Continuity mistake: In a scene in a town on the rooftops as the British fight the Nazis, we see that the townsfolk were truly ahead of their times as they nearly all have television antennas.
Continuity mistake: There is a close-up of a parachutist's boot as he leaves the aircraft. It is a DMS boot. DMS boots were not issued to the army until much, much later. Late sixties, early seventies as I recall.
Continuity mistake: Halfway through the movie, James Caan drives his jeep to escape Nazi brigades and brings his wounded comrade to the hospital. He is wearing full dress, with jacket. After he holds the doctor at gunpoint to "check" his friend, the scene switches outside where he is smoking a cigarette without the jacket, then flashes back with him wearing the jacket.
Factual error: The shots of an air-strike on German artillery positions during the first armour encounter have used the Harvard aircraft (also known as T-6 Texans). However these were only used as advanced trainers by the Allied forces and never used in combat in the European theatre. One could assume from the theatrical paint jobs that the production team were attempting to disguise them as P47 Thunderbolts.
Factual error: The shot of a tank wreck being pushed off the road following the first tank battle shows a Chaffee light tank, which was only used by the Americans and not the British. Anyway, it was first used in Europe in November 1944 after Operation Market Garden took place.
Factual error: The C-47s are shown with steel collapsible chocks that were in use in the RAF from about 1960 onwards. In WWII all chocks were made of wood.
Continuity mistake: When they're building the Bailey bridge to replace the destroyed Son bridge, work continues into the night. Cut to scene of a soldier waiting for them to complete the bridge - in daylight. Cut back to the continuing work on the bridge - it's dark again.
Continuity mistake: After the scene where a British soldier is killed trying to recover supplies, a C-47 is seen crashing with a smoking engine. After the crash, look carefully at the explosion and you can see the airplane winging away.
Factual error: The German tanks in the film are Leopard 1 tanks, which were made about 20 years later. Although the turret and the cannon are changed and there are different skirts, the Leopard is very recognizable by it's specific exhaust grill and back.
Factual error: The Waffen SS soldiers throughout the movie are wearing the wrong uniforms. By 1944, most Waffen SS soldiers should be wearing half or full camouflage. Their helmets also shouldn't have the swastika on it, and many should also have been camouflaged.
Factual error: In the conference between Feldmarshalls Rundstedt and Model, they decide to move the 2nd SS Panzer Division, under Bittrich, to Arnhem to refit before fighting Patton's anticipated attack. Actually, it was Bittrich's II SS Panzer Korps (with the 9th and 10th SS Panzer Divisions) that were at Arnhem. The 2nd SS Panzer Division did not fight at Arnhem.
Factual error: When the tank corps is shown before leaving, the village is refered to as Leopoldsville. It was in fact the Belgian village of Leopoldsburg. It's shown on the map as Bourg Leopold (which is the correct French name). Leopoldville was the capital of the Belgian Congo which is now called Kinshasa.
Factual error: In many of the scenes, German Mauser rifles do not have cleaning rods. However, judging from archive footage, almost all Mauser rifles used by the Germans during World War II had cleaning rods attached. Many weapons dealers sell World War II surplus rifles without cleaning rods because they are welded into the barrel as part of the deactivation process, hence why they're missing. Still a mistake though.