Tom Clancy's The Sum of All Fears has been criticized as being too realistic — but realism is exactly what the filmmakers wanted.

In fact, moviemakers who create spy and military films rely on a host of government experts to ensure that everything from sets and uniforms to planes, protocol and plot are as realistic as possible.

"Paramount sent us the [Sum of All Fears] script and asked us to comment on the degree of realism," said Chase Brandon, the CIA's film liaison. "It certainly took some poetic license … But overall the script was a good read."

Brandon, who spent 25 years as a special operations officer in the CIA, worked with the film's director, Phil Alden Robinson, to hone the details of the script.

"Phil especially wanted to make this as realistic as he could while still having this based on a fiction piece," Brandon said, "I was struck by how realistic the premise was."

In answer to the question of whether audiences are ready to see such an authentic look at terrorism, Morgan Freeman, who co-stars in the film answered: "Yeah. This is a big country. We are courageous and we are not easily frightened, and this is just a blankety-blank movie."

And Ben Affleck, who plays CIA analyst Jack Ryan, told Fox News: "If you feel deeply affected or so traumatized that you don't necessarily want to see anything that has anything to do with terrorism ... I certainly would understand that."

However he added, "By the same token I'm really proud of the movie ... I think it's not just about terrorism but about recovering from disaster."

While the CIA opened up parts of its headquarters to set designers and actors, Brandon emphasized that government secrets aren't revealed to outsiders — no matter how famous they are.

"Ben sat at the desks that are occupied by the real Jack and Jill Ryan," said Brandon. "But he's not thumbing through desk drawers and looking through people's rolodexes."

The practice of calling on the government for expert advice started during the silent film era. The Department of Defense first aided filmmakers on the 1927 World War I drama Wings, according to Department of Defense film liaison Phillip Strub.

And the tradition continued from there. Films such as Black Hawk Down, Air Force One, The Right Stuff, and Behind Enemy Lines have all gotten cooperation from the appropriate branches of the military.

But even with all the expert advice, movies clearly stretch the truth for dramatic effect.

"Sometimes even in pictures we work on, the details are inaccurate, but it's a movie, it's fiction. We don't expect it to be totally accurate," said Strub. "If we were in charge, [the films would] probably be totally boring and no one would go see them."

As an example of a "wildly unrealistic" film moment Strub cites the Steven Seagal, Kurt Russell flick Executive Decision. In one scene a special forces team secretly boards a commercial airliner that has been taken over by terrorists.

"That whole notion of the aircraft through which they inserted a special forces team is totally unrealistic," Strub said. "It looks like a Stealth Fighter, which is unrealistic. But we thought, 'We'll accept that as artistic freedom as long as what they do once they get on the plane was realistic.'"

As for members of the military, they try not to be bothered by inaccuracies on the big screen.

"It's often a source of amusement and head-shaking," said Frederic Peterson, a former lieutenant colonel in the Marines. "It distracts from the credibility but not necessarily from the entertainment value.

"People who have been in the military notice the most minute details that would pass by the general public."

Among those details Peterson cites are a "smattering of ribbons" on uniforms that don't make sense, belt buckles swapped between branches of the military and silly haircuts.

"Some of these actors have the need to preserve their own Hollywood demeanor," he said. "Particularly Tom Cruise. He can't get a proper [military] haircut."

The degree of help the government gives filmmakers depends on several factors including the availability of personnel and equipment, according to Strub.

Sum of All Fears is mostly a CIA picture, but the Department of Defense helped out in a few key scenes, said Strub. "The Marines provided some helicopters for filming," he said. "And the Air Force allowed air-to-air filming of one of our airborne operations centers."

But while the military seems to go out of its way to help certain Hollywood films get it right, the CIA's Brandon emphasized that the government still has its own priorities in line.

"We're not here to make movies," he said. "We're here to keep the country safe so people can make movies, to guard the country's freedoms."