CAMP PENDLETON, Calif. — The only thing missing was "Ride of the Valkyries" blasting from the three helicopters as they swooped in to land at the military base.

But their arrival did not herald "Apocalypse Now;" it brought "Tropic Thunder."

Ben Stiller, Robert Downey Jr. and Jack Black choppered into the Camp Pendleton Marine Corps Base on Sunday evening for a special USO screening of the comedy, about selfish, pampered actors who go overseas to make a war movie and accidentally provoke real jungle warlords. The big-budget movie, which was filmed on Kaua'i, opens Wednesday.

It's rare for A-list stars to accompany an early free screening at a base — and unheard of for them to arrive in such dramatic fashion.

"It was pretty tame, actually," Stiller said after buzzing in over live-fire ranges, barracks and rolling hillsides.

"Sorry we couldn't get some explosions going off in the background," Lt. Ken Kunze joked as he greeted the actors at the base's landing strip.

"It felt like that kind of moment," Black told him.

Instead of the typical premiere's parade of limos, an entourage of Marines chauffeured the actors from the airstrip in armored Humvees.

"This is crazy," Stiller said as he donned a military-required helmet and flak jacket for the ride. "It's nice to be out of the norm, though."

The driver, Sgt. Clay Kirk, who oversaw prisoners of war as a field military police officer in Iraq, found celebrity duty much easier.

"Marines love you," he told Stiller, who responded, "Really?" with seemingly genuine surprise.

Stiller, who also directed and co-wrote the film, wanted to screen his work for the troops early because it mocks actors "who get everything wrong" about combat.

With Black and Downey by his side, Stiller told the service members and their families packed into the 1,300-seat theater at the base that he was inspired by actors from war movies who brag about the intensity of their movie-rehearsal boot camp.

"It seemed ironic to me, because I thought the fake boot camp was nothing like a real boot camp," Stiller said, drawing cheers before adding with mock arrogance. "It's about 10 times harder, you guys. ... From experience, I can tell you firsthand."

Stiller went on to explain: "The idea for this movie is, what happens when a bunch of actors get stuck out in the jungle in a real-world situation? Because us actors, most of us are, what, wussies?"

"Speak for yourself, Ben," Downey quipped.

Before the film began, a solemn video of "The Star-Spangled Banner" played on the screen, part of the theater's standard opening. It was an incongruous intro to the raunchy, R-rated comedy, but the audience didn't seem to mind.

During the show, the actors stood in the wings, watching the audience watch their movie, laughing when they laughed.

"Every movie audience should be like this," Stiller said. "It would be the best thing ever."