing exercises off the southern California coast.

Returning to the East Coast of the United States and arriving at Norfolk on 12 September, Almaack underwent further alterations and repairs before proceeding to New York to load cargo.

Almaack sighted three more Ju 88s at 10,000 feet (3,000 m) shortly after sunset, and went to general quarters, opening fire with her antiaircraft battery soon thereafter as the three Junkers dive-bombed the nearby Samuel Chase.

Underway at 0530 on 10 November, the cargo ship stood in to Algiers harbor and secured to a berth at the Mole Louis Billiard shortly before the commencement of the forenoon watch.

Bound for the British Isles on the morning of 15 November, Almaack, shortly before 0315, noticed escort vessels on her port beam firing' machine guns; almost simultaneously the convoy commodore called for an immediate right turn.

Over the next several months, Almaack underwent repairs and alterations at Norfolk Navy Yard; during this time she was repainted overall Measure 11, Sea Blue, and received new masts to handle the brood of landing craft assigned the ship.

Sailing as part of Task Force (TF) 53, Almaack reached the transport area for the initial assault on "Jacob" and "Ivan"— islands in Kwajalein Atoll—at 0500 on 31 January.

Proceeding thence to Nouméa, New Caledonia, for liberty, as well as firing and landing exercises, Almaack returned to Guadalcanal (Tulagi), and then to Funafuti, before she pushed on for Canton Island, and a stopover there to load "worn-out equipment" en route back to Hawaii.

Arriving at Honolulu on 10 April 1944, Almaack unloaded the cargo she had brought from Canton and then moved up to Pearl Harbor, where she underwent repairs and alterations and loaded 300 tons of 6-inch cruiser ammunition.

Proceeding back to Pearl Harbor after loading, Almaack then sailed for Lahaina, where she and the other ships slated to take part in the next major amphibious operation conducted rehearsals for it.

Ultimately, the task aided immeasurably by the embarked two platoons of the Army's 311th Port Company, Almaack completed working her cargo by the 24th, unloading the ship in 79 hours.

Taking on board combat equipment of the Army's 77th Division (designated as the reserve for the assault on Guam) the attack cargo ship cleared Honolulu on 9 July for Eniwetok, arriving there on the 17th.

Following that repair period at Pearl, Almaack loaded troops, equipment, and supplies of the Army's 96th Infantry Division, slated to take part in the planned invasion of the island of Yap, in the Carolines.

Almaack's automatic weapons scored hits on the right wing and tail of the "Jill"; shedding parts, the enemy aircraft went out of control about 100 yards (100 m) from Catskill, passed slightly astern of her, and then plunged into the sea, leaving no survivors.

Underway again on the 26th, the attack cargo ship sailed for the Solomons, and reached Empress Augusta Bay on 30 November, commencing loading cargo—vehicles, ammunition, petroleum products, engineering supplies and signal equipment—immediately.

Almaack, assigned to TG 79.1 and carrying elements and equipment of the Army's 37th Infantry Division, cleared Empress Augusta Bay for Lae, New Guinea, where the ship participated in landing exercises.

On S-3 day (6 January 1945), the convoy to which Almaack was attached, steaming through the Mindanao Sea, encountered its first enemy aircraft, a Japanese reconnaissance plane which was being hotly pursued by four F4U Corsairs.

Almaack had a close call as the convoy neared its objective on S-1 day (8 January), when two "Betties" (Mitsubishi G4M Type 1 land attack plane) made a glide-bombing run on the ship, straddling her with three bombs released at 5,000 feet (1,500 m).

Lowering her landing craft within a half-hour, Almaack anchored in transport area "C", Lingayen Gulf, and at 0745 sighted three Japanese planes in the vicinity, one of which crashed the nearby light cruiser USS Columbia (CL-56).

She commenced her initial unloading of equipment from the Army's 148th Regimental Combat Team (RCT) at 0825, shortly after her beach party shoved off to take up its position ashore.

Later, she resumed cargo operations in her number one hold, while a picket boat watch, as well as armed deck sentries, kept a lookout for potential Japanese suicide swimmers.

She remained there until 6 February, when she sailed for Guam to load elements of the 3d Marine Division, in preparation for what would prove to be the last amphibious operation for Almaack in the war—the assault on Iwo Jima.

Almaack arrived in the maneuvering area 125 miles (201 km) southeast of Iwo Jima at 2200, 19 February, and, in company with the other ships in the task group, awaited orders.

Due to the congested beaches, Almaack's loading was delayed until the 24th; that morning the ship put all of her boats in the water to dispatched to attack transports to disembark assault troops.

Discharging her passengers there on the 24th, Almaack shifted down the coast to Albany, California, where she loaded a cargo of petroleum products; she sailed for China on 18 December 1945, and arrived at the North Chinese port of Tientsin on 21 January 1946.