Continuity mistake: In the episode 'Chief Surgeon Who' (season one), near the end of the episode we see Radar in Col. Blake's office smoking a cigar with ease, but in the first episode of season six when Col. Potter offers Radar a cigar, he doesn't know how to smoke it and he throws up after he puffs it.
Continuity mistake: When Charles first arrives at the 4077, his scarf changes from shot to shot. It is tucked in neatly, then loose, then tucked in again.
Continuity mistake: When Colonel Potter, BJ, Hawkeye, and Charles are in the changing room, Charles wants to be alone so he takes his tan jacket off the first nail on the right and leaves, but in BJ and Hawkeye's closeups the tan jacket is still hanging on that first nail, then it vanishes again.
Continuity mistake: Charles and the G.I. lay waiting for an explosion. When the last mortar hits, the explosion is just to the left of the back tire, the jeep is untouched. After a cut, the jeep is trashed and burning.
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