NORTHERN KUWAIT -- "Gas, gas, gas!" comes the muffled cry as Iraqi shells explode in the distance.

Instantly, everyone rips open the gas mask holders on their hips and pulls out the masks. They have nine seconds, if the gas is a nerve agent, to put on the mask, blow hard to clear it and check the seal.

Thankfully, it was a false alarm on Thursday -- one of many prompted by Iraqi missile attacks. Most of the Marines of the 1st Platoon, Echo company of the 15th Marine Expeditionary Force appear to make the deadline.

Gas, whether biological, chemical or nerve agent, is one of the greatest worries of these Marines and other troops ready for action in Iraq. And this is not a drill. Iraqi shells have exploded within distant earshot, and gas masks donned just in case.

When the troops head into Iraq across the "berm" -- long, manmade sand dunes -- they will wear protective suits and have gas masks handy as a precaution. They go everywhere with their masks, sometimes sleeping with them as pillows or strapped to their arms should an alarm come during the night.

'Pools of sweat'

The suits look and feel like heavy camouflage field uniforms, and are lined with charcoal filters to keep harmful agents from seeping through. But that also makes them airtight, so they are hot and trap sweat inside, a particular hardship in the soaring heat of the harsh desert.

"I can't even begin to tell you how hot," says Sgt. Robert Renfrow, 28, of Lake Stevens, Wash. "Your hands will swim in pools of sweat."

In fact, the new chemical and biological suits are seen by the Marines as a huge improvement over the ones they used as recently as two years ago. That version was even hotter, and left their clothes and bodies covered with charcoal.

The suits are officially called Chemical Protective Outer Garments -- in military speak, CPOGs -- while the Marines universally call them MOPP suits, from the levels of preparedness known as Mission Oriented Protective Posture, or MOPP, in use in the field.

The Marines will head into Iraq at MOPP 1, which means they are wearing their protective suits. At MOPP 2, they would add the rubber boots, or overshoes. At MOPP 3, they add rubber gloves, and finally at MOPP 4, put on their gas masks.

Wearing what amounts to a sauna suit and mask, and then adding a flak jacket, weapons harness and about 60 pounds of gear and weapons can be a terrible ordeal.

Sgt. Jeff Seabaugh, 23, of Colorado Springs, Colo., once had to wear a MOPP suit for 48 hours straight and calls it "absolutely miserable."

Lance Cpl. Spencer Hale, 23, of Tupelo, Miss., recalls going through a training course in this region when temperatures were up to roughly 125 degrees.

"I thought I was going to die," he says. They had to run seven laps around a warehouse with their suits, masks and full combat gear.

"It was probably the hardest thing I have ever had to do," Hale said. "Not physically, but you couldn't breathe."

It isn't just the soldiers that are coping with the cumbersome masks and suits. Journalists embedded in the military units also must use the gear -- sometimes while writing their stories or doing their live TV shots.

This reporter wrote much of this story wearing a gas mask.

Marines can also become victims of their own vices, such as chewing tobacco, or dip as the troops call it. Slapping on a gas mask with a jaw full of dip leaves nowhere to spit.

"I ended up swallowing a whole dip. It made me feel sick," says Hale.

Even having the mask on for just 45 minutes, as was the case for the troops early Thursday, leaves the face soaked with sweat. If it's hours or days, that leaves the face raw or full of rashes. And while the Marines want their masks tight to keep out gas, straps that are too tight can cause a severe headache.

The gear is tough to wear but also gives an edge because, as Cpl. Juan B. Elenes, 21, or Portland, Ore., says, "We are awfully confident in our gas masks and MOPP suits."

Minutes after the false alarm on Thursday, the shout of "gas, gas, gas" is again heard down the line of armored vehicles and tanks scattered in the desert. The Marines slap on their masks again, and wait.