Factual error: In this episode, the regulars receive and respond to letters from a Fourth-Grade class in Hawkeye's home town. Charles receives one from a little girl who says she's sent him a birch leaf. Unfortunately, the leaf he removes from her glassine envelope is a maple leaf. (Note: there was no indication that this was supposed to be her mistake.)
New this week Other mistake: While celebrating the ceasefire, a Jeep full of people including Father Mulcahy stops between the Swamp and the main building. There's a streamer hanging down either side of Mulcahy from above the top of frame. Unless there's a power line to the Swamp that never appears at any time, there's nothing for it to hang from.
Other mistake: Across the show, several times doctors looking at an x-ray picture say things like, "Looks like he swallowed a whole junkyard" or "His belly is full of shrapnel." In fact, shrapnel, being metal fragments, should show up as clear white spots on the x-ray pictures, but none of that is visible in any of the x-rays shown throughout the show.