Continuity mistake: While Father Mulcahy, Margaret, BJ, and Hawkeye are in the mess tent, when Colonel Potter walks over both of his shirt pockets are unbuttoned, but when he sits down the right pocket's buttoned up.
Continuity mistake: After BJ and Hawkeye taste Klinger's plateful of Spam Parmesan they all sit down at the table, and when BJ pulls the plate away from Hawkeye it cuts to another angle and the knife has jumped to the other side of the plate, and the fickle cup keeps sidling across the table to be beside the bowl depending on the angle.
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