In rushed an out-of-breath Pfc. Merinda Karn with aid bag in hand for a test of her medic skills.

As insurgents have upped their tactics, the Army has increased the intensity of its training of battlefield medics. That's meant moving the training from sterile classrooms to more realistic scenarios and teaching medics to keep fighting the enemy -- even if it means sometimes delaying treatment of the wounded.

"One medic on his weapon returning fire can make the difference between the enemy staying and continuing to fire on us, or saying, 'Whoa, I got to go,'" said Capt. Brad Tibbetts, the officer in charge of the Alfred V. Rascon School of Combat Medicine at Fort Campbell. "That's one thing we teach them when to delay and when you can't."

This year, about 500 medics and others who work in small, isolated units will undergo training at the school. They attend the class partly to refresh skills they acquired during a 16-week course at Fort Sam Houston, Texas, where all new Army medics take civilian EMT classes and study battlefield techniques.

Much of the training at the Fort Campbell school is conducted using strikingly lifelike dummies controlled by computers. The dummies "bleed," breathe, blink and have a pulse.

Col. Richard Agee, chief of staff of the U.S. Army Medical Department and School, said the military is looking to expand its use of simulation centers like the one at Fort Campbell because more training could result in more soldiers coming home alive.

Of troops killed on the battlefield, about half die from bleeding, and the first 10 minutes after a soldier is injured is critical.

In the United States, it takes an estimated 15 to 30 minutes to get a trauma patient to a hospital. In Iraq it takes an average of two to three hours, and even longer in remote parts of Afghanistan.

Already, 89 percent of all casualties in Iraq are surviving compared to 73 percent in Vietnam and 78 percent in the 1991 Persian Gulf War. Agee credits better body armor and better training of medical personnel.

Participants at Fort Campbell who question the importance of their role need only look to Master Sgt. Luis Rodriguez, a former war medic who was hit by a mortar in Iraq. He lost a leg, but the use of a tourniquet helped save his life.

Rodriguez, the non-commissioned officer in charge of the training at the school, said the first thing he tells the medics is that the enemy will fire at them even if they are rendering aid, and they must be prepared to fight.

"The most important piece of equipment isn't your aid bag; it's your rifle," Rodriguez said. "We have to be aggressive, compassionate at the same time. But you have to bring the evil to the enemy."

The final test for the class at Fort Campbell started being conducted in a dark room after medics from the 101st Airborne Division returned from Afghan-istan and said they were not prepared to treat the injured without light. More physical intensity has also been added since the school opened in 2002.

Karn, 20, who weighs about 140 pounds, was out of breath when she ran in to take the test -- she had run 6 miles that morning and then pulled a 185-pound soldier about 200 yards before dashing into the room.

She failed the test because in the dark she failed to feel an exit wound in the back of her "casualty," and it "died."

Afterward, lights came on in the room and taps played. An instructor discussed what she did wrong.

"I just wasn't as thorough as I should have been," Karn said, before leaving the room to write a letter to the "casualty's" parents, also part of the medic training.

Tibbetts said it's OK to make mistakes here.

"I guarantee she probably won't miss it again," Tibbetts said. "If they learn it here, that's a good thing."