Khe Sanh was a US Marine firebase in the north-western corner of South Vietnam during that country's vicious civil war. It occupied a strategically important position about ten miles from the Laotian border and 15 miles from the demilitarised zone marking the border with the Communist North. The base and supporting airstrip, with its 7000 defenders, were set within a compound approximately one mile long and half a mile wide. This compound in turn occupied an 800-feet-high plateau in the middle of a valley, which was itself bordered by hills and mountains up to 4000 feet in height.

The base was constructed in 1962 due to the strategic significance of its position astride the 'Ho Chi Minh Trail' supply route into the south. It was hoped that the base could be used as a jumping-off point to destroy the supply convoys of arms to the Communist North Vietnamese Army (NVA). In 1968 the US commander, General Westmoreland, went further and decided to use the base as a lure to force the NVA into a decisive battle. He moved heavy reinforcements into the area in order to conduct major operations to cut the Ho Chi Minh Trail in the area. This move would force the Communists to come to battle, as to cut the trail would deny them of all supplies. He was eventually unable to conduct these offensive operations, since the speedy deployment of the NVA forces quickly hemmed his troops into their compound. It was the build up and disposition of forces in the area, as well as the surrounding geography, that led to the invention of the Khe Sanh Approach.

The Siege

Seeing the way the US troops were disposed, General Giap, the NVA commander, laid siege to the base, obviously hoping to slowly strangle it into submission as he had the French base at Dien Bien Phu in 1954¹. Unfortunately for him, whilst his tactics had worked then, the enemy he was now facing was vastly better equipped and could call up far greater reserves of superior aircraft to supply and defend themselves. The siege began on 21 January, 1968 as Giap's 25,000 men completed their encirclement to prevent the base being resupplied over land. From this point until the siege was broken 77 days later, the base could only be resupplied by air.

The Khe Sanh Approach

The encirclement of the base meant that there was no safe corridor for the transport aircraft to use for their approach. Any descent towards the airstrip attracted heavy fire from enemy weapons, ranging from infantry small arms up to 12.7mm heavy machine guns and larger calibre anti-aircraft cannon. In order to minimise the risks posed by these hazardous conditions, the transport crews perfected the manoeuvre that came to be known as the Khe Sanh Approach.

A standard landing approach towards a runway would consist of a constant, controlled descent at a shallow angle, but the surrounding hills and risk of enemy fire forced the crews to keep their large, comparatively unwieldy craft (Lockheed C-130 Hercules, Fairchild C-123 Provider and De Havilland C-7 Caribou)², at a much higher level for longer in order to stay out of range of small-arms and present a smaller target to the larger-calibre weapons. Then, as the aircraft approached the end of the runway, the pilot would drop the nose and put the aircraft into a steep dive, levelling out only at the very last moment. From here, the pilot could either land or make a very low-level pass along the runway at an altitude of about five feet, dropping the supplies out of the open rear cargo doors along the way. The pilot would then pull up sharply at the far end of the runway and execute a steep climb out of the valley, helped by the fact that the plane was now much lighter, having deposited its load.

Such low-level passes could be facilitated by one of two methods. The first was known as LAPES, or Low Altitude Parachute Extraction System, and worked by streaming parachutes from the back of the plane as it flew down the length of the runway. These parachutes would be attached to cargo pallets on a roller system in the cargo bay. As the parachute deployed, the pallets would be dragged out of the plane and would eventually skid to a halt, allowing the delivery craft to leave its supplies without touching the ground. This allowed the crew to avoid becoming a stationary target on the runway for enemy artillery, a menace that claimed several aircraft over the course of the siege. This method was eventually discontinued, however, as the pallets did not always come to rest as quickly and smoothly as planned, causing accidents and the deaths of several Marines.

The other, safer method was known as GPES, or Ground Proximity Extraction System. This worked on a similar principle to LAPES, but instead of relying on parachutes to drag the pallets from the plane, they were fitted with a hook that attached to a line stretched across the runway. This had the advantage of bringing the pallets to a virtual stop as soon as they hit the ground. Using these and more conventional higher-altitude parachute delivery methods, the transports were able to supply the 7000 man garrison with 12430 tons of supplies in the course of the 77 days – enough to keep the NVA at bay until the siege was finally lifted.

The Khe Sanh Approach Today

The Khe Sanh Approach is still used today in situations where groundfire is potentially a problem. It was used by coalition forces in the Kuwait conflict and by UN forces in the Balkans, (which led to its alternative name, 'The Sarajevo Approach'). The only modification which has been made to the basic manoeuvre is that the aircraft will now jink from side to side on its approach in order to confuse and evade any potential missile threats.

The technique is also a very popular attraction at air displays and is popular with the display crews of many types of large aircraft, not just the ones mentioned above. It is the Hercules that is the most common performer, though, and it flies in the colours of many different nations. Being a prop-driven aircraft it also has a very distinctive sound, reminiscent of an enormous drone bee dawdling across the sky. With its droopy cockpit 'face' and bulky fuselage it looks ponderous. When it drones lethargically towards the end of the runway, as with every large aircraft on final approach, you wonder why it doesn't just fall out of the air. It is probably travelling at a speed that would embarrass most other forms of transport, yet it blocks out a quite unnerving amount of the sky, seems far too big to be held up by something as insubstantial as air and seems to be hardly moving at all.

Then the pilot drops the nose and your stomach suddenly turns over as this bulky aircraft, helped by the alarming impetus of gravity, goes into an indecently steep dive towards the ground. One of the weirdest things about this is the fact that you get to see the upper side of the wing. With planes this big, this rarely happens. If you see them on the ground, you walk under and around them, always looking upwards. When you see them in flight, you obviously very rarely get to see them from any quarter other than below. Seeing the top half of the Hercules like this therefore feels inherently wrong, especially since the plane is pointing directly at the ground. Like seeing a picture of sinking ship perpendicular in the water or a crashed car upside-down with wheels still gently turning, seeing the unfamiliar upper side of the wing induces a sort of subconscious panic.

The drone of the propellers then increases in pitch as the air now rushing past them makes them spin more quickly and the knot in your stomach rises up to your throat as you realise that the plane is surely going to crash... and then, at the very last moment, the pilot levels out, wheels perilously close to the ground, and makes a pass along the runway, dropping parachuted pallets along its length. It is only as it thunders past your position on the flightline that you realise just how fast it is travelling, and how that dull buzz of propellers and engines is actually a roar. If you are close enough, you will feel the backwash pull at you as the huge, imposing mass punches its hole through the air as it passes, sucking anything not nailed down across the runway in its wake. Then it will climb steeply and within seconds it will be a thousand feet up, banking sharply away, and the roar will revert to a distant drone, the pitch dopplered to a lower and more relaxed note.

It's a pretty spectacular turn.