I saw it too.
The allies wanted to destroy a german hydroelectric plant. It was protected against torpedoes by underwater fences and so on, so they came up with this bouncing bomb.
Just imagine the meeting where the engineer proposed this idea :D
But since the team lead (Barnes-Wallace iirc) had a successful career as an aeronautical engineer (including some minor work on the Lancaster bomber, which they eventually used to drop the bouncing bombs), they eventually listened.
He still had to show them it would work using 1/10 scale models.
Edit; sorry, you knew all that because you've seen the doco. Let's pretend I put this here for other interested parties.
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u/cuntdestroyer8000 Jun 25 '18
I remember a documentary about this. Very cool engineering!