Gen. Barker: What are you doing?
Radar: Doing, sir?
Barker: D-O-I-N-G. Doing. What are you doing?
Radar: Uh, listening to you spell doing sir.
Barker: Doesn't Col. Blake mind you drinking his whiskey and smoking his cigars?
Radar: Oh, very much so, sir.
Barker: Then why are you doing it?
Radar: Well, I don't mind, and I figured as long as one of us was being reasonable.
Frank: Haven't you two anything better to do when you're off duty than to lie around and swill gin?
Hawkeye: Swill gin?! Sir, I have sipped, lapped, and taken gin intravenously, but I have never swilled.
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