Factual error: When Klinger's walking with Captain Allen and the Stars and Stripes photographer, just before their introductions to "Ben" they pass an empty corrugated box with its flap open, and the recycling symbol can be seen on the flap. Recycling symbols were not in use until about 20 years later.
Other mistake: When Alan Alda and Mike Farrell are walking into frame in the scene where Hawkeye and BJ discover the huge shipment of tongue depressors, Alda's feet are visible for about two seconds and he has bright blue early '80s shoes on.
Visible crew/equipment: When the guy from I Corps Supply lifts the flap at the back of the truck with all the boxes, just as Colonel Potter says, "Sergeant, how many of these parcels are checking into this post," the shadow of the boom mic can be seen at the top, right corner of the screen.
Factual error: When BJ opens the first box of tongue depressors the tongue depressors are packaged in a plastic bag inside the cardboard box, my research says that plastic bags were not available in the early 1950's. (00:08:06)
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