
Just one minor correction though, they were used on ALL types of bomb, not just those stated. Indeed, some had more than one attached, like the 4,000lb blockbuster which had, if I remember correctly, 5 in the base !
This is how they worked.....
The 'pistol' was screwed into the base of the bomb and a vane attached to the fork in the rear. When the bomb dropped from the plane, the wind would spin the vane and therefore undo the brass fork. Once totally unwound, the firing pin was then 'free floating'. As the bomb hit the ground, the firing pin would shoot forward under the speed of the impact and hit against the detonator within the bomb, thus setting the detonator off.
Hope that helps

RRPG
PS They were also used in American ordnance as well. It is quite common to find them on USAAF and RAF airbases.