Henry Blake: Klinger! It's four o'clock in the afternoon and you're still in a housecoat? Put on a dress! You never know who might be coming around.
Frank: [after Hawkeye hits him] Captain Pierce, I accuse you of striking a superior officer. A court-martial offense under the Articles of War. And I have two witnesses!
Trapper: [to Hawkeye] I didn't see anything, did you?
Hawkeye: My back was turned. [Drops towel in Frank's face.] BA-DUM-BUMP!
Trapper: Case dismissed.
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