Character mistake: Some of Colonel Jessup's ribbons are in the wrong order, and his Combat Action Ribbon is backwards.
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.
Character mistake: When LTJG Kaffee says "whatever happened to saluting an officer when he leaves the room?" It's well known that Kaffee doesn't know much about military protocols, but Marines and Sailors do not salute while uncovered, especially indoors. Army/Air Force maybe, but not the Navy or Marine Corps.
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.