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.
Other mistake: At the end, after General Barker tells Henry that he should give Frank a high colonic and send him on a 10 mile hike, Klinger shows up in front of them supposedly naked, but we can see the top of whatever the actor's really wearing.
Character mistake: As Hawkeye goes to help Maj. Burns right at the end of the episode, he touches the patient with his bloody, contaminated gloves he used to work on the last patient. Such a blatant error would be anathema to any surgeon from the civilized world of the 20th century, let alone one of Hawkeye's caliber.
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