Forces from the Third Squadron, 5th Cavalry Regiment were entrusted with the securing of Fire Support Base 20, around 1.5 km north of the village of Bàu Bàng.

During the evening of 19 March, elements of the VC 9th Division attacked the base with machine guns, mortars, rockets and small arms fire.

With the help of artillery and air strikes, as well as flares and aerial searchlights to spot their enemies, the Americans repelled the Viet Cong.

[3] Fire Support Base 20 was located in relatively flat terrain 1.5 km north of the village of Ap Bau Bang and immediately west of Route 13.

[3] American intelligence sources had indicated that the area was densely populated with VC guerrillas, noting the existence of a well-used trail to the north of Fire Support Base 20 which ran east and west.

Alcala sent his 2nd Platoon commanded by First Lieutenant Harlan E. Short to establish an ambush along the trail at a point 1.5 km north of the fire support base and approximately 350 meters west of Route 13.

The probe was spearheaded by a herd of fifteen belled cattle driven across Route 13 at a point 150 meters northeast of the perimeter.

At 2300 the VC opened fire on the northeast section of the perimeter with a wheel-mounted .50-caliber machine gun positioned on the railway embankment.

[3]: 131 The Americans concluded that the VC mortar positions were 1.5–2 kilometers west of Ap Bau Bang in and around an old village that had been destroyed.

The positions were located by radar from Lai Khe, although one officer thought that airborne artillery observers seeing the flashes were more effective.

[3]: 131  Throughout the mortar and antitank bombardment, Alcala maintained radio contact with his squadron commander, Lieutenant Colonel Sidney S. Haszard, who was located to the south.

These were the troops of the 273rd Regiment, who had been waiting in position in the rubber trees before moving forward under mortar fire cover, wearing dark clothes.

Haszard noted the growing size of the VC offensive and decided to move with his command element to A Troop's position.

The 3rd Platoon of Troop C, moved up Route 13 from their position five kilometers to the south, driving through a barrage of fire before reaching the base perimeter at 0127.

Several VC who attempted to remove the .50-caliber machine gun from one of the burning tracks of Festa's unit were killed, as were others trying to storm the foxholes containing the wounded.

Initially the artillery covered the northwest, west, and southwest sides of the perimeter while aircraft attacked on a north–south axis east of Route 13.

At 0330 the VC fire eased; resupply of the units and evacuation of the wounded was completed during the next 75 minutes while the artillery and air strikes continued.

[3]: 134 During the battle of Ap Bau Bang II, the Americans claimed to have killed at least 227 VC and captured 3, as well as much equipment and weapons.

[3]: 135 Although more infantry than usual were killed by small arms fire, they were attacking cavalry and armored units, most VC deaths in this battle still resulted from artillery and air strikes.

[3]: 135   This article incorporates public domain material from websites or documents of the United States Army Center of Military History.