BBC News, Vietnam
This From Our Own Correspondent was first broadcast on 23 May, 1970.
Driven by Cold War concerns over the spread of communism, the US sent troops to South Vietnam in 1954. By 1970, 400,000 soldiers were stationed there. In Vietnam, Anthony Lawrence discovered what life was like for the US soldiers on the front line.
Soldiers' morale is difficult to analyse, especially here in Vietnam.
Wars are different now.
The old vocabulary - words like "bravery", "discipline", "morale" - does not meet the problem.
In the Vietnam War you mostly do not need brave men, you need efficient ones able to handle highly-sophisticated instruments of transport and death.
And the standard length of service in Vietnam is one year.
For most of the 400,000 Americans still out here, the best morale builder of all is that you can actually count the days to going home.
But there are tremendous contrasts.
Many of the soldiers have an easy time, with their nightly cinemas, good food and modern plumbing.
There are about 80,000 men, less than a fifth of the total US army in Vietnam, who really meet the enemy close-up: killing and getting killed
Many are better off than they would be in the States.
But when you leave the big bases and maintenance areas and get out into the wilds, then it is different.
There you meet the real soldiers: the men of the infantry, and the air cavalry units.
There are about 80,000 men, less than a fifth of the total US army in Vietnam, who really meet the enemy close-up: killing and getting killed.
They are young, mostly drafted men, graduates, college dropouts, a large proportion of negroes. Their nickname is "grunts", from the way the soldier grunts as he shoulders his heavy pack.
They spend most of their time out in the wild forest near the frontiers, where the enemy is always infiltrating.
You can go for months and meet nothing, and then three times in one week you meet some awful ambush or firelight
They may be out for as long as a whole month at a time. And when they return it is not to a camp with cinema shows and hot showers, but to a so-called fire-base with gun-pits and holes in the ground to sleep in.
And their chance of getting killed or wounded is very high.
That is the sector where morale is under pressure.
It is such a chancy business, this patrolling.
You can go for months and meet nothing, and then three times in one week you meet some awful ambush or firelight.
The man next to you goes down yelling with a leg blown off. The platoon commander is bleeding to death against a tree.
It is over in 15 minutes, but it is a nightmare. And it may come again tomorrow night.
In this infantryman's life, the great thing is to come safe home, 'to keep your arse covered', as the soldiers call it
When you get back from all that, the re-enlistment sergeant is waiting for a little chat.
He can get you out of all that, he says, if you are ready to sign on for a longer spell in the army, get you a cushier job.
In this infantryman's life, the great thing is to come safe home, "to keep your arse covered", as the soldiers call it.
There is a vast gap between, on the one side, the junior officers, NCOs and men, and on the other, the higher ranks, the career officers, the so-called "lifers".
It is the "lifers" who believe in conventional discipline.
But the men who stay out in the forests, beating the bush, as they call it, they are all, including lieutenants, on Christian name terms and there is no formality, except that everyone does what he has to do.
It is the case of old soldiers doing what cannot be got out of, doing their duty
"I never thought about morale," said one young lieutenant. "The life certainly changes you a lot.
"Luxury, to me, is staying in a forest clearing for one whole afternoon without having to move on. A drink from a cold stream's a gift from heaven. A bed to sleep on, unimaginable."
What about pot-smoking?
Platoon commanders confirmed to me that a lot goes on. But there would be big trouble if some idiot smoked just before going on patrol.
It brings on enormous thirst and for a while dulls perception, which is fatal.
Most of the young men I spoke to thought the army was badly run and the war a great mess.
Their only respect is for each other and for the enemy who kills and dies like they do, along the forest trails
But that is not bad morale. They would not run away.
It is the case of old soldiers doing what cannot be got out of, doing their duty.
And again, in the old tradition, their main contempt is for the overweight sergeants back at the base, the generals' talk of kill ratios.
Their only respect is for each other and for the enemy who kills and dies like they do, along the forest trails.
And they know, too, that when they get back to the States, there is no one to talk to about what they have been through. No one who wants to listen.