As coalition forces fight the Iraqi military, they're also battling another enemy: fatigue.

"Yesterday I finally got a little bit of sleep," said one soldier. "The three days with only three or four hours sleep was pretty rough."

And there's no Starbucks in the middle of the Iraqi desert to provide a java jolt.

The initial ground assault and push toward Baghdad was so fast, allied soldiers went several days with no sleep. And since many have been averaging less than four hours a day, some are worried about a drop in performance.

"It's judgment, situational awareness, ability to anticipate and plan," said Col. Greg Belenky, an Army medical doctor. "These things are sensitive to sleep deprivation."

Belenky, the army's leading sleep scientist, is developing a wrist monitor that logs sleep and can alert a soldier who is getting dangerously drowsy. But right now, it's up to battlefield commanders to manage troops' sleep just as they would other essentials such as food and water.

"It's very difficult to effectively manage because commanders are in a situation where they actually don't know how much people are sleeping, and it's difficult even on the scene to get a good idea," Belenky said.

To combat fatigue, the Army includes caffeine in daily rations, and the Air Force offers pilots Dexedrine, or "go pills."

The pills are basically amphetamines, known on the street as "uppers" or "speed," so the military carefully monitors their use. They're used in the military to stay awake on long combat missions.

But all these countermeasures are only a temporary fix, and the pills may have some bad side-effects.

Two U.S. Air National Guard pilots were charged last fall with involuntary manslaughter in a friendly-fire incident over Kandahar, Afghanistan, on April 17 that resulted in the deaths of four Canadian soldiers and the wounding of eight others. The pilots were given amphetamines -- the "go pills" -- for their mission.

Now they could face 64 years in prison for mistakenly dropping a bomb on the Canadians when they saw weapons fire, although a military hearing officer who was presiding over a hearing in Louisiana in January has recommended against court-martialing the pair.

Col. Patrick Rosenow said that although there was enough evidence to court-martial the two, internal Air Force penalties would maintain "the interests of good order and discipline."

Canada and critics say the two were too quick to open fire under rules of engagement, which some experts say can happen if someone is taking amphetamines.

According to their defense lawyers, the pilots were told by their superiors in Kuwait that they could be found unfit to fly their mission unless they took the pills. Military officials, on the other hand, describe the pills as a "medical tool" that is prescribed only in small, controlled doses.

"This is speed. This is where we got the phrase, speed kills," Robert DuPont, a former White House drug czar, told ABC News in December, when preliminary court proceedings began against the two pilots.

It's because of the need for sleep that experts viewed the sandstorms that slowed the forward push by coalition forces last week as a blessing in disguise -- a rare chance for the soldiers to steal a few extra Zs.

Superior night vision and related technology gives the U.S. military a significant advantage, but also stretches the length of the combat day, requiring troops to perform more complex jobs on less sleep than ever before.

"I don't know of a substitute for sleep, except sleep," said Dr. Carol Landis, a sleep researcher at the University of Washington. "When you haven't had sufficient sleep, what you need is a good night's sleep."

Fox News' Liza Porteus contributed to this report.