Plot hole: The boys take out the radio control unit from the mini tank. Le Beau is needed to get in and drive it to make it appear okay. After going between the buildings, they get him out, and start it on its way. Trouble is, no remote control and no driver, yet it turns and operates smoothly.
Audio problem: As the baby tank runs by the group in a wide shot, you see Hogan's mouth moving in a conversation, but the words don't match up.
Revealing mistake: As Hogan goes through the hole to the ladder, the "rock" he brushes against flexes for a second. Likewise, when Kinch climbs through, the "rock" under his hand flexes and mashes down as his weight is on it.
Factual error: In the very end, Klink comes up to the boys. As he stands beside Hogan, the Desilu Studios Water Tower is present behind them.
Answer: It's a comedy, not a documentary.
stiiggy
Perhaps it was counterfeit. There are numerous episodes where they deal in counterfeit monies.