THEY may be on target as their units' best marksmen, but at the U.S. Army Sniper School they may miss the mark.

Potential snipers gleaned from infantry, special operations and other units must shoot expert as a prerequisite for the school, but there's a lot more to being a sniper than firing a weapon. Graduates not only learn to improve their marksmanship skills, they learn to do their work without being detected.

"A sniper, though mostly thought of as a shooter, spends most of his time searching for a target, not shooting," said MSgt. Edwin B. Nelson, the school's top NCO and an instructor.

The sometimes-frustrating five-week course begins in the classroom. Students learn marksmanship basics, ballistics, range estimation, and camouflage and concealment techniques.

They move to the ranges during the following week, firing at targets set at known and unknown distances, estimating and firing at targets 200 to 900 meters away, learning to judge the effects of wind on a bullet's flight and to set the weapon's sights accordingly, and to move undetected.

Students fire the M-24 Sniper Weapon System from the prone position. That position, they quickly realize, is ideal for missions during which they must observe their targets for long periods of time, Nelson said. Students train as two-member teams, with one person firing while the other records the sight setting and the result of each shot.

But snipers can't hit a target if they can't see it, so students learn to look for unnatural colors, shapes, patterns or textures that contrast with the background.

"A sniper must learn to focus his eyes and brain, so that in one sweep of the binoculars his eyes are attracted to one place," Nelson explained.

To help students, their eyes are tested in target detection exercises that force them to identify objects partially hidden within a given area of terrain.

"We emphasize that we look for something with straight lines; Mother Nature doesn't create anything completely straight," said student Cpl. Jesse L. Benes, from the 2nd Battalion, 7th Infantry Regiment, 24th Inf. Division, at Fort Stewart, Ga.

Avoiding becoming a target is just as important as identifying a target, so students also learn concealment techniques.

Students must make a "Ghillie suit" from BDUs reinforced with canvas in the front and netting sewn onto the back. They thread terrain-colored burlap strips through the netting and add such local vegetation as leaves and branches to help them blend into their environment.

They then test their suits and their stealth in a stalking exercise. The would-be snipers must move 500 to 600 meters toward a target and fire two shots without being detected by an instructor.

"You've got to be very patient and move slow, like a snake," Benes said of the exercise.

PFC Sean McCrossan was spotted after his first shot because the vegetation in his hat had wilted. "I should have stopped and gotten more camouflage," said the 82nd Airborne Div. soldier.

"I've learned to be patient and take the time to get the right shot," said McCrossan.

That, said Nelson, is the mark of a good sniper.