Character mistake: During the trial, Danny says Lt. Col. Markinson shot himself in the mouth with a .45, but in the suicide scene, Markinson's gun is a Beretta 9mm, the standard-issue U.S. Military sidearm.
Suggested correction: It's likely Danny never knew the model of the gun that Markinson used. His point was to tell everyone (mainly the jury) that Markinson had committed suicide by shooting himself. Danny mentioning the model of the gun was not his point, he just did that for added effect.
Character mistake: Lt. Caffey (Tom Cruise) wants the two marines to plead guilty and take a deal because he doesn't want the to "spend the rest of their lives in Leavenworth (prison)." The United States Disciplinary Barracks is indeed located in Leavenworth, Kansas. And the US Army and US Air Force send convicted felons there to do their time. However, Marines and members of the United States Navy are sent to Portsmouth Naval Prison in New Hampshire. It is run by the Marines.
Suggested correction: It's perfectly within character that Caffey wouldn't know this. He's been in the navy a short time, never tried a case in a courtroom, and is generally uninterested in military protocol.
Portsmouth has been closed since the 1970s. Left abandoned because it was too expensive to rebuild or demolish.
Other mistake: When Danny, Sam and Jo arrive on Guantanamo Bay Naval base, they are met by the driver who recommends they put on camouflage jackets so their dress whites won't be spotted by Cuban snipers distinguishing them as high ranking targets.They comply and as you see them drive away, right there on the top of their heads, bright white dress hats can be seen clear as day. While it's against regulations to remove hats outside, it's also against regulations to cover dress whites, so a half-assed measure is an odd choice.
Suggested correction: The white shirt with shoulder boards are proper for officers, and a sniper would recognize the target as one. White hats are worn both by marines and sailors of all ranks, and from a distance, the differences may be not so easy to spot.
Character mistake: After Dawson and Lt. Caffey have their heated argument Lt. Caffey storms out of the interrogation room. He stops at the door and asks Dawson why he isn't saluting a superior officer leaving the room. The fuming Dawson gets up and defiantly jabs his hands in his pockets. Dawson is actually following correct procedures. Military prisoners are not allowed to salute anyone.
Suggested correction: This is more a mistake on Lt. Caffey's part, whether deliberate or not. He knows that Dawson should not salute him, but he wants to make a point about outranking Dawson.
Marines are not allowed to put their hands in their pockets; it is against regulations. Dawson doing so is a major "screw you" to Caffey and the regs in general.
Remember Daniel Kaffee is a Navy lawyer of very limited military experience. He may well have thought he was to be saluted as he left the room. Corporal Dawson, being a Marine would know this wasn't required, so the hands in the pockets is definitely an act of defiance.
