Factual error: Oddball tells Kelly their commander had been trying to get them killed ever since they landed at Omaha (beach). Oddball's tanks are part of the U.S. sixth Armored division (the Super Sixth, as the unit shoulder patch on his jacket indicates) which actually landed at Utah beach on July 18, 1944. (00:30:50)
Factual error: When Hawkeye and Trapper arrive in Japan, as they approach the hospital in a Jeep, you can see a football field in the background. Look closely at the goalpost on the field. Instead of looking like an "H" (then in use), it is in the style used since the late 1960s: a bent single goalpost, a crossbar, and the uprights.
Factual error: Due to paranoid fear of sabotage, all Japanese Americans were interred in camps along the west coast during WW2. So it would have been MOST unlikely for Yamashita (especially considering his military background) to simply walk about freely and to have work as a gardener.
Factual error: When Clint Eastwood catches an Indian arrow in his left shoulder, he instructs Shirley MacLaine to prime the arrow shaft with gunpowder, which he then ignites as she forces the shaft all the way through his shoulder. Presumably, the burning gunpowder would cauterize the wound all the way through his body, or that's what the filmmakers asked the audience to believe. In reality, gunpowder is historically well-known for causing gangrene in open wounds. With a shoulder full of gunpowder cinders, Clint Eastwood should have died of gangrene and sepsis by the end of the movie.
Factual error: It's common in movies of certain eras to have cars catch fire when in real life they would not, and the car flip that concludes the chase at the beginning of the movie offers an example of that...but goes even further, much further, when you see the armored van impacting against the roof of the flipped car causing it to explode with such violence and inferno of flames coming from within the passenger seats you'd swear it had to be driven by giant dynamite sticks with arms and legs. (00:15:25)