FORT HOOD, Texas – The first crackle across the radio of "shots fired" didn't provoke much concern.

Probably someone throwing firecrackers off the roof again, thought Sgt. Andrew Hagerman, a military police officer on his rounds in the barracks area, about a mile and a half from the Soldier Readiness Processing Center.

In his patrol car, the "shock and awe" came, he said, when he heard, "Officer down." With sirens blaring, he made it to the scene in three minutes.

"It was controlled chaos," Hagerman said.

Maj. Nidal Malik Hasan had created a battle scene worse than most had witnessed in Iraq.

Hagerman and Fort Hood medical personnel offered the first detailed account of Thursday's mass shooting, which left 13 dead and more than two dozen hurt. They described a bloody scene, but one where military and medical training quickly kicked in, and soliders, doctors and nurses worked furiously to save lives.

When Hagerman arrived, people were screaming. Some were on the ground, with soldiers hovering over them and ripping off their own shirts to stanch the bleeding. Some were being carried out of the two buildings where most of the carnage had occurred.

"I did spin a circle a couple of times, thinking, 'What do I need to do here,' " Hagerman said.

He walked past the gunman, unconscious on the ground in military fatigues. Ambulance drivers and medics had arrived and with his training taking over, Hagerman began directing traffic and sorting out the most serious who would need an ambulance first.

Military and civilian police responded to the shooting within five minutes, said Sen. Kay Bailey Hutchison, who visited Fort Hood on Friday. It appeared a tremendous amount of damage was done in a short amount of time.

"Soldiers are prepared to lose their lives for their mission. You’re never prepared to be cut down by one of your own."

About the time Hagerman heard the first reports of shots fired, Col. Steve Beckwith, a doctor and triage expert, was tending a patient at the post hospital. A nurse told him there were some gunshot injuries needing attention.

He started dispatching ambulances, then heard from his first driver that shots were still being fired.

"I heard there were dead on the scene. There were reports of a lot of casualties," Beckwith said. But his first flicker of concern was for the medics he'd sent into harm's way.

He made his way to the ambulance bay and already cars were pulling up – soldiers, rushing to a battle scene, picking up the wounded and taking them to the hospital before ambulances could even arrive.

"The first eight came in their own vehicles," he said.

Soon the ambulances started in a stream that would continue for an hour. About 35 casualties would bang through the ER doors, and Beckwith had to assess each.

"There were all sorts of makeshift bandages out there. A lot of them got care before they got to the hospital," he said.

Most were chest, trunk and extremity shots, which he dispatched. One had to be pronounced dead just as the victim was pulled out of the ambulance. Busily checking vital signs and issuing orders, Beckwith said he thought: Good, we can save most of these folks, he said.

The wounded tried to help him prioritize. "People would be saying, 'Hey, I just got a leg; go get that guy,' " Beckwith said.

For ER nurse Janet DiPalma, the word came when a fellow nurse stuck her head into the office, announcing that there were multiple gunshot wounds coming in.

As she headed for the doors, she heard staffers on the phones with nurses and other medical personnel, some who didn't work at the hospital, who were calling and asking if they could come in and help.

"It was very intense," DiPalma said. "Soldiers were carrying soldiers. One was coming in right after the other. Your adrenalin kicks in."

It began right after 1:30, and the blood-soaked train continued. After about an hour, DiPalma said, she looked up and thought: "How many more?"

Col. Kimberly Kesling, chief of medical services, was at the hospital going into a meeting when an aide gave her and other top commanders the word of an ER on full alert. She thought initially it would be a relatively minor thing, a single patient or maybe two.

By the time she got to the ER, "it quickly became evident that it was a massive event," Kesling said.

In short order, Kesling said all six operating rooms were filled with teams working on the injured.

Within an hour and a half, some had been airlifted to other hospitals, some were being treated, some in surgery Things had calmed down, she said.

Kesling said she was proud of her staff. Going from station to station, "I didn't see a cracked emotion," she said. "Today, tomorrow, that might be a different thing."

A surgeon, she had served in Iraq for nine months, returning in January 2004. For Kesling, the comparison was too real.

"I'd hoped to never see anything like that again."