Khe Sanh Combat Base sat on a plateau in northwest Quảng Trị province, eleven kilometres from Laos, at the end of a road that had been cut by ambush since August 1967. Whatever the six thousand men there needed had to arrive by air.

From 21 January 1968 they needed a great deal, because two North Vietnamese divisions were dug in around them and two more sat across the road. Colonel David Lownds initially estimated sixty tons a day. Once five battalions were inside the wire it was 185.

The runway was three thousand feet of aluminium matting laid over crushed rock, described in one account as barely long enough for safe C-130 operations, and it was under artillery observation.

The day landings stopped

On 10 February a Marine KC-130F carrying fuel bladders was hit on approach. It got down, and then burned out on the runway. The pilot escaped through his cockpit window. The following day another C-130 reached Da Nang with 242 holes in it.

General William Momyer ordered USAF C-130 landings to stop. His reasoning was blunt and, from a theatre commander’s perspective, correct: the C-130 was a national resource, and Khe Sanh was chewing them up. Between 12 February and the end of March, USAF Hercules landed there on four days.

Which left a problem. Six thousand men still needed 185 tons a day, and the aircraft best able to carry it was no longer allowed to stop.

Delivering without landing

Three techniques answered it, and they are the reason this siege belongs in aviation history rather than just military history.

LAPES, the Low Altitude Parachute Extraction System, is the one everybody remembers. The Hercules flies down the runway axis at around 130 to 140 knots at a height of five feet. A drogue chute is deployed, restrained to 48 inches, then fired open to its full 28 feet. It rips the pallet off the ramp, and the aircraft flies out from underneath the load while it is still leaving. The pallet skids to a stop, usually within 750 feet.

GPES, the Ground Proximity Extraction System, was the neater idea. A boom and hook on the pallet snags an arresting cable stretched across the runway, and the cable pulls the load out. First used on 30 March, it delivered fifteen loads, mostly construction material, and crews judged it better than LAPES.

Neither of those, though, was the workhorse. That was the Container Delivery System: A-22 containers of about a ton each, fourteen to sixteen per aircraft, released at six hundred feet with a nose-up pull to throw them clear. Ground-controlled approach radar positioned the aircraft and, in overcast, the navigator timed the run. The drop zone was a three-hundred-yard square a thousand yards beyond the runway, which had to be abandoned to the enemy every night and swept for mines every morning.

Worth correcting a myth that circulates widely: you will often read that LAPES delivered 65 per cent of the supplies. It did not. That figure refers to paradrop generally, which was overwhelmingly CDS. Fifty-two LAPES missions were flown in total across the entire siege.

The C-123 Providers and occasional C-7 Caribous kept landing throughout, because passengers, casualties and medical supplies cannot be dropped from six hundred feet.

Contemporary US military footage of the airlift, including extraction drops onto the strip.

The Super Gaggle

The hilltop outposts around the base could only be supplied by helicopter, and helicopters flying predictable routes into fixed positions surrounded by anti-aircraft guns is a formula for losing helicopters. The Marines lost thirty-five during the battle.

The answer, from late February, was the Super Gaggle: twelve A-4 Skyhawks suppressing flak positions and laying smoke while twelve to sixteen CH-46s and CH-53s went into all the hill positions simultaneously rather than one at a time. Marine helicopters delivered 465 tons in February and were running at around forty tons a day by March. According to one Marine officer present, no aircraft was lost during a Super Gaggle.

Il costo

The worst single loss was not a transport shot down over the base but one that never reached it. On 6 March a C-123K of the 311th Air Commando Squadron broke off a landing attempt, was hit by ground fire about eight kilometres east, and spiralled in. Everybody aboard was killed. Sources give 48 or 49 dead; the fuller breakdown is 44 Marine passengers and 5 crew.

Two more C-123s were destroyed on the ground by shelling without fatalities. Fatalities in the 10 February KC-130 are variously reported as six, seven or eight. No USAF C-130 was lost at Khe Sanh during the siege, which given 273 landings and hundreds of drops is a remarkable statistic.

The airdrops killed people too, which is rarely mentioned. A premature LAPES extraction on 21 February killed a Marine. A runaway pallet went into a bunker in mid-March and killed another. A container delivery load came down inside the base and killed five.

Niagara

Around the airlift ran Operation Niagara, the supporting air campaign, launched on 21 January. It averaged something like 350 tactical fighter-bomber sorties, 60 B-52s and 30 observation aircraft a day. By mid-April roughly 100,000 tons of bombs had been dropped around the base.

The Arc Light bomb line, the minimum distance from friendly positions at which B-52s were permitted to drop, was progressively cut as the siege tightened, from around three thousand metres down to one thousand. That is a B-52 cell releasing from thirty thousand feet with a Marine perimeter a kilometre from the impact area.

The campaign also settled a long-running argument. The Marines had always kept their own organic air under Marine control; Westmoreland wanted a single air manager and gave the authority to Momyer. The Marines resisted and Westmoreland reportedly threatened to resign over it. On 7 March 1968, air operations in Vietnam came under a single manager for the first time in the war.

Colour footage of the Marines at Khe Sanh during the siege.

Khe Sanh was abandoned and demolished in July 1968, a few months after it was held at such cost, which is the detail that has made the battle politically contentious ever since. The flying is less ambiguous. Twelve thousand tons were delivered to a runway nobody was allowed to land on, in weather that closed it for days at a time, and the base did not fall.

Air Force footage of the bombing campaign around the base.

Sources: Peter Brush, “Lifeline to Khe Sanh”; Sam McGowan, “Operation Niagara: Airlifters to the Rescue”, Vietnam, February 1993; R. D. Camp, Naval History, February 2004; Bernard Nalty and Ray Bowers, official USAF histories; Prados and Stubbe, Valley of Decision.