Vietnam Airmobile Warfare Tactics

Helicopters were relatively slow, lightly armored and fragile. Many felt that they would be highly vulnerable to light antiaircraft and small arms fire. The nature of their operations often required them to fly low, and they would have to land in enemy–controlled territory to deliver troops and supplies; this obviously increased their vulnerability, and it was widely anticipated that losses would be high.

Some 12,000 helicopters of all services were sent to Vietnam; from 1961 to 1971, the US forces lost 2,066 helicopters to enemy action, and another 2,566 to operational accidents, mishaps and weather. More than 22,000 helicopters were hit, many of them more than once. This might be considered high — but the context was more than 36 million sorties flown during this period.

Most of the weather mishaps were due to heavy rain, fog or low cloud when visual contact with the ground was lost. Most helicopters were equipped to fly with instrument flight rules (IFR), but few airfields were equipped with instrument approach systems. The major problem was that pilots had little experience with IFR even though they were rated with either a Standard or Tactical Instrument Ticket. To maintain IFR proficiency required a great deal of time, which was not available, and was extremely difficult. Additionally, there were usually insufficient on-board fuel reserves to fly IFR.

In order to maximize helicopter lift capacity and maneuverability the machines could only be provided with limited armor. Only pilots were provided with armored seats, offering protection from below, the rear, and (partially) from the outboard sides. The engine compressor was partly protected by armor, but the highly vulnerable tail rotor gearboxes and transmission were not. Fire extinguishers were carried, but there was no engine compartment fire suppression system, merely infrared fire detectors to set off warning lights. All crewmen wore body armor vests, and the aviator's helmet offered some ballistic protection. Vests were provided with add–on front and back "chicken plates," but the back plate was often discarded. Fire–resistant flight suits and gloves were used, and canvas–topped jungle boots were given up for all–leather boots offering better fire protection. Gunners would sometimes sit on spare armor vests or scrounged armor plate, but most enemy fire came from the sides.

The safest altitudes to fly were either very low or very high. High speed, treetop–level flight (below 100 feet) made it extremely difficult for a gunner on the ground to hit a helicopter. It was hard to determine the exact direction it was coming from, and the noise was not heard as early as when it was flying higher; the aircraft came over so fast and low that it was only exposed for seconds. Another method was "nape–of–the earth" flight; this technique entailed the helicopter flying over and among trees and terrain features, using them as cover and constantly varying altitude and speed. From beneath double–canopy forests and rubber trees it was virtually impossible to see a helicopter, or for it to see the ground. To avoid antiaircraft fire a safe altitude was 1,000ק,500ft, and high altitude flight also improved radio range.

The most vulnerable time for a helicopter was when it was transiting from forward flight to ground–effect just as it was landing. It was moving forward very slowly at this point, and would require valuable moments to transition to take–off. Of course, hovering just above or actually sitting on the ground made it a stationary target, even though it would only take seconds to off–load its troops. A helicopter taking off under fire was also in serious danger, since it was low, the speed could only build up gradually, and the pilot could not take evasive maneuvers because of other helicopters on and around the LZ, and had to avoid trees. Attack helicopters were vulnerable when making their run on the target, since the enemy knew that they had to fly on a straight course in a shallow dive.

To reduce enemy fire on potentially hot LZs, these would be generously "prepped" by artillery followed by gunships. The lift helicopters would suppress the treeline with their machine guns, before off–loading and departing in seconds. A significant problem was simply that unless aircrews detected muzzle flashes or tracers, or felt the impact of hits, they did not know they were under fire. Sometimes other aircraft notified them, and experimental gunfire detectors were installed on a few aircraft; but for the most part crews did not know they were taking fire until they heard disturbing noises actually in the fabric of their helicopters.