Revealing mistake: At the end of the scene with the destroyed bridge, when Oddball's Sherman drives away, Cowboy is nearly left behind and climbs onto the rear of the tank by standing on a box attached to the rear plating. The next time we see this tank from the rear, the box is gone. It was obviously there only to help Cowboy climb on.
Character mistake: In the scene where Crapgame is sitting in the back of the truck at the end, when the men are loading Kelly's squad's take after splitting with the Germans and Oddball, Crapgame asks Fisher to verify his calculations. There are 125 boxes of gold left valued at $8,400 per box. Fisher says that they are worth $10.5 million, and each of the twelve men in the squad will get $875,000. The actual amount (125 x 8400) is $1.05 million, making a per man take of $87,500. He's off by a factor of 10 one way or another.
Factual error: In the final shot of the movie, the Tiger tank/T34 is seen driving away emitting masses of diesel smoke common to the Russian T34. However the Tiger was a petrol tank, not a diesel, as mentioned by the German tank commander. The Sherman was also petrol and well known for its ability to catch fire when hit. It was nicknamed the 'Ronson.'
Factual error: Near the end of the movie the general and the army convoy drive through the town and are stopped by all the celebrating going on. If you look at all the cheering villagers, you can see they are dressed in modern (for 1970) clothes and have hairstyles that were not around in the 1940s.
Factual error: 14000 bars of gold would be hundreds of tonnes, more than the capacity of the one truck. A standard gold ingot weighs 12.4 kilograms. 14000 would weigh 173.6 tonnes. Even if they divided the haul evenly between Kelly, Oddball and the Germans they would be hauling away just under 58 tonnes of gold each, way, way beyond the capacity of anything on the roads in those days.
Continuity mistake: When Kelly comes to make a proposition to Mulligan, the sun is on Mulligan's back. When both are in the shot from Kelly's view, both are in the sunlight. Then at the, "I need an authorisation" reverse shot, they are both in the shade, these 2 scenes are obviously shot at two very different times.
Continuity mistake: Two of the German SS Tank officers are walking together through the streets of Clairmont chatting. In the first scene with them, the officer on the left carries the rank of 'Obersturmführer,' denoted by his lapel badges, and the officer on the right has lapel badges showing him to have the rank of 'Sturmbannführer' (although both officers' shoulder badges show no correlating rank to their lapels). However, in the second scene with the same two officers still walking and chatting, the officer on the right has been demoted as he is now showing the rank of 'Untersturmführer.' (01:44:20 - 01:45:40)
Factual error: Almost all the German soldiers in the movie are armed with MP-40 SMGs. In fact, most German infantrymen during World War II were armed with Mauser rifles. MP-40s were only issued to squad leaders and officers.
Continuity mistake: The Tiger tank blows a hole in the bank door, so the team can gain access. A check made previously for another entrance was obviously not successful since it was necessary to blow the hole with the tank. Kelly et. Al enter through the hole but immediately are joined by others from some unexplained side entrance.
Factual error: The "BAR" carried and fired in the movies is actually a FN-D Model that was never issued by the US Army in WWII. It was developed post war in Europe. Also the Thompson machine guns and the 1919A4s are all firing at a accelerated rate of fire, much faster than normal. This can be attributed to the weapons being blank adapted.
Factual error: During Oddball's raid on the German train station, you can hear a radio playing 'All For the Love of Sunshine' by Hank Williams Jr. Hank Jr. wasn't even alive yet, let alone making records during WWII. The soundtrack to the film also contains the song, "All For the Love of Sunshine," which became the first No. 1 country hit for Hank Williams, Jr.
Factual error: When the raging Tiger is shooting around we can see that the muzzle brake of his gun stands still although it should be moving back and forth.
Continuity mistake: Don Rickles is assembling the .30 calibre machine gun onto its tripod prior to the action in the French village. Neither he nor his co-gunner have any visible anmmunition. The scene changes, the comes back to the .30 calibre machine gun, which is set up on its tripod and is loaded with a belt of ammunition. Where did the ammunition come from?
Continuity mistake: When the squad is crossing the cleared cornfield and encounters mines, each individual is forced to meticulously check with his knife and crawl individually to where he could follow Kelly's path. The cornfield surface all around is uniformly chewed up with moist dirt and lots of plant debris. However, when the German patrol shows up, the remaining soldiers escape along a well-worn, tamped path and the surrounding field looks dried out, smoother, and with much less plant debris.
Deliberate mistake: The German tanks in this movie are not really Tiger tanks. They are Russian T-34's made to look like Tigers. The T-34's are done up very realistically, including Zimmerit (the wavy pattern on the hull of the tiger), which was an anti-magnetic paste put on the tank.