The Dam Busters took out all their guns and ammo to lighten the plane due to the weight and mechanism to spin the bomb so it would skip like a stone and come to rest just before the dam wall.
A depth sensor activated and hydraulic pressure did the rest.
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“Dambusters” would employ a revolutionary new weapon – a spinning, barrel-shaped 9250 lb (4196 kg) “bouncing bomb” designed by British engineer Barnes Wallis.
The Lancaster Dam Busters had a neat, super simple and low-tech system for getting the drop altitude just right. They had two spotlights pointing down at a slight angle such that when the two beams came together on the water the altitude was just right.