Shortly after a 10-day shakedown period, MANATEE departed the Chesapeake Bay area for the Dutch West Indies. Loading at that oil center, she got underway for the Panama Canal and the Pacific. Arriving at Eniwetok 16 June, she replenished the amphibious forces then invading Saipan. She shuttled from Eniwetok to the fueling areas throughout the campaigns for Saipan, Tinian, and Guam, until moving to Manus, largest of the Admiralties, 20 August. From Manus, she continued carrying fuel and other supplies to fast carrier group through the battle for Pelelieu and the first phase of the Philippine campaign. By 20 October, when MANATEE departed Manus for the last time, Ulithi Atoll had been secured and had become the center for the fleet oilers.
From the Admiralties, MANATEE proceeded north to support the forces then covering the Leyte landings. Her fueling activities kept her in the Philippines until late February 1945, when she returned to Ulithi. From Ulithi she steamed back to Leyte Gulf to fuel the amphibious forces gathering for the Okinawa campaign. On 28 March, she began shuttling oil from Ulithi to the carrier groups operating in the Okinawa invasion. She continued to work this supply line until the securing of the island 21 June, 82 days after the landings.
On 2 July, MANATEE was ordered to join other fast oilers in lending close support to carrier groups during strikes on the Japanese home islands. The oilers moving at night to rendezvous with the carriers, refueled them within 200 miles of the enemy's coastline and then retired. Efficient organization and rapid routing of empty oilers to Ulithi for refueling resulted in an ample supply of fuel oil for the fleet carrier forces.
With the cessation of hostilities 15 August, MANATEE sailed for Ulithi en route to San Pedro, Calif., arriving 7 October 1945. The oiler soon again departed the west coast for the Far East, returning to the western Pacific at the end of November to support the occupation operations. She made three round-trip voyages between the oil ports on the Persian Gulf and Tokyo before sailing for Hawaii. Overhaul completed at Pearl Harbor she departed Hawaii 11 September 1947 for the Persian Gulf. On this voyage the oiler was loaded at Ras Tanura, Arabia, and off-loaded at Norfolk, having arrived 17 November via the Suez Canal and Gibraltar.
Early the next year she departed for the Persian Gulf and made two voyages to Japan from Bahrain before returning to Norfolk 22 April 1948. She then commenced shuttle trips between Aruba, Bayonne, N.J., and Argentia. Departing the latter port 2 June, she steamed via the Persian Gulf and Japan for California, arriving 20 August.
On 6 January 1949, the oiler departed Long Beach for the western Pacific. Having completed three round trip cruises between Sasebo and the Persian Gulf, she returned to the west coast 17 July. At San Francisco, her rig for fueling at sea was removed and MANATEE began 20 months service as an MSTS vessel. At first operating along the west coast, her assignments soon extended to the Caribbean, gulf and east coast ports. On 27 October, she departed Boston for Ras Tanura on the Persian Gulf. By 17 February, having called at Manila, Yokosuka, and Pearl Harbor, she was back at Long Beach. There she was re-equipped for fueling at sea and again became a fleet oiler to support the fleet in operations to thwart Communist aggression in Korea.
On 17 march 1951, MANATEE arrived in Japanese waters to begin her first annual WestPac deployment. After brief periods at Tokuyama and Sasebo, she received orders to replenish the Taiwan Straits Patrol. She returned to Sasebo 20 May and commenced servicing the Navy's ships in combat areas off the Korean coast. She continued to operate out of Sasebo for the next 5 months, returning to Long Beach 11 August. Her next two WestPac deployments, 21 March to 19 October 1952 and 6 February to 29 July 1953, followed the same pattern, 1 month with the Taiwan Straits Patrol and the remainder of the tour operating out of Sasebo in support of Korean operations.
For the next 5 years MANATEE's operating schedule continued to be 6 months in the western Pacific, 6 months on the west coast. During this period, she participated in fleet operations and in underway training exercises, as well as undergoing regular overhauls. Included in her Pacific deployment for 1954 was the replenishment of the ships present in the Marshall Islands for the March hydrogen bomb tests.
Scheduled for only 4 months deployment in the western Pacific in 1958, mid-May through mid-September, MANATEE remained an extra month to service the ships called to the area during the Formosa crisis over Quemoy and Matsu islands. The following year, after her 4 months WestPac duty, MANATEE was chosen, because of constantly efficient service, to take part in a joint Canadian- American replenishment demonstration held 8 October 1959 for the 14th Annual Conference of the National Defense Transportation Association. In the year that followed MANATEE continued to alternate duty on the west coast with Far Eastern service. She was one of seven ships chosen to visit Australia, 29 April - 13 May, for the 1963 Coral Sea celebration.
With the stepped up operations in Vietnam, MANATEE's 1964 WestPac tour was extended to 8 1/2 months, May 1963 through January 1965. During this period she operated principally in the South China Sea. South China Sea operations also occupied most of her 1966, 1967, and 1968 tours, replenishing the ships of the 7th Fleet on patrol in that area in support of the struggle against Communist aggression in Vietnam. Her final WestPac tour commenced
on 13 May 1972 and lasted 10 months. MANATEE was decommissioned in July 1973.
MANATEE received eight battle stars for World War II service and six for Korean service.