"The Ho Chi Minh trail is a great python feeding on pigs."
-North Vietnamese Army political officer.
The Ho Chi Minh trail was the thing that really thwarted the Americans in the Vietnam War, and strategically the only battle that really mattered.
US military intelligence claimed it knew "all 5645 kilometres of the Trail system", but Vietnamese strategists speaking from Hanoi say it was a road system of 13,000 kilometres. In some places it was little more than a dirt track, in others it was entirely motorable and possible "for two trucks to pass abreast". Why was this road system so important?
NVA and Viet Cong operating in South Vietnam - where they effectively controlled most of the countryside - had a few problems. They needed to get reinforcements and supplies from the North. From 1965 onwards they couldn't get it by the sea, because the South had plugged up this route. The Pentagon believed that the covert war in the South could be sustained with about 60 tonnes of material a day, and this is almost exactly what the North managed to slip down the trail. And how the hell did they manage that against the horror of the Green Berets, bombing and Project Igloo White, not to mention natural threats such as malaria and snake-bite?
The air war on the Trail was to run into a lot of problems. Sorties began to be flown in 1964 (there were roughly 300 a year until 1967 when they began to be tripled), but the value of the B-52 in this situation was in question. It is estimated that in the peak year of movement south, about one in every hundred infiltrator was killed, at an estimated cost of $2 billion dollars (the Americans spent roughly a million dollars a day on artillery shells). Project Igloo White was an attempt to co-ordinate the efforts of the bombers better, and rather than repeat that excellent node I shall only suggest you read it.
The pilots also had to cope with a three-layer jungle canopy which made them literally blind - by 1970 the entire trail was protected by almost a thousand anti-aircraft guns, some of which had radar.
The Vietnamese marching down the trail had to deal with disease and animal attack. But they all carried medicine against malaria and snakebite, and there were actual pharmacies along the trail producing medicine for the troops. There were also barracks placed at regular intervals - a day's march apart where this was possible - which acted as communication centres, logistical centres and re-supply stations for the troops. Animals were kept in farms and vegetable gardens cultivated in these barracks to keep the troops fed.
The North Vietnamese had a fleet of about 25,000 trucks, and the fleet was being pretty much entirely destroyed every year. However, such was economic aid from China and the Soviet Union that they could easily afford to replace them every year. Trucks usually only drove for a few hours every night, and each driver was limited to a small section of the trail, which ensured he knew his territory very well. Supplies would be unloaded and moved into the next set of trucks at a set point on the trail, often a barracks. Special groups of Vietnamese in the barracks - many women - acted as road repair gangs (it is estimated there were between 40,000-50,000 such individuals at any one time) to patch up the damage caused by the bombing.
Back in the US, people wanted to know why the military simply couldn't "plug up" the Ho Chi Minh Trail. It simply wasn't this easy. For a start, the Trail was in fact thousands of trails, and it passed through some of the most inhospitable regions of the country - areas the French had made "no effort to control" because they were "remote, isolated and undeveloped" (quotes from a Laotion military commander). Air operations against it were limited by poor intelligence. A billion-dollar plan to build a "fence" - a massive minefield with barbed wire and thousands of acoustic and seismic sensors was discounted. And then there was the problem of Laos.
The 1962 Geneva Accord had neutralized Laos. Neither the Americans nor the North Vietnamese were allowed to conduct ground operations there. But the Ho Chi Minh Trail travelled right through Laos, and tens of thousands of Northern troops infiltrated across the Laotian border monthly. General William Westmoreland and American Ambassador to Saigon Ellsworth Bunker wanted to cut into Laos right up to the trail and hold it, effectively "withering the Viet Cong on the vine" - and they wanted 60,000 troops to do it. The North had violated the Geneva Accord from the moment they'd signed it, and fears of escalation if the war spread (it was thought China may intervene as they did in Korea) were dismissed by saying that neutral France and Britain could explain to the Chinese that America had no designs on China or even North Vietnam, but that the North could not be allowed to take the South. But, skeptical, President Johnson forbade all talk of invading Laos.
The Royal Lao Air Force - which had American sympathies - flew sorties against the trail, and American-indoctrinated Asians conducted covert operations, often acting to direct the actions of the air force against lucrative targets (troops that do this are called Forward Air Controllers). This was called Operation 35, and although it had a modest financial cost the human cost was greater, as it often is with black ops.
At the end of the day, 60 tonnes isn't a lot. That's about 15 trucks - and I'd like to see the air force that could stop even all but 15. So long as it was fighting for me.