Factual error: In one episode in the hospital tent, Hawkeye hands a Hershey Chocolate Bar to a wounded soldier lying in bed. The back of the candy bar had a Universal Product Code (UPC) on it. UPCs were not used until the 1970s.
Factual error: Throughout the series, actors are seen wearing cuffless permapress fatigues. Neither cuffless nor permapress utilities were available until the 1970s.
Factual error: Throughout the series, there are repeated instances of "I Corps" being pronounced, "Eye Corps." Since Army corps are designated by Roman numerals, it should be pronounced, "First Corps." (I wonder how they would have pronounced "III Corps" or "XVII Corps?").
Factual error: Nearly every show depicts the use of disposable plastic syringes, which weren't introduced till 1955, two years after the war ended.
Factual error: The Spot-A-Card pinball machine in the Officers' Club didn't come out until the 60's.
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