PIBD, M509A1, M509A2, M509A1E2, M509A2E1
Point initiating, base detonating type Fuze M509A1 is used with fin stabilized HEAT projectiles in calibers from 76mm to 120mm.
The fuze is essentially an aluminum housing containing a spring loaded rotor and an electrically fired Detonator M48. The rotor is the arming mechanism and houses the detonator. In the unarmed position, the rotor is restrained by three metal leaves, so arranged as to be displaced sequentially by setback. The power source is a polarized piezoelectric ceramic disk (not shown) in the nose of the projectile connected by a wire lead to the fuze. When the rotor is in the armed position, the detonator is aligned with a booster lead charge and booster charge in the nose end of the fuze.