Visible crew/equipment: When Father Mulcahy and the farmer are talking to BJ and Hawkeye about the wounded cow, the doctors say they'll get help from Colonel Potter, and when they walk away the T-mark can be seen on the ground where they were standing.
Plot hole: In this episode, Margaret is required to give a lecture on the use of Levophed, because it is being introduced. However, in the Episode "Period of Adjustment"(8-6), Hawkeye orders an IV of Levophed for one of his patients. (00:12:15)
Other mistake: When the scene is of the cow in the barn, the background hilly area can be a painted backdrop.
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