Continuity mistake: After doing his pushups, Colonel Brighton puts on a red robe and talks with Trapper and Hawkeye. In some shots the cord from the robe's hood is hanging down and in others it is tucked in. (00:10:20)
Continuity mistake: When Frank is trying to examine the Colonel, in some shots Buzz's robe is open and in others it is tied at the waist. (00:10:50)
Continuity mistake: When Radar is slipping the glass of milk into Buzz's tent, we see the outside of the tent and there are no windows. From the inside, the milk is placed on a table that is right under a window. Also, the milk is already on the table in a scene before Radar puts it there. (00:13:20)
Revealing mistake: As Buzz is stopped at the tent door by Hawkeye and Trapper, the vertical edge of the "sky" is seen over the top of the hospital building, behind the camo net.
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