14.20 into the movie the trawler taking them across the channel is fitted with a modern compact marine radar unit on the rear mast.
Colonel Preston refers to the transport plane sent to pick up the commandos as a "C-47". They were known as "Dakotas" in RAF service and no Brit ever called them C-47s.
During a firefight between German soldiers and partisans, one of the partisans pulls open the main hatch on top of a German armored vehicle and fires two shots from his automatic weapon into the vehicle, implicitly killing the crew.
The point of having armored vehicles is to protect the crew from events such as this, which is why the hatches latch on the inside, so the partisan would not have been able to open it.
USMC General wearing Presidential Unit Citation Ribbon over wrong pocket - should be over right pocket. Plus, USMC conducting clandestine missions in Europe? Would have been SOE or OSS.
British sniper using a fantasy No. 1 MkIII sniper rifle.
29 minutes into the film the US officer tells a character he is from the US Marine Corps, but he pronounces it 'marine corpse'.
The way the team comes ashore and hides the boat and moves over open landscape is not how a team on a secret mission would behave. Crossing right over a road and then walking over a open field leaving clearly visible footprints for any German troops to spot.
Colonel Preston wears the ribbons of the General Service Medal, 1962; the South Atlantic Medal (Falklands War) 1982; the Gulf War, 1991; The 5 year service medal (aka the Queen's Golden Jubilee Medal), 2002; and the Accumulated Campaign Service Medal (1994). On the upside, they are in the correct order.
The film is set in 1943. In the closing scene a picture showing the raising of the flag at Iwo Jima in 1945 is shown.
The RAF pilot is wearing a Senior Aircraftman's uniform with a 3-bladed prop on the sleeve. This is a junior rank, equivalent to a "senior" private, which didn't even exist in the RAF in WW2. It was created in 1st January 1951 and they're not pilots.
Dr Fabien and his family is afraid of being killed when he finishes his research project. But clearly the Germans would not kill a scientist with knowledge on how to make an atomic bomb.
The hairstyle of Kaminski is clearly modern and would not be common in the 1940's style period.