From the Boston Globe (July 4 2004):
Robb's "Operation Hollywood: How the Pentagon Shapes and Censors the Movies" (Prometheus) documents the activities of the Pentagon's film liaison office, which is part of the Office of the Assistant Secretary of Defense for Public Affairs. The liaison office examines and demands changes to movie scripts to ensure that the US military is depicted favorably in the Hollywood productions to which the Department of Defense leases hardware or locations."
Well, that's kind of scary. People actually change their scripts in order to get assistance from the DOD. Some films that changed to get approval: Stripes, Thirteen Days, Heartbreak Ridge, Top Gun. Movies that were denied: Independence Day, Forrest Gump, Courage Under Fire.