Visible crew/equipment: When Frank climbs into the jeep belonging to Major General Cornell Dickering, the MPs show up at the same time that BJ and Hawkeye walk up to join the fun, and during this scene there's a T-mark (albeit a dusty one) on the ground at the driver's side of the jeep.
Visible crew/equipment: When Hawkeye removes BJ's Captain rank bars from his uniform and then pins it on Radar's knit cap, in the shot facing Hawkeye and BJ the shadow of the boom mic moves across Radar's back.
Visible crew/equipment: When Hawkeye and Radar are in the jeep heading to Kimpo Air Base they drive past the checkpoint, and in their closeups the camera casts a shadow on the hood of the jeep.
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