USNS Card was a Bogue-class escort carrier that had served in the United States Navy. In 1946 Card was decommissioned and was transferred to the Atlantic Reserve Fleet. On May 16, 1958, Card re-entered service with the Military Sea Transport Service, under the control of the United States Navy. The ship was manned by a civilian crew and was prefixed "USNS" (United States Naval Ship) instead of "USS" (United States Ship) as it was in service but not commissioned.
With the escalation of the Vietnam War, the United States government stepped up military support for South Vietnam's fight against the Viet Cong. On December 15, 1961, USNS Card left Quonset Point, Rhode Island, with a cargo of H-21 Shawnee helicopters and U.S. soldiers from Fort Devens, Massachusetts, bound for Vietnam. At Subic Bay in the Philippines, the cargo and troops were transferred to USS Princeton, which arrived and unloaded off the coast of Da Nang the following month.
while in service with the United States Navy
From 1961 onwards, Card and USNS Core regularly docked in Saigon to unload heavy artillery, M113 armored personnel carriers, aircraft, helicopters and ammunition for the South Vietnamese government. The Port of Saigon was situated between the Te and Ben Nghe Canals, and was about 700 meters (2,300 ft) wide from one side to the other. To facilitate the arrival of Card and other American ships which pulled into Saigon, the South Vietnamese military often deployed navy vessels to conduct patrols around the port, while the surrounding shores were protected by an elite Army of the Republic of Vietnam (ARVN) Airborne battalion. The port itself was guarded round the clock by Republic of Vietnam National Police, as undercover South Vietnamese agents operated across the river in the Thu Thiem area to disrupt VC activities there. Undeterred by the level of protection which the South Vietnamese government normally afforded to American ships, Tran Hai Phung—commander of the Viet Cong's Saigon-Gia Dinh Military District—ordered the 65th Special Operations Group to attack USNS Card.