IN THE IRAQI DESERT -- It's not easy napping in a Humvee rumbling across the Iraqi desert. Or in a shallow, single-soldier trench. Or stretched out on chilly sand. Still, exhausted U.S. soldiers are adapting to sleeping on the move.

As the 101st Airborne Division sprints deeper into Iraq, troops catch shut-eye when they can. Friday night was spent in dusty trenches dug into the Kuwaiti desert, each one just wide enough, long enough and deep enough to hold a single soldier.

Some tried to nap Saturday as the convoy trekked north.

Staff Sgt. Michael Vaughn eagerly stretched his aching limbs during a break in the marathon roadtrip. He'd managed to doze in the passenger seat of a truck for several hours, wedged between ammunition, rucksacks and bottled water.

The soldiers have driven almost ceaselessly since tearing across the border from Kuwait on Friday evening, a day behind the first U.S. and British troops into Iraq. They stop about every four hours for rest breaks.

Sleeping in heavy combat helmets -- required in the battle zone -- and behind goggles that protect against the relentless desert dust would be hard enough for most. But a solid rest seems even more elusive amid the roar of trucks, the clatter of gear and the tight quarters.

Units across the front are facing similar sleep deprivation.

Members of the 18th Military Police Brigade slept in Humvees and Army trucks, on cots or in sleeping bags tossed on the sand alongside the vehicles. A light rain chased some inside, or even underneath the bulky personnel carriers, but some exhausted soldiers simply turned their faces and slept in the rain, despite the constant drone of equipment and blast of headlights.

Marines of a heavy helicopter squadron near Iraq fly day and night across the desert delivering equipment, fuel and ammunition to ground troops. Under threat of missile attack, those at the secret camp are continually sent to their bunkers by warnings, and they get little unbroken sleep.

Those who seem to have it worst of all are the infantry; those with the 101st Airborne sleep in the back of open trucks, up to 16 packed in cheek by jowl, resting with their gear hanging nearby. Some get up during the night and eat in the cabs of Humvees -- beef ravioli and shrimp jambalaya.

Constant worries about chemical weapons also keep everyone on alert.

Marines with the 1st Platoon, Echo company mechanized infantry, sleep under the stars in the chilly desert, as explosions are heard in the distance. They must rise regularly to don gas masks.

As uncomfortable as it is, the ones that do get to sleep are the lucky ones.

Pvt. Andrew Herzog, 19, of the 101st Airborne, spent a night standing on top of his Humvee, an MK-19 grenade launcher at the ready, wearing goggles and scarf to brace against the 40-degree temperatures, howling winds and dust.

"It's not too bad," said Herzog, of Camden, Mich., snacking on peanut butter, crackers and water.