Re: 1969 film
Another great war movie - The Dambusters....I read that they couldn't get enough aircraft, and so they used copies of the same strip of film, overlayed on each other to give the impression of more aircraft in flying sequences. Apparently, if you look carefully, you can see some Lancasters flying backwards.
This is the same film that couldn't film any actual post-dam-bust footage, so used some existing newsreel footage of flooding in the deep south of the USA. Again, if you look carefully, the shots of the flooded Ruhr valley feature negro farmers.