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.
Factual error: When the commandos are heading to Navarone by fishing boat, they are buzzed by the piston-engine high-wing observer plane (looks a lot like a tricycle-gear Cessna, not around in that period). As the aircraft passes it sounds like they were buzzed by a big powerful craft, like a Mustang or a Spit.