Visible crew/equipment: When General Barker opens the doors to Henry's office and finds Radar sitting behind the desk, we can see Barker's curved chalk foot marks on the floor beside the desk, where the actor will stand in a moment.
Henry, Please Come Home - S1-E9
Visible crew/equipment: After Reveille has blown, Radar comes in, and gets items thrown at him. As the door closes, there's a reflection of the studio lighting on the glass.
Love Story - S1-E14
Visible crew/equipment: After Radar tells Margaret that she's needed in the post-op ward Frank sneaks toward Margaret's tent, and when it cuts to Margaret walking into post-op, at the start of the shot we can see the two actors' curved chalk foot marks on the floor.
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