100 monkeys typing.

Wings.

It is a weariness that has created its own culture of superstition. There are vehicle commanders who will not let the infantrymen in the back fall asleep on long operations - not because they want the men alert, but because, they say, bad things happen when people fall asleep. So the soldiers drink multiple cans of Rip It and Red Bull to stay alert and wired.

But the exhaustion of the US army emerges most powerfully in the details of these soldiers' frayed and worn-out lives. Everywhere you go you hear the same complaints: soldiers talk about divorces, or problems with the girlfriends that they don't see, or about the children who have been born and who are growing up largely without them.

'I counted it the other day,' says a major whose partner is also a soldier. 'We have been married for five years. We added up the days. Because of Iraq and Afghanistan we have been together for just seven months. Seven months ... We are in a bad place. I don't know whether this marriage can survive it.'