Goofs

Right after the letter from Hitler is read, it is remarked that the future Fourth Reich are all sitting in train car #2420. But a moment later, as the train starts to leave, the camera pans down so we can see the number on the car - it is 2024. At the end of the film, the train car is shown again and the number has changed to 2420.

Major Wright is wearing silver oak leafs which is the rank of Lt. Col.

A US WWII M1 steel helmet consists of two major parts, the outer steel shell which affords some ballistic and fragmentation protection together with the inner lightweight (non-steel) helmet liner. Telly Savalas wears the helmet liner without the steel shell - that would never occur in combat. It is a common Hollywood war movie cheat to reduce fatigue and strain on the actor's head and necks.

The helmets of the Bulgarian soldiers, killed on the bridge had the colors in wrong order. White on top, green in middle, red on the bottom. The red and green were switched.

Although Lieutenant Carol Campbell possessed extensive knowledge of various European languages and customs. She would have never been allowed to join the mission. Women in the U.S. Military at the time of World War Two were not allowed to serve in combat.

At least allied 17 soldiers and one partisan jump from the moving train in the final battle. Counting the soldier killed in the locomotive and the two deaths earlier in the movie there's clearly more soldiers jumping than there should be.

In the final battle some mortar explosions explode close enough the allied soldiers to count as direct hits but cause no damage to them. German soldiers on the other hand seem to die when no explosions occur nearby,

Throughout the movie, members of the Dirty Dozen are wearing web belts from the M1956 series of gear that didn't exist until 1956 and wasn't implemented until the Vietnam War.

As they are panning over dead German soldiers they show two, one with leg bent back in foreground who takes a breath and moves his lips but is supposed to be dead.