The scene where the helicopter lands and then takes off again from a flat wagon on a train traveling at over 40mph had never been attempt before this film and had to be repeated 15 times over two days before the directors were satisfied that it looked just right.
When Jim Ferguson first visits Colonel Raymond at Tower Bridge, Raymond hands Ferguson an antiquated 'Celebrity Dinners' card. When Raymond passes Jim the card, it is in a plastic sleeve, then the camera shows the card in detail without the sleeve, and then it returns when Jim hands it back.