The United States Navy, much like the French Navy before it during the First Indochina War, saw the importance of controlling and using the many streams and rivers of South Vietnam for war fighting and resupply. The purpose of the Armored Troop Carrier (or "ATC") was therefore twofold - first to move US Army and ARVN troops and, second, to service the fire team boats and other gasoline-powered watercraft on the rivers of Viet Nam. During a standard operation, troops were carried into battle in the Navy's ATCs, which were conventional landing craft, armored to safeguard against heavy fire they often were exposed to from canceled enemy positions onshore. These armored boats could carry a fully equipped infantrymen platoon of 40 men on any waterway with a depth of 5 feet or more.
The ATC boats converted from LCM-6 landing craft developed in the 1950s for ship-to-ship and ship-to-shore use. The converted LCM designs added 0.25 inch armor plating in many areas to protect the superstructure from critical damage caused by rockets. The upgraded armored ATC made up about half of the river craft deployed by the United States during the Vietnam War, in effect making the ATC the "workhorse" of the river war. Some ATCs had helicopter decks added and became ATC(H). These installations allowed helicopters to land on the boats themselves for swift evacuation of wounded soldiers. The Mobile Riverine Force (MRF) started with three basic boat types: (1) the ATC boat ("Tango Boat") - this served as the most useful boat; (2) the "Monitor", a floating artillery platform of the MRF and, (3) the Command and Communications Boat (CCB), the so-called "Charlie Boat". Each squadron of boats had a Tango boat converted into a boat for refueling to be used by all of the above.
The ATCs fuel capacity (using fuel oil or gasoline) was 1,200 gallons with space for 300 gallons of lube oil with a mixing tank holding 500 gallons. The boat was equipped with a portable tank and transfer pump that required hoses for the fuel exchange. The ATC full load displacement was 155,000 lbs with a cargo weight of 130,000 lbs. A sling was installed for hoisting fuel containers onboard. She maintained a semi-flat bottom with 2 x 6-cylinder diesel engines each having 225 horsepower at 2,100 rpm for emergency use and 165 horsepower at 1,800 rpm for continued use. ATCs fielded 2 x 24-inch D by 17-inch P by a 2-inch bore with a right-hand rotation propellers. The cargo well was 9'6" x 22'6" with a clear overhead and 9'6" x 31' 6" with a clear dock.
All Tango boats had a distinctive lowering bow ramp used to deploy troops and load cargo to and from shorelines. The ATC could provide close support against enemy fire due to a shield of hardened steel armor. The vessel could carry an arsenal of weapons that made her available for most defensive- and offensive-minded missions. ATCs were typically fitted with 4 x 7.62mm M60 general purpose machine guns and 2 x 12.7mm Browning M2 heavy machine guns, 1 x 40mm Mk 19 rapid-fire automatic grenade launchers and 2 x 20mm cannons, these protected in armored pill boxes. The crew of seven also carried their personal weapons and large supplies of ammunition was kept on board. If the Monitor river craft were considered the "battleships" of Vietnam rivers then the Tango ATC boats were the "heavy cruisers".
The Tango boats participated in a memorable chapter of the United States Navy's river warfare that was a hard fought effort for control of the "green" and "brown" waterways of the Republic of Vietnam. The US Army's Mobile Riverine Force used the ATC to transport the Riverine Infantry Force throughout the Mekong Delta. In the early part of the war, Tango boats mainly transported troops of the 9th Infantry Division. When the decision came down to integrate, Vietnamese Army and Marine troops replaced the Americans on these Tango boats.
The Viet Cong guerrillas operated on the river on a daily basis and this led to fierce gun battles at very close quarters. The guerrillas used a multitude of boats (called "junks" and "sampans") that were capable of navigating in only a few inches of water and could travel practically unseen and unheard near the banks of the rivers. However, also operating in these inland river areas was the joint Army and Navy Mobile Riverine Force. This force consisted of ATC's and heavily armed and armored monitors along with support boats that moved combat troops from the US Army's 9th Infantry Division into combat.
The ACT's were able to deploy troops on the flanks and to the rear of communist elements in an effort to defeat the enemy forces. After many years of war, the enemy had begun to find ways to counter the allied river patrol effort - the Viet Cong started using smaller rivers and canals to move their supplies. As such, the main force of the North Vietnamese Army and Viet Cong learned to avoid direct contact with the more powerful Mobile Riverine Force.
To secure the Mekong Delta in Vietnam, the American and Vietnamese river units fought well and hard against a tough Vietnamese communist enemy. In 1975 the Vietnam War ended in failure for the Republic of Vietnam and, by extension, the United States. However, the experience and brave work of the ATC crews, and that of her sister type ships, provided the military with valuable knowledge of riverine warfare for possible future application.