Spinning? Top of my head - Back-spin was to be initiated 10 minutes prior to arrival at a target, and was imparted via a belt driven by a Vickers Jassey hydraulic motor mounted forward of the bomb's starboard side, the motor itself being powered by the hydraulic system normally intended for the upper gun turret, which had been removed as part of the aircraft's modification.
Wiki really.
Bouncing bomb - Wikipedia, the free encyclopedia