|Type 90 "Nose Initiator" - Navy|
The Type 90 Nose Fuze - U.S. Designation A-1(b) - used on the Type 99 No.3 Mk.3 HE/Incendiary Bomb (70lbs).
On release from the aircraft, the safety fork is withdrawn and the vane assembly rotates about five times, unscrewing the anvil up and off the striker spindle. (The vanes stay attached.)
On impact, the anvil slams the spindle down, breaking the shear wire causing the firing pin to strike the primer.