Factual error: On the map in Klink's office, the nearest town's name is Hamilburg. This a misspelling, as the real name is Hammelburg.
Factual error: The guard delivering the Russian captive in the tunnel at the start of the show has a paratrooper M1 carbine with a bayonet lug. Bayonet lugs were not attached to M1 carbines until after the war.
Factual error: While introducing himself to the downed Russian pilot, Hogan claims he is with the "US Air Force." He was actually with the United States Army Air Corps (USAAC) as the US Air Force wasn't formed until 1947, 2 years after the war ended.
Answer: It's a comedy, not a documentary.
stiiggy
Perhaps it was counterfeit. There are numerous episodes where they deal in counterfeit monies.