Factual error: Miller rigs his booby trap by attaching the wires from the bomb to a pole down which a metal runner slides, so that when the runner touches the wires it completes the circuit and detonates the bomb. The trouble is, the pole is made of steel, and steel is very conductive indeed. Miller attaches the exposed end of the wire to the pole without any insulation or gap. The circuit will actually be completed when Miller attaches the battery, and he and his booby trap will be blown sky high.
Other mistake: When Miller throws explosive into the German patrol boat's engine room it explodes in sheets of flame, etc. However, there is no damage at all to the fishing boat - no scorch marks and no debris. At least the sail should have caught fire.
Continuity mistake: In the scene where the group is climbing the cliff, even when Mallory and Stavros reach the summit and kill the German soldier, there is hard rain. However, in the next shot when they throw the German soldier by the cliff, there is no rain and the sky is clear.
Other mistake: Towards the end, when the Germans are searching for explosives around the guns, there are several Germans using metal detectors, yet they are walking along the steel rail tracks and around metal shells and ammo boxes.
Revealing mistake: In the shots taken from above, on the scene where Mallory and Stavros are climbing the cliff under hard rain, the rain falls over the back of them, not over his head. Reveals that this scene was taken in horizontal position over the floor. Not taken in vertical position.
Continuity mistake: When David Niven is at the bottom of the hoist setting the explosive charge, his hands are covered in grease as he is hiding the wires, which would complete an electrical circuit. Seconds later, when he and Gregory Peck are moving toward the guns his hands are perfectly clean. There was no time to wash his hands - or any evidence of a sink - when the Germans were feverishly trying to get into the tunnel.
Continuity mistake: When James Darren has his final shoot-out, the German officer approaching him looks unscathed, but then in the next shot his coat is full of bloody bullet holes, before they start shooting at each other.
Other mistake: When the fishing boat is stuck at the base of the cliff we see it tossing and rolling. However, when Brown is in the hold there is no movement. Also when the men are unloading their supplies the boat is obviously fixed and stationary.
Other mistake: At the beginning of the film a bomber is crashing. As this is happening another bomber is stationary in the sky.
Audio problem: At the end when they're on the small getaway boat, Irene Papas asks Anthony Quinn a question. He answers, "Yes," but his lips don't move.
Audio problem: When Maria is talking to the other woman at the ruins after she comes to, the last time she says, "Our friends," her lips don't match the words.
Other mistake: After Mallory answers the field telephone on the rocks, the German telephone operator sounds the alarm. When the alarm goes off, Germans run out and jump onto a truck. When the truck drives away it says Dodge on the back.