When the goods train is shunting in the yard, it consists of wagons (open) and vans (closed), clearly of British outline; one vehicle has a number panel from 1970's British Rail. After the saboteurs are carried away in this train, it is seen to emerge from a tunnel, consisting of an electric locomotive (see elsewhere: anachronism), pulling only a train of continental outline vans.
When Mallory and Barnsby return to the Chetnik camp to free their comrades Mallory addresses Schroeder's clerk as Sergeant. The clerk is wearing corporal's chevrons. Sergeants in the German army in WWII wore their rank insignia on their shoulder tabs.
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.
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.
When Sgt Weaver gets out of the MP truck he removes his combat jacket and is just wearing a shirt, when he boards the Lancaster he is still just wearing a shirt. He's still only wearing a shirt while on the plane. However once he's on the ground after jumping, he is wearing a roll neck woolen jumper and a Denison Smock. There isn't time for him to take the clothing from one of the dead soldiers on the plane.
When the teams Lancaster is under attack by German fighters there is a brief closeup shot of the fighter's machine guns firing. Those machine guns were arraigned in a configuration (same config as the Hawker Hurricane, four side by side) that no German fighter ever had during the war. The ME109 carried several guns and cannons in various configurations during the war, but never as depicted in the movie.
Continuity with "The Guns of Navarone": Mallory and Miller are shown at the beginning of this film being picked up by the Royal Navy ships passing Navarone. In that scene, they are wearing German uniform jackets. They discarded those jackets while they were in the gun cave at the end of "The Guns of Navarone".
In the long shots of the bridge we can see several short arches going down a hill leading to one long arch. In the close-up shots of the bridge (clearly a model) being destroyed by the river, the bridge's arches are of equal size and spacing, and sit on level ground.
When the German vehicle commander's head is sliced off by the wire, blood gushes out of his neck all over his uniform, but when the Force 10 soldiers remove his uniform immediately afterward, it's clean with no bloody mess.
Just before the German vehicle commander's head is sliced off by the wire, he is shown in his vehicle with two German soldiers in a position behind him with their head and shoulders above the vehicle turret except they are facing to the rear. When his head is sliced off and immediately afterward when the vehicle runs off the road, those two soldiers are missing.
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.
The first screen shot after the initial briefing is of a sign, Termoli Air Base, identifying two separate commands who occupy it. One is HQ 462 Sqdn RAF, the other HQ 17 Corp USAF. The United States Air Force did not exist until after the war, in 1947. Prior to that, it was the United States Army Air Corps, (USAAC), a division of the US Army.
Whilst stealing explosives from the railway yard the team jump into a railway carriage that is not only from the UK but form the UK Ministry of Defence. One of the carriages has the the abbreviation PSTO(N) written on it. These are British Ministry of Defence (MOD) carriages, used in MOD Armament Depots, specifically the Navy. PSTO(N) stands for Principle Supply and Transport Officer (Navy).
The goof items below may give away important plot points.
Just before the dam cracks and begins spewing water, the camera shows a panoramic view of the dam with a reservoir at the bottom is visibly green water. When the water initially breaks through, the camera shows a reservoir of brown muddy water, clearly not the same real dam, just a mock-up.