The danger can come out of nowhere, often after long hours of boredom.
In a turret of his humvee, Army Sgt. Matt Patterson of Bass River Township, Burlington County, stood watch behind a 50-caliber machine gun Tuesday while another member of his unit met with an Afghan elder to discuss ways of improving local security and ending nightly Taliban incursions.
Staff Sgt. William Schnell of Newark, Del., told the Afghan leader he cared about the community and was a family man like him. He had just produced a picture of his daughter when the peace was shattered by an explosion. A woman had stepped on an improvised explosive device.
Patterson swiveled his gun toward the sound, then - ordered by Schnell - drove to secure the area and evacuate the wounded. Would they be met by enemy small arms fire? Rocket-propelled grenades?
All of the weeks of training at Joint Base McGuire-Dix-Lakehurst, classroom instruction on Afghan customs, working with veterans and interpreters, came down to this moment, in which Schnell, Patterson, and their comrades worked together to "save" a life and preserve the peace.
But this "Taliban attack" and others at mock villages at the South Jersey base are simply practice runs for more than 120 members of the Delaware Guard's 153d Military Police Company, which this month will begin mentoring Afghan police.
No one is really hurt in the exercises. Here - in this safe environment - they learn from mistakes and build on success.
"This is outstanding training," said Patterson, 27, who also served in Iraq. "The focus is on supporting the Afghans, on working with them and through them.
"We want them to take over their own security and be a more prosperous, stand-alone nation."
The soldiers from Delaware, New Jersey, and Pennsylvania are heading to America's longest war. President Obama and Afghan President Hamid Karzai announced last month that the U.S. military would soon complete its combat mission in Afghanistan and shift into a supporting role leading up to the "responsible end" of the war in 2014. About 2,000 Americans have been killed and 18,000 wounded.
Taking part in the transition means that members of the 153d must themselves be mentored by trainers in the 174th Infantry Brigade, First Army Division East.
The Delaware unit - headquartered in Delaware City -- was deployed in 2007 to Baghdad and Kalsu, where many members of its ranks worked with Iraqi security forces.
Tuesday's field exercises were meant to put what they have learned about Afghanistan to the test.
The soldiers have received police combat training, marksmanship drills, and instruction on patrolling and how to counter explosive devices. They also have been working with several Afghans, who provide a realistic environment. On Tuesday, the Afghans were told to cover their faces when pictures were taken, to avoid retaliation against their families in their country.
"I want to help my country and the American military," said a man who gave his name as Said N., 52, a former Afghan farmer who now lives in Bethlehem, Pa., and serves as the elder of one of the mock villages. "I tell [the soldiers] that when they go to a village, find the police station or a mullah."
At a village dubbed Chakab, one of the trainers in the 174th, Dave Chambliss, 30, of Maple Shade, had taken on the role of an Afghan police officer - at least on the surface. For Tuesday's exercise, he was a Taliban inside man, ready to attack as soon as the enemy opened fire.
The Delaware guardsmen "have to learn what the Afghan police need and what the village needs," said Chambliss, who played along with mentors.
"We want you to branch out to other villages," Sgt. Drew Duelfer, 27, of Wilmington, said through a real Afghan interpreter. "I don't want to insult your intelligence; you know how to patrol.
"But are you familiar with walking an 'S'?" he said, demonstrating a walking and turning motion. "You can avoid snipers. Does that make sense?"
One of the 174th's trainers, Sgt. First Class Panki Miah, 31, of Paterson, N.J., watched the interaction. "I'm pretty sure this training saves lives," he said. "They get a lot out of it."
The Guard soldiers were supposed to show the Afghans how to patrol -- and possibly evict some nearby Taliban squatters -- but as the exercise got under way, the village was rocked by explosions, followed by the pop- pop-pop of automatic gunfire. Clouds of smoke wafted through the air.
One of the gun-mounted humvees had been "hit" by a rocket-propelled grenade and put out of commission. The soldier in the gun turret was "severely wounded" and needed immediate evacuation. His comrades helped drag him to another humvee, then drove to a safe spot nearby, where green smoke marked the spot where a helicopter could land to evacuate him.
With them busy, Chambliss, the Taliban infiltrator, "shot" three American noncommissioned officers using blanks before being eliminated by a soldier firing a turret machine gun. Two of his "victims" had flesh wounds, and a third was saved by his bulletproof vest.
Soldiers such as Patterson believe they can make a difference and bridge the cultural divide. "I feel they really do want the help and appreciate it," Patterson said.