In the film of the Battle of Britain, the aircraft which crashed into the sea were models which were released from helicopters as underslung loads. One of the He111s is seen crashing into the sea with the long suspension wire trailing behind it. This is because the model became unstable and the helicopter pilot emergency released it.
Now the film producers were faced with a problem in that they didn't want to build a new model, so they included a scene where some control cables get shot through to attempt to explain the trailing wire!