Continuity mistake: While Trapper and Hawkeye are lying on their cots, one by one everyone joins them in the Swamp, and in Trapper's closeups the "USA sterilized" that's printed on his pillow is upside down, but in the wideshots his pillow's flipped over with the print right-side up.
Visible crew/equipment: Before the meeting in Henry's office starts, when Margaret and Frank take their seats, under Frank's chair we can see the chalk T-mark on the floor behind him.
Continuity mistake: When in the Swamp, and they show Hawkeye numerous times, the door to the stove is open, then closed, then open, etc.
Revealing mistake: There is a lag between the interior lights going out and the exterior stage lights going on.
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