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.
Dear Mildred - S4-E7
Visible crew/equipment: In the scene where BJ, Hawkeye, and Radar are in the motorcade talking about the horse, Radar is talking about how he doesn't want to give away the horse. He is standing in front of some barrels and when he moves, you can see some of the crew, the horse owner, and what looks like another horse in the background for 1 second.
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.
Visible crew/equipment: When Margaret listens in on Frank's phone conversation with his wife, Margaret throws a chair at him and storms out of the office, and after she calls Frank a chinless chipmunk a boom mic dips into view at the top, left corner of the screen.
Visible crew/equipment: When the camera angle changes to look at the cover being put over the soldier's head, the camera is briefly reflected until the cover is locked in place.
Visible crew/equipment: As BJ comes around to take the wounded soldier to Post-Op, he walks in front of the camera. As he does so, the shadow of the camera can be seen on his back.
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