Continuity mistake: In some shots, Radar's exam questions are in his hand, in others they are tucked under his arm. (00:10:30)
Continuity mistake: When Frank is getting drunk he spills gin down the front of his vest. A few shots later, just before he collapses, it suddenly dries out significantly. (00:13:20)
Continuity mistake: During the charity no-talent night, when the curtain opens on the Swinging Surgeons we can see Radar using a set of brushes on the drums, but in Radar's closeups he's using drum sticks, then in the wideshot it's back to the brushes again.
Continuity mistake: Casey's glasses go from dark framed to metal framed and back as he says goodbye to Hawkeye.
Continuity mistake: At the end, Casey comes over to say good bye to Hawkeye. As he stands there, the glasses he wears go from round, speckled-brown frames to silver oval, and back.
Continuity mistake: When the Swinging Surgeons are performing during the charity no-talent night, Radar's drum kit is set up differently between the wideshots and closeups.
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