Revealing mistake: In the swamp during the movie, Frank comes up and talks to Igor, who is running the projector. Although there is a film running, there is no film on either the supply or take-up reels.
Factual error: In the beginning, Hawkeye says that the patient was full of shrapnel from a claymore. M*A*S*H was set in the early 50's, and the M18 Claymore was only in the development stages in 1952, and not accepted and battle used until Vietnam in 1961.
Frank Burns: I know I'm a real asset.
Hawkeye: You're only off by two letters.
Trivia: There were no American planes shot down over the Sea of Japan during the Korean conflict. It is rumoured that producer/director Larry Gelbart knew that, but wrote Henry Blake's death scene as he was very unhappy with the way Mclean Stevenson had left the show, and was determined to make it clear that there was no way he would be coming back.
Question: A number of times it is mentioned that the outfit is unarmed, yet several times, Frank has a rifle, or a pistol, and once Klinger had a grenade, and the guards and Klinger, while on sentry duty, has a rifle. Was this standard, or is this a mistake?
Answer: The Geneva Convention allows even doctors to carry a sidearm to be used in their self defense or the defense of their patients, however it is rare to do so.
Answer: As an old medical unit staffer, my experience is that med units have combat units assigned to defend them. Usually it was marines.
Answer: My old doctor (now deceased) served in Korea during the War. He was required to carry a sidearm anytime he was not in the hospital.
Answer: Even an Army field hospital would have SOME weapons for self-defense if the enemy attacked. What's meant is that it's not a combat outfit, and therefore wouldn't have enough weapons to actually attack anyone. (It's also mentioned a few times that the Officer of the Watch is supposed to carry a pistol at all times, but Hawkeye refuses to do it when he's in charge and Colonels Blake and Potter don't enforce the rule).
Captain Defenestrator