Anachronisms: Near the end of the movie, an electric locomotive is visible. The model was not manufactured until the late 1960s.
Continuity: During the film, and especially the mission to infiltrate the German supply dump, none of the commandos, including Major Mallory can understand German. This is especially clear when Leskovar insists he must accompany the team to the dump as only he speaks German and, later, when the team is discussing Leskovar's encounter with the German Sergeant in the train car. All of this ignores the fact that this film is a sequel to "The Guns of Navarone" in which Mallory is specifically chosen for the mission because he speaks "German like a German." Alistair MacLean's original stories also support this fact.
Continuity: Weaver kills the German soldier who is about to shoot Miller, who is hanging in a tree by his parachute, by throwing a switchblade into his back. Besides the fact that switchblades are poorly balanced and utterly unsuitable for throwing, Weaver joined the team after escaping from the custody of several MPs, who would presumably have disarmed him upon his arrest, leading to the question of where the knife came from.
Continuity: When Force 10 is taken to the "partisan" camp and the so-called "partisans" reveal themselves to be Chetniks (German allies), they turn their caps around to hide the communist red stars they were wearing as a disguise to reveal their Chetnik insignia, including the group who met Force 10 initially. However, none of those Chetniks had any insignia on the backs of their caps at the first rendezvous.
Continuity: When the diversion is created at the dam, and German trucks leave to investigate, dawn is breaking, but a few seconds later when the cameras switch back to the dam, its still dark.
Anachronisms: At the beginning, when Mallory and Miller are being briefed, we see a map with the Post-War Flag of Yugoslavia displayed on it.
Factual errors: A German soldier is seen shooting a Mauser rifle with the bolt handle on the left side of the rifle. All Mauser military rifles had the bolt handle on the right side which would indicate that the film had been reversed.
Factual errors: The tanks used by the German army when crossing the bridge are actually the T-34 tanks manufactured and used in WWII by the Soviet Union that fought AGAINST the Germans.
Continuity: The exterior shot of Mallory and Barnsby entering the dam shows Barnsby pulling the door outward. The interior shot shows him pushing the door in.
Plot holes: With a fairly large dam 2 miles away, why do the Germans need the bridge to get their tanks across? They could just cross on the dam.