Visible crew/equipment: When Frank and Hot Lips are walking into the mess tent for Frank's surpise party, if you look in the window to the right of the door, you can see a person silhouetted, throwing leaves into the wind.
Continuity mistake: In Henry's office, the white cloth Radar has on his ears changes positions from shot to shot.
Continuity mistake: As Radar is sorting mail, and Trapper makes a joke, Radar starts to put a letter down. After the angle change, he puts the letter down again.
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