Armored Troop Carriers (ATC), often called Tangos from the phonetic alphabet for T, were LCM-6 landing craft modified for riverine patrol missions.

The MRF began to be organised in late 1966 with the arrival of the 2nd Brigade, 9th Infantry Division at Vung Tau on 19 December 1966.

Like its World War II ancestor, it had a large well deck for transporting troops and a drop-down ramp for landing soldiers on a hostile beach.

At 6 knots (11 km/h; 6.9 mph) with a full fuel load of 450 US gallons (1,700 L; 370 imp gal) of diesel, the Tango could travel 110 nautical miles (200 km; 130 mi) without refueling.

The ATC carried a Navy crew of seven and could accommodate a platoon of 40 soldiers, an M113 armored personnel carrier, or a 105mm howitzer with a prime mover.