Continuity mistake: The length of the chewing gum hanging from Henry's hat differs between the front and rear shots. (00:03:10)
Factual error: When Frank sits down on Margaret's bed, he pulls a single metal star out of his butt. Kelly being a Lt. Gen, he should have (and has, as can be seen in other scenes) a single bar of three interconnected stars, not three single ones. Therefore Frank shouldn't be able to find a solitary star in Margaret's bed. (00:19:00)
Factual error: Radar gives the location of the battle as Longitude 70, Latitude 27. This means the Korean war has spread to India. (00:21:00)
Continuity mistake: After Iron Guts Kelly dies in Margaret's tent, Frank Burns visits Margaret, suspecting something. Frank asks why there is a general's star on her cot. In the ensuing 'back and forth' dialogue, Margaret's hair goes (in close ups) from nicely combed, to frazzled, back to nicely combed again (and in a different light).
Continuity mistake: In the episode Iron Guts Kelly, Col. Wardman first calls Iron Gut Kelly a Lt. General, then a Maj. General then he goes back to Lt. General.
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