UNDER THE WATCHFUL eye of a Marine gunnery sergeant, six young actors spent hours outside in the hot sun practicing military stances, salutes and, most importantly, how to carry a gun. Striving for military authenticity, director Eric Schaeffer put the actors of "One Red Flower," at the Signature Theatre, through their paces.

The play is based on the book "Dear America: Letters Home From Vietnam," a collection of letters to and from soldiers, edited by Bernard Edelman for the New York Vietnam Veterans Memorial Commission. Paris Barclay, a two-time Emmy Award-winning director ("NYPD Blue," "ER," "The West Wing"), inspired by the soldiers' letters, adapted the book for the stage. The play tells the story of six young soldiers deployed to Vietnam and is set to a 1960s rock score.

"We follow these six characters, become emotionally involved with them and experience what war was really like for them," Schaeffer says. "Based on actual letters -- and told through letters -- these are all very personal, firsthand moments, connected together over the space of a year."

Teaching actors the ropes of military life was a challenge. Initially, Schaeffer explains, the main goal of training was to instruct the cast on proper form, carriage and handling of weapons on stage. But the most important thing the actors learned, in the end, was how to come together as a team.

"Their cohesiveness really translates on stage," Schaeffer says. "They learned that it wasn't about the individual, but about the troupe, about taking care of your buddies, not just yourself. During the training, every time an actor said the word 'I,' the entire cast would have to do 20 push-ups. They learned pretty quickly to band together."

What may sound extreme proved powerful and effective for Stephen Gregory Smith, who plays company clerk Specialist Fourth Class Billy "Spanky" Bridges. He describes the training experience as both intense and humbling.

"It was during the first week of rehearsal, we were all still in breaking-the-ice mode, learning music and reading through our lines. Everyone seemed a little uneasy about the boot camp idea, all the team-building exercises and drills, when we barely knew each other."

Smith readily admits that the actors' day of boot camp was only a little taste, a "minute dose," of what the real thing is like. Smith's father, an Army veteran who served during the Vietnam era, laughed when Smith called to explain what he had been through, saying he "didn't know the half of it."

But after an afternoon spent crawling on his stomach with a prop gun, practicing military drills and pretending to carry casualties off the field, the 26-year-old Helen Hayes Award winner says it changed the way he looked at the world.

"It's given me a stronger appreciation for things I took for granted prior to this show," he says. "I have also visited the memorials more frequently. It's something I can do, to think of those men and remember them."

This is Smith's eighth show at Signature, and he claims this to be the closest-knit cast he has ever worked with, crediting both the boot camp experience and the play's text, the soldiers' letters home.

"It really isn't about us, it's about the words of these guys, these intimate letters that are so heartbreaking and engaging," he says.

Many nights after the performance veterans have approached Smith and his cast mates in the lobby, thanking them for paying tribute, for reminding others of their fight and struggle. Smith always turns it around, thanking them instead. "It's not about us," Smith says, "it's about channeling these words and bringing them to the ears of others."

For soldier Billy "Spanky" Bridges (Stephen Gregory Smith), letters bring back memories of home and his mother, Eleanor (Florence Lacey).