Lt. Cmdr. Chris Gillette, the National Naval Medical Center's master of disaster, was ready. At a word from the chief, a firetruck, siren wailing, raced down the road, coming to the scene of a gory terrorist attack that had existed only in his mind six months ago.

It took that long to prepare for yesterday's annual mass casualty drill at the Bethesda hospital, a dress rehearsal for the darkest national nightmares. Involving more than 4,000 personnel from the Naval Medical Center alone, and hundreds more from the neighboring National Institutes of Health, Suburban Hospital, and Montgomery County police, paramedics and firefighters, it was supposed to simulate what emergency workers would do if confronted with a terrorist attack or natural disaster.

"The hardest part about re-creating this is re-creating the realism," Gillette said as victims screamed for help and firefighters piled out of their truck. "We have to get them out of the mindset, 'This is just a drill.' "

To that end, he tried to bring a bit of Hollywood to Bethesda, stockpiling gallons of fake blood and "moulage," the term of art for gory makeup, and recruiting costume experts to apply it properly. He obtained canisters labeled as anhydrous ammonia, a suffocating gas that burns the eyes and skin of victims. Then he came up with a devious plot: The terrorists would crash a van loaded with the chemical into a group of morning joggers at the base, coordinating the act with other planned truck crashes across the county.

Finally, Gillette wrote orders for each of the hospital's 115 volunteer victims, which they wore on cards tied around their necks, and coached them on how real victims would behave in a disaster. After the Katrina and Rita hurricanes, it was not difficult to persuade people to take the situation seriously, he said.

After a final briefing at 6:30 a.m. yesterday, he unleashed this hellish scenario on the hospital's staff and watched what happened.

"I get the luxury of coming up with all the ideas," Gillette said as firefighters assembled a yellow and white tent where the victims would be decontaminated. "I should write for 'Desperate Housewives.' "

Gillette looked with satisfaction at the surreal scene on the other side of a strand of police tape, where screaming victims ran in circles and simulated gas from a smoke dispenser wafted out in the wind. Fifty exercise controllers took notes, evaluating how things were going. Gillette had a clipboard listing the 64 events on the exercise's timetable.

Victim No. 15, Hospitalman Kojo Enchill, had cuts on his face, and his arms were bloody -- mild injuries, compared with the poor fellow lying unconscious, with a piece of pipe sticking out of his chest. "Male/Female fell while running from van explosion. Very anxious and upset," Enchill's light blue card said. He played the role of panicky patient with Oscar-worthy gusto.

"We got about 10 people dying, and we are getting no help!" Enchill cried as firefighters tried to sort those who needed immediate care from those who could wait.

"I can't see! My arms are burning!" other victims yelled.

One of the firefighters, Capt. Gabe Morlan, wanted to take Enchill to the decontamination tent, but Enchill was too upset to listen.

"Knock him out, I don't care," Morlan told a fellow firefighter. "He's starting to wear on my nerves."

They eventually dragged him by his feet. He went through the tent, where he was hosed down to get the chemical off his skin, and was loaded with other victims onto a bus, which waited awhile before going to the emergency room, causing the passengers to get more restless.

"Send FEMA," one victim yelled out the window. "At least they'll be here next week!"

"I need some beer before I die," Enchill whimpered.

Back at the scene, Gillette was pleased, both with the enthusiasm shown by his actors and with the professionalism of his staff. An aide told him that there was a complication: There had been a real three-car accident on Rockville Pike, the main road to the hospital, and ambulances would have to route around it.

Gillette smiled. "Perfect."

During the National Naval Medical Center drill in Bethesda, firefighters pretend that a crash has released a gas that burns the eyes and skin of victims.Disaster "victim" Kojo Enchill demonstrates his acting skills as he screams for help at the scene of the mock terrorist attack.