Goodbye, Farewell, and Amen - S11-E16
Visible crew/equipment: While Klinger is on the phone trying to set up BJ's transportation home, just as Winchester walks into the office pointing out the company clerk the shadow of the moving boom can be seen on the wall, and it's also visible when Winchester takes the mailbag and dumps the contents. (00:42:50)
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