Operation Atlanta was a road security operation in Đồng Nai Province carried out by the 11th Armored Cavalry Regiment (11th ACR) from 19 October to December 1966 during the Vietnam War and was the first major combat operation of the 11th ACR in the war.
Background The objective of the operation was to clear and secure lines of communication in three provinces near Saigon and to secure the new Blackhorse Base Camp south of Xuan Loc. At first the operation was limited to clearing and securing Highway 1 from Xuan Loc to Bien Hoa and Route 2 to the base camp. As the operation continued, however, the 11th ACR extended its operations away from the roads and throughout the area. Regimental experience varied from roadrunner and convoy escort duties to cordon and search operations in which the squadrons sealed off an area and then worked, both mounted and dismounted, to drive out the Viet Cong (VC).
It was during the operation that the 11th ACR fought its first major battle. Twice the VC tried to ambush and destroy resupply convoys escorted by units of the 1st Squadron, but in both attempts was defeated by the firepower and maneuverability of the cavalry.
Operation Battle of Ap Hung Nghia On 20 November, two battalions and headquarters of the VC 274th Regiment, the battle-hardened Dong Nai Regiment, moved into ambush positions along Highway 1, west of Xuan Loc. Midway between the provincial capitals of Bien Hoa and Xuan Loc, Highway 1 dropped sharply to a stream bed and then rose to a gently rolling plateau. A dirt road running north and south intersected Highway 1 at this point. Low hills rising only 10-20 meters above the road level began about 180 meters from the highway on both sides. On the north side of the highway, grass high enough to hide a standing man covered the ground. Rising like an island in the sea of grass was an expanse of jungle 1,000 meters square, beginning at the north-south dirt road and running parallel to Highway 1, 300 meters north of the edge of the highway. Along the south side of the highway a wall of jungle had grown up around the trees of an old rubber plantation stretching from the province boundary east for 1,000 meters and ending abruptly at a banana grove. The banana grove lined the south side of the highway for 300 meters before it gave way to an open area ending at the hamlet of Ap Hung Nghia ().
Because the jungle and banana grove offered concealment for approach and withdrawal, the VC commander placed his main force of over a thousand men on the south side of the road, camouflaged and ready to fire automatic weapons and antitank rockets point-blank onto the highway. The ambush extended from just inside the west end of the jungle to the outskirts of Ap Hung Nghia, a distance of 1,500 meters. To handle any US troops who might dismount and take refuge on the north side of the road, the VC commander deployed infantrymen alone or in groups of two or three across the highway in the tall grass. In the classic manner of VC ambush forces, heavy weapons marked both ends of the killing zone. A 75mm recoilless rifle, positioned less than from the road, marked the beginning of the killing zone, just inside the west end of the jungle close by the banana grove. A second 75mm recoilless rifle dominated the road in the eastern half of the killing zone from the forward slope of a slight hill just to the east of the banana grove. A 57mm recoilless rifle farther up the hill, three hundred meters to the east, and an 82mm mortar deep in the jungle were to provide supporting fire. Heavy machine guns hidden in huts scattered through the killing zone were to engage American helicopters and jets. Regimental headquarters operated on the crest of a hill 500 meters west of Ap Hung Nghia, overlooking the entire section of road in the killing zone. Once the ambush was executed the 274th Regiment was to withdraw to railroad tracks parallel to and a thousand meters south of the highway, then along a trail leading due south under a heavy canopy of jungle. Bunkers along the trail for a distance of 2km would provide cover against air attack, while bunkers at the beginning of the trail and a hundred meters south of the railroad tracks would provide defensive positions for a delaying force.
By 06:00 on 21 November most of the convoy’s trucks waited at the starting point at Long Binh Post, for the movement of the 1st Squadron 11th ACR to their new home at Blackhorse Base Camp with departure scheduled for 07:00. However, as the departure was delayed the convoy grew as more vehicles joined it. At 08:40 the convoy escort commander 1st Lieutenant Neil Keltner, commanding the 1st Platoon, Troop C, 1st Squadron, gathered the vehicles for his escort, four ACAVs from his platoon and four from Troop C's 2nd Platoon and an ACAV from Troop A that had missed that troop's move the preceding day. Captain Robert Smith, the Forward air controller (FAC) in a Cessna O-1 Bird Dog was circling above the convoy that now consisted of over 80 vehicles. For the march, Keltner placed his ACAVs in pairs: a pair at the head and rear of the column and at two points equidistant within the column. At 09:20 Lieutenant Keltner gave the signal to move out.
As the convoy passed through the village of Hố Nai, a VC observation post flashed word to the 274th Regiment that the convoy was on the way. Haphazardly formed, lacking unit integrity, the convoy was by its very nature difficult to protect. Gaps within the column began to develop early as lightly laden vehicles pulled far ahead of heavily loaded trucks. Accordion-like, the line stretched.
