It is 1940. Two pilots come out of a house - one of them has just lost his wife and family in the London Blitz, the other is an RAF Squadron Leader. The door they come out of has a modern electric bell push - a post 1965 version, white rectangular box with a round button.
During the Stuka attack on the radar station, the two Stuka radio controlled models that collide was a complete accident. It looked good so was left in the final version.