FORT IRWIN, Calif. -- Business is normal on your forward operating base in the middle of the desert, until suddenly you hear rounds popping in the distance and colliding with the ground.

Your world begins to shake.

Within minutes, ambulatory Stryker vehicles are rushing casualties to your aid station as silence turns to screams and Soldiers who were once walking and smiling are now sprinting and shouting.

Everywhere, medics are jotting down vitals, hooking up intravenous fluids and franticly tearing open gauze packets. Some wounded are missing limbs; some are violently calling the medics idiots, pleading desperately for their comrades.

"Captain Stone was just here!" one of them yells, lying on an operating table.

A chaplain -- a tiny Bible in hand -- kneels down beside a Soldier on a stretcher and bows his head. Together, they recite a prayer.

It's mass confusion; it's chaos.

Welcome to the National Training Center.

Here, the situation can change at a moment's notice and the craziness can escalate in the blink of an eye, but for medics and other Soldiers with the 702nd Brigade Support Battalion on FOB Denver -- a mock southern Afghanistan base -- chaos is welcomed with well-rehearsed performance.

Soldiers with the battalion harnessed their A game June 12 when a normal day turned into a mass casualty exercise with injured role players designed to test the entire FOB, but especially medics with the battalion's medical company.

The test served as just part of nearly an entire month of training the battalion is undergoing with the rest of its parent unit, the 4th Stryker Brigade Combat Team, 2nd Infantry Division, in preparation for a deployment to Afghanistan this fall.

"It allows our medics to be exposed to crisis management, and to have a lot of personnel coming into an aid station at one time to really cause a lot of chaos for them," said Command Sgt. Maj. Anthony Fourtunia, a New Orleans native and the battalion's commander. "When you have role players come in, it makes it really realistic for them and gets that adrenaline flowing."

For the battalion's company of medics, Company C, the mission was to take in casualties from two separate battalion aid stations on the base that serve as the first level of medical care for their Soldiers.

Company C operated as a second-level treatment facility, and cared for and evacuated approximately 35 wounded via Strykers and helicopters to more permanent care.

With so many moving pieces, chaos ultimately prevailed, even for the most seasoned medics on ground. But often times even the most intense pressure and stress can solidify confidence.

"If the Soldiers knows what their capabilities are before they go downrange, it builds their confidence," he said. "And for every warrior who goes downrange, if they don't have confidence performing their duties, it would be pretty hard for them to execute their mission."

Eight-year medic Sgt. Brenda Porto knows from experience that the sentiment is true for any medic.

"We get these scenarios in real life, so they need to be able to understand how to handle the stressors while we're here and cope with them," said Porto, a Las Vegas native and a C Co. medic. "And if they learn how to do that here, it'll be better once overseas.

"Any sort of experience -- once you sort of know what to expect -- it keeps you cool and calm. You won't freak out as much."

The company's first sergeant, 1st Sgt. Kristopher Rick, said his Soldiers have rehearsed similar exercises at their home station, Joint Base Lewis-McChord, Wash., and twice at Yakima Training Center in Central Washington State.

But while the unit was well versed on what to expect, it hasn't yet rehearsed a mass casualty to such a large scale.

"It is very, very rare to have the opportunity to rehearse that at a FOB level that has more than one tenant unit," said Rick, a Yuma, Ariz., native. "You don't usually get to experience that until you get on site (during deployment)."

Rick knows the value of preparation, because when he walked up on his first real-life mass casualty in 2003 while deployed to Afghanistan, he should have had more of it.

"We did a three-day ground assault convoy, I rolled up onto my FOB after not sleeping for 72 hours with my physician assistant in the back to a guy running in front of my truck, stopping and saying, 'hey, doc, we got a mass casualty at the Forward Surgical Team.' "

Rick, then a staff sergeant, walked in on 16 troops in varying condition. They had run into a firefight; none were wearing protective armor.

"They had been in a big gun fight," he remembered. "That was a chaotic event."

"The only way to manage that chaos is to rehearse it," he said, adding that his unit wasn't nearly as prepared for such an event as the infantry and artillery battalions in the 4th Stryker Brigade and his company of medics is currently.

"The more you do it, the more you learn," he added. "That's what we're trying to do for the Raider brigade is get it down before we go downrange."

Even Pvt. Jaime Medina, one of the company's newest medics, knows how real the possibility is that an actual mass casualty can occur downrange. He plans on being ready if the time comes.

"You should always hope for the best and prepare for the worst," said Medina, a Las Vegas native. "It's a very real possibility, and I like that we train like this."

But no matter the level of preparation, the chaos will always linger.

"In a mass casualty, there's chaos regardless, even if you have experience in it," said Porto after the exercise.

"The scenario's always different, so you can't avoid it."