The convoy had been on the road less than 45 minutes when the 11th ACR’s tactical operational center, received an intelligence message indicating the presence of the headquarters of the VC 274th Regiment 15 kilometers west of Xuan Loc, along Highway 1 near Ap Hung Nghia. The S-2 intelligence officer radioed a warning of the VC location to the 1st Squadron's operations center at Long Binh. At the same time the assistant operations officer, ordered the 11th ACR light fire team (two armed UH-1 helicopters) aloft to cover the convoy. Keltner's ACAV in the second group of escort vehicles was within 1000 meters of the ambush site when his radio crackled with a message from 1st Squadron headquarters warning of suspected VC activity. Keltner had received similar messages before and each time the VC had failed to show up. He immediately radioed the FAC to verify the location of the front of the column and the relation of the lead vehicles to the suspected VC position. Two FACs were by this time circling overhead as one had arrived to relieve the other. Both already were alert to the possible VC activity, having received a coded message two minutes before Keltner. The FACs reported that the head of the convoy, had just passed the suspected VC location. Keltner quickly radioed his ACAVs to warn them of the imminent danger. All but the lead ACAV, C22, answered. A few seconds later at 10:25 C22 reported receiving fire from small arms and automatic weapons and asked permission to return fire. Even as Keltner gave the permission, his own vehicle came alongside the edge of the banana grove that lay south of the highway, and Keltner informed squadron headquarters that the convoy was under fire.
Reacting to earlier counterambush training, Keltner decided to run the column through the small arms fire. From the report of the lead ACAV he believed that the fire was only a harassing tactic, or at the most that it came from only a platoon or a company of VC. In any case, with 80 vehicles to protect and only nine ACAV's to do the job, Keltner felt he had little choice. Still on the move, he ordered his own crew to spray the banana trees south of the road with fire. Just as his machine guns opened up, a mortar round burst close behind his ACAV and immediately in front of the next, A34, but did no damage. While all the ACAV's of the first two groups poured machine gun fire into both sides of the road, nearly half of the convoy, including Keltner's own vehicle, passed safely through and beyond the killing zone. But the full force of the VC ambush still had not been brought to bear. Even though Keltner had received the warning too late to stop the column short of the killing zone, he had been able to alert his escorts almost at the exact moment the VC moved to spring their ambush. The Dong Nai Regiment had been denied the benefit of total surprise.
At Long Binh Lieutenant colonel Martin Howell, the squadron commander, heard Keltner report small arms fire. Like Keltner, he believed it to be harassing fire but nevertheless dispatched the remainder of Troop C to the scene. With Troop C moving out of the staging area and the light fire team helicopters, alerted earlier, rushing to the scene, help was on the way even before the battle reached a peak. Although most of the front half of the convoy had passed out of danger, eight trucks had fallen behind because the first of the eight was carrying a heavy load. As these last trucks and the section led by the next two ACAVs, C18 and C13, entered the killing zone, the ACAVs fired first into the edge of the jungle and, as they kept moving, into the banana grove. The VC answered with small arms and automatic weapons from both sides of the road. To many of the men in the following trucks, this fusillade was the first warning of an ambush, for vehicle noises had drowned out the earlier exchange. The trucks not yet under fire began to slow down, their drivers displaying the uncertainty they felt about what lay ahead. Yet the convoy kept moving and the road ahead remained clear. The exchange of fire grew in volume as those trucks with "shotgun" riders began to engage the ambushers on the right (south) side of the road. Then a round from a recoilless rifle struck C18 on the edge of the loading ramp but failed to stop the ACAV. As the firefight continued at close range, the trucks forming the rear of the column, not yet in the killing zone, began to pull over to the side of the road. Those immediately behind C18 and C13, already under fire, stopped and the men aboard raced for cover in ditches on either side of the road. The only vehicles moving at that point were the last eight trucks from the first half of the column and ACAV's C13 and C18.
Hardly had C18 escaped one round from a recoilless rifle when another burned a hole in its right side, starting a fire. This hit wounded the ACAV commander, but the crew continued to fire the .50-caliber machine gun and the M60s into the VC position south of the road. Now another recoilless rifle round struck the heavily loaded lead truck whose slowness had opened a gap in the truck column. The gasoline tank exploded, instantly killing the two men in the cab. The truck lurched to the left into the ditch on the north side of the road, its trailer still on the pavement, partially blocking the highway. A column of thick black smoke shot into the morning sky. While the crew of C18 continued to fire, the wounded commander radioed his situation to Keltner. After passing the word on to squadron headquarters, Keltner turned around to enter the fight again, but before he could return C18 burst into flames. On orders of the critically wounded sergeant, all the crew except the driver evacuated the vehicle, dragging the sergeant out of the commander's hatch and carrying him into the high grass on the north side of the highway. Only light fire had come from that direction, and it seemed the safest place to go. The driver of the burning C18 finally got it started again and headed down the road through a hail of small arms and antitank rocket fire, hoping to distract the VC's attention and allow the other crewmen to make good their escape. He succeeded, but was shot dead 400 meters down the road.