Factual error: None of the German tanks are accurate representations of German WWII types. They are all post war US variants. ie. M47 Patton Tanks. [Still a mistake, but an elaboration: This is a common problem in depicting German tanks: few, if any, survived the war. The few museum examples wouldn't be released for movie work, and certainly WHERE, some 20 years after the war, would one find a brigade's worth of running Tiger II tanks? Never mind that Kampgruppe Pieper, which Hessler's command is loosely based on, actually used Mark IV and Panther tanks. There was one King Tiger battalion, and it was in reserve well behind KG Peiper. The M47s versus the M24 Chafees (mistakenly called "Shermans" at times) is a fairly accurate comparison of the respective sizes, firepower, and other combat capabilities of the respective tanks. Some other movies, like "Kelly's Heroes", have their "Tigers" mocked-up with sheet metal, wire mesh, and sacking over a different type of tank (in that case, T-34/85s of the Yugoslav army are mocked up as Tiger Is, a fairly decent job).]
Continuity mistake: Near the beginning, Lt. Col. Daniel Kiley is in a scout plane and flies over Col. Martin Hessler, who is in a German staff car below. Kiley tells the pilot to "rev the engine" just above the car to entice Hessler to look up at them, so he can get a good photograph of his face. The plan works, and the ground level movie camera shows Hessler looking up. When the "photo from the air" is later developed, it shows Hessler looking up from the ground level camera's perspective, eyes focused about 30 degrees behind the airplane and giving a profile of Hessler.
Trivia: Robert Shaw's character is based on Kampfgruppe Jochim Peiper of 1st SS Leibstandart Adolph Hitler, Panzer Division. Peiper was a ruthless but extremely effective officer who had learnt his trade in death on the Russian front. Peiper survived the battle and the war and although he was initially sentenced to death for his part in the Malmedy massacre his sentence was commuted. He was killed in France in 1976 when his house was firebombed in a revenge attack.
Trivia: The American uniform-disguised German troop is inspired by the actual operation "Greif" led by Otto Skorzeny. It did however not happen as in the movie; they where not dropped in parachutes but used captured jeeps. Only very few came through and even fewer had any success. Skorzeny had very little time for preparations, The shortage of men with language skills at the desired level was severe and he considered aborting the operation because several conditions of the plan had not been met. Rumours about the target of the task force were encouraged, one being that their target was Eisenhower's HQ in Paris.
Trivia: The tank models used by the German commanders at their headquarters look just like the actual King Tiger and Sherman tanks used by both sides during the late part of the war, whereas the tanks used in the film look nowhere near like actual German and American tanks used during the battle.