Metcalf takes off in a Wellington aircraft and parachutes from a Whitley.
When RAF bombers are shown flying to attack the U Boat base, they are a flight of Blenheim's flying in daylight, not night time as the film depicts. When the bombers start bombing it is now night time and they are now Wellingtons.
When the escaping German commander of the town shoots the Norwegian police chief, the pistol is plainly seen beside the man's body pointing towards the wall of the room, not into the man's abdomen, so when he pulls the trigger, the bullet would hit the wall, not the policeman. The German commander turns takes a couple of steps and slumps forward in advance if the police chief shooting him in the back.
At the end of the film when the soldiers and civilians board the landing craft, one grabs the post of the craft allowing it to move from side to side; this would not happen if it was metal. You can clearly see it is a prop made of wood.
There is some very hurried stock footage run at the wrong speed, of German U-boats during the attack on Alstad's boat.
In the opening credits, there is a spelling error 'Norweigan', which should be 'Norwegian'.
When Metcalfe is being helped by the Norwegian baker and his wife and being fed in their kitchen, there is a portrait of George Washington on the kitchen wall.