Most nerveracking of all, and the source of most deaths, was the task of penetrating the trap doors that led from level to level, usually downward.

Often a tunnel would come to a dead end. Or was it a dead end? If so, why dig it in the first place? In the dark, with fingertips feeling nothing ahead but laterite wall, no side tunnel to left or right, the Tunnel Rat had to use his flashlight. This would usually reveal, skillfully camouflaged and easily missable, a trap door in the wall, floor, or ceiling. Either the mission was aborted, or the door had to be opened.

But who waited on the other side? If the GI's head went through first and there was a Vietcong waiting, the American's life would end with a throat cut from side to side or the lethal bite of a garroting noose of thin wire. If he dropped downward feet first, it could be the spear through the belly. Then he would die in agony, his screaming torso in one level, ruined lower body in the next one down.

Dexter had the armourers prepare him small, tangerine-sized grenades with a reduced explosive charge from the standard issue but with more ball bearings. Twice in his first six months he lifted a trap door, tossed in a grenade with a three-second fuse and pulled the door back down. When he opened the trap door a second time and went through with his flashlight on, the next chamber was a charnel house of torn bodies.

The complexes were protected from gas attack by water traps. The crawling Tunnel Rat would find a pool of rank water in front of him. That meant the tunnel continued on the other side of the water.

The only way through was to roll onto one's back, slide in upside down, and pull your body along with your fingertips scrabbling at the roof. The hope was that the water ended before the breath in your lungs did. Otherwise, the Tunnel Rat could die fifty feet under, drowned, upside down, in blackness. The way to survive was to rely on a partner.

Before entering the water, the point man would tie a lanyard to his feet and pass it back to his partner. If he did not give a Dext reassuring tug on it within ninety seconds of entering the water confirming that he had found air on the other side of the trap, his buddy had to pull him back without delay because he would be dying down there.

Through all this misery, discomfort, and fear, there occurred a moment now and again when the Tunnel Rats hit the motherlode. This would be a cavern, sometimes recently vacated in a hurry, which had clearly been an important subheadquarters. Then boxes of papers, evidence, clues, maps, and other mementoes would be ferried back to the waiting Intelligence experts from G2.

Twice the Badger and the Mole came across such AladdinÕs caves. Senior brass, unsure how to cope with such strange men, handed out medals and warm words. But the Public Affairs people normally avid to tell the world how well the war was going, were warned off. No one mentioned a word. One facility trip was arranged, but the "guest" from PA got fifteen yards down a "safe" tunnel and had hysterics. After that, silence reigned.

But there were long periods of no combat for the Rats as for all the other GIs in Vietnam. Some slept the hours away, or wrote letters, longing for the end of their tour and the journey home. Some drank the time away or played cards or craps. Many smoked, and not always Marlboros. Some became addicts. Others read.

Cal Dexter was one of those. Talking with his officer partner he realised how blighted his formal education was and started again from square one. He found he was fascinated by history. The base librarian was delighted and impressed, and prepared a long list of must-read books, which he then obtained from Saigon.

Dexter worked his way through Attic Greece and Ancient Rome, learned of Alexander, who had wept that, at thirtyone, he had defeated the known world and there were no more worlds to conquer.

He learned of Rome 's decline and fall, of the Dark Ages, mediaeval Europe, the Renaissance, and the Enlightenment, the Age of Elegance and the Age of Reason. He was particularly fascinated by the early years of the birth of the American colonies, the Revolution, and why his own country had had a vicious civil war just ninety years before he was born.

He did one other thing in those long periods when monsoons or orders kept him confined to base. With the help of the elderly Vietnamese who swept and cleaned the "hootch" for them all, he learned workaday Vietnamese until he could speak enough to make himself understood and understand more than that.

Nine months into his first tour, two things happened. He took his first combat wound, and the Badger ended his twelve-month stint.

The bullet came from a VC who had been hiding in one of the tunnels as Dexter came down the entrance shaft. To confuse such a waiting enemy, Dexter had developed a technique. He threw a grenade down the shaft, then went in fast, hand over fist. If the grenade did not blow away the false floor of the shaft, then there was no punjistick trap down there. If it did, he had time to stop before he hit the spikes.

The same grenade ought to shred any VC waiting out of sight. On this occasion, the VC was there but standing well down the passage with a Kalashnikov AK-47. He survived the blast but was injured and fired one shot at the fast-falling Tunnel Rat. Dexter hit the deck with his pistol out and fired back three times. The VC went down, crawled away, but was found later, dead. Dexter was nicked in the upper left arm, a flesh wound that healed well but kept him above ground for a month. The Badger's problem was more serious.

Soldiers will admit it, policemen will confirm it; there is no substitute for a partner you can utterly rely on. Since they had formed their partnership in the early days, the Badger and the Mole did not really want to go into the tunnels with anyone else. In nine months, Dexter had seen four Rats killed down there. In one case, the surviving Tunnel Rat had come back to the surface screaming and crying. He would never go down a tunnel again, even after weeks with the psychiatrists.

But the body of the one who never made it was still down there. The Badger and the Mole went in with ropes to find the man and drag him out to be sent home for a Christian burial. His throat had been cut. No open casket for him.

Of the original thirteen, four more had quit at the end of their time. Eight down. Six recruits had joined. They were back to eleven in the whole unit.

"I don't want to go down there with anyone else," Dexter told his partner when the Badger came to visit him in the base clinic.

"Nor me if it were the other way around," said the Badger. They settled it by agreeing that if the Badger extended for a second oneyear tour, the Mole would do the same in three months. So it was done. Both accepted a second tour and went back to the tunnels. The division's commanding general, embarrassed by his own gratitude, handed out two more medals.

There were certain rules down in those tunnels that were never broken. One was: Never go down alone. Because of his remarkable hazard antennae, the Mole was usually up at point with the Badger several yards behind. Another rule was: Never fire off all six shots at once. It tells the VC you are now out of ammo and a sitting duck. Two months into his second tour, in May 1970, Cal Dexter nearly broke them both and was lucky to survive.

The pair had entered a newly discovered shaft up in the Ho Bo Woods. The Mole was up front and had crawled three hundred yards along a tunnel that changed direction four times. He had fingertip felt two booby traps and disconnected them. He failed to notice that the Badger had confronted his own personal pet hatred, two tomb bats that had fallen into his hair and had stopped, unable to speak or go on.

The Mole was crawling alone when he saw, or thought he saw, the dimmest of glows coming from around the next corner. It was so dim he thought his retina might be playing tricks. He slithered silently to the corner and stopped, pistol in his right hand. The glow also stayed motionless, just around the corner.