THE MORNING sun is jungle-hot, and Capt. Ryan Rentschler shifts uncomfortably in his Army fatigues.

He grabs his gun, an M-16 A1 rifle, and strides over to pluck a machete and conical Vietnamese farmer's hat off the ground.

On this balmy day, Rentschler is not hot on the trail of an elusive Viet Cong sniper in Saigon.

Rather, he's at his New London, Chester County, home, taking inventory of a pile of authentic 1960s- and '70s-era military gear and garb - props he'll use during a Vietnam Veterans Appreciation Day re-enactment this weekend at Fort Mifflin, in Southwest Philadelphia.

When it comes to war re-enactors, soldiers in Civil War and Revolutionary War uniforms are a dime a dozen.

But a growing and controversial group of history buffs like Rentschler have been re-enacting more modern conflicts, such as the Vietnam War.

Participants say re-enactments give much-maligned veterans some overdue appreciation while educating a public that learned little in school about the nation's longest war.

"We're not out to glamorize war; we're out to preserve the memory of these veterans," Rentschler said. "Some people like to think of re-enactors as militants. We're teachers, we're historians, we're exploratory archaeologists. We're not militants."

But critics wonder whether the theatrics sensationalize a conflict whose veterans would rather not relive the horrors they survived and who continue to grapple with still-raw resentments from sour homecomings.

"I have enough re-enacting going on in my head," said veteran Al Maberry, 61, of South Philadelphia, who served two tours in Vietnam between November 1969 and September 1971. "I saw enough and remember enough that I don't think I'd care to go to a re-enactment."

And how, some wonder, do you re-enact a war whose action involved bombing villages, spraying Agent Orange to defoliate jungles, dodging hidden booby traps and trading gunfire with unseen, blast-and-bolt snipers?

Harvey Siegel, 64, of Yardley, who spent nine months as a Marine aviator in Vietnam in 1968, says: "Kids today, you say 'Vietnam,' and they give you a blank look; they couldn't find it on a map, nor could they find Iraq on a map, if their life depended on it. So I understand the education part of it, so long as they stay away from the politics.

"But how do you re-enact it?Are you going to have other guys dressed up as Viet Cong, and are you going to shoot them, and are they going to fall down? Are you going to re-enact me, hauling [via helicopter] supplies into a Vietnamese village? I just don't get it."

An old hobby

War re-enacting in the United States is almost as old as the country itself.

In 1822, less than 50 years after the American Revolution, about 20 veterans re-enacted their 1775 clash with British troops at Lexington, said historian Jenny Thompson, author of the 2004 book "War Games: Inside the World of 20th-Century War Reenactors."

Since then, the U.S. military has re-enacted battles to train soldiers, and re-enactments long have been a part of commemorative ceremonies, Thompson said.

Thompson, who spent seven years researching and participating in re-enactments for her book, estimates that more than 6,000 people participate in 20th-century war re-enactments, compared with tens of thousands in the Civil War "hobby."

What motivates participants varies vastly, Thompson added.

Some do it to indulge a love of history, weapons or collecting, she said. Others want to educate the public or honor veterans, victims or ancestors.

Some get juiced by the thrill of playing war.

For Rentschler, it's all of the above.

At 25, he wasn't even born when the Vietnam War ended in 1975.

But war is his hobby and career.

Rentschler is commander of a Vietnam War re-enactment unit, founded in 2003, called Delta Troop, First Squadron, Fourth Cavalry Regiment, First Infantry Division. It was a real unit in Vietnam, the one in which the father of his buddy Mark Prestianni served as a radio operator.

Rentschler also collects militaria, selling it at re-enactments and online. And he takes road trips regularly during the school year to the Army Heritage and Education Center in Carlisle, Pa., where he is a historical interpreter.

He also has portrayed soldiers in History Channel programs on Civil War combat and in a commercial on the Armed Forces Network. When he married wife Joanna last year, he wore a Revolutionary War militia officer's dress uniform.

He got into re-enacting as a teen at Civil War and Revolutionary War events, but it was an experience he had in the real Army that drew him to Vietnam War re-enacting. After enlisting at age 18 after 9/11, he was stationed at Fort Indiantown Gap, Pa.

"I had a run-in with some hippie-types who spit on me," Rentschler said of war protesters picketing the fort. "According to them, I was a fascist pig. I'd always been fascinated by the Vietnam War, but that made me want to do something to honor these guys [Vietnam veterans] who took a lot worse abuse than I did."

Rentschler, who left the Army after two years because of injury, prefers to call what he does "living history." He rarely participates in mock battles, or "tactical scenarios," because "that's too Hollywood."

"There's no real comparison; there are no bullets flying, nobody getting their heads blown off," Rentschler said. Still, "we do it sometimes, because the public wants it."

Last week, Rentschler and buddy Prestianni spent a day organizing all manner of militaria that they'll display at this weekend's re-enactment, including authentic weaponry and uniforms, old Playboy magazines, chemical weapons masks, rations and Chieu Hoi ammunition bags.

They even have period recordings of Armed Forces Network public-service announcements on everything from handling snakes (try to kill it, but remember "the snake is sometimes faster than the hand") to venereal disease ("if you're worried, see your medic").

Both are sensitive to the outrage their hobby can engender.

So they work hard for acceptance: They "screen" new re-enactment recruits to weed out those who would "act crazy," they require recruits to go through a "boot camp" to improve their authenticity, and they don't wear Purple Hearts or other unearned combat badges.

And although both also participate in World War II re-enactments, they will portray Nazi soldiers only during private events, to avoid offending anyone at public events.

Stereotypes and Hollywood hype are forbidden, Prestianni added.

"War crimes happen in every war, and we don't want to dispel that that happened. Some people lose their minds in war, because war is hell," Prestianni said. "But we do not portray hippies or druggies, baby-killers or ear-cutter-offers."

Terry Williamson has never heard of Vietnam War re-enactors. But he's not surprised they exist.

"There's a deep-seated interest in this country in military matters," said Williamson, president of the Philadelphia Vietnam Veterans Memorial Fund, who served in Vietnam in 1968 and 1969 as a Marine combat infantry officer.

He'll be celebrating veterans today at the Philadelphia Doo Wop Festival at Penn's Landing. But he hopes to stop by Fort Mifflin and see Rentschler's unit.

"You read about this stuff, and re-enactors give you a chance to see it in person," Williamson said. "It's like history coming alive."