Base Detonationg Fuze Mk 3 Mod 2 (Obsolete)

Projectiles used in

Over-all length, inches

Body diameter, inches

Head diameter, inches

Weight, pounds

Threaded lenght, inches

Threads

Material

Description: This fuze consists of two major parts: (1) a tracer head, threaded ex-ternally to screw into the base of the projectile and containing the tracer primer and py-rotechnic components; (2) the fuze body, which houses the Semple firing pin and firing-pin housing, the primer detonator assembly, the centrifugal half-block, the safety coil, and the booster.

In the unarmed position, the firing pin, which is pivoted in its housing, is held offset from the primer by a pair of centrifugal detents. These detents are housed in the firing-pin housing and engage the hole in the weighted end of the firing pin. Also, in the unarm-ed position, the detonator is separated from the booster by a pair of centrifugal half-blocks. Each half-block is TNT stemmed to form a booster lead-in, but the stemmed por-tions of the two half-blocks are out of alignment in the unarmed position, providing a safety interruption in the explosive train. Additional safety is provided by encasing the detonator in a small expansion chamber surrounded by a safety coil. Accidental explosion of the detonator will expend its forces against the safety coil and will not fire the stem-med half-blocks or the booster.

Operation: When the projectile is fired, the tracer primer functions and ignites the tracer element in the base of the fuze. Centrifugal force causes the centrifugal detents and the centrifugal half-blocks to move outward against their springs. This aligns the booster lead-ins in the half-blocks and unlocks the pivoted firing pin. Since the firing pin is heavily weighted on its lower end, centrifugal force rotates it about its pivot and brings it point into alignment with the primer. On impact, the firing-pin housing moves forward against the anti-creep spring, bringing the firing pin against the primer, which, in turn, fires the detonator. The flash from the detonator initiates the stemmed lead-ins in the half-blocks, the booster charge, and finally the projectile.

Remarks: Because of the shape of the striker, the force of the initial acceleration prevents centrifugal action from alignment the firing pin until after the projectile has left the bore of the gun. When acceleration ceases, centrifugal force revolves the pivoted firing pin to the armed position.

Figure 102. Base Detonating Fuze Mk 3 Mod 2