ROCKETS USED IN

FUNCTIONING

ARMED CONDITION

FUZES USED WITH

ARMED SPEED

MAX. BODY DIAMETER

OVERALL LENGTH

GENERAL:

The Mk 31 Rocket base fuze is identical to the Navy Base Detonating Projectile fuze, Mk 31. This fuze is armed by centrifugal force and thus can only be used in spin-stabi-lized rockets. The fuze is designed for instantaneous action on impact. The fuze is shipped installed in the base of the rocket body.

DESCRIPTION:

The fuze is composed of two major parts: the fuze body and the nose cap. The body contains the auxiliary detonator plunger, the detonator plunger, the detonator plunger detents, the anti-creep spring assembly and the firing train. The auxiliary deto-nator plunger is surrounded by twenty ball bearings and bears against the bottom of the detonator plunger. Fitted over the top of the detonator plunger is the anti-creep spring assembly consisting of an inner and outer cup separated by an anti-creep spring. The outer cup will not have and the inner cup is crimped over the top of the detonator plunger and held in position by the sensitive primer holder. The firing train consists of the sensitive primer, plunger firing pin, secondary primer, detonator, and booster lead-ins and lead-outs which are out of line in the unarmed position.

The nose cap, which is secured to the end of the body by a threaded joint houses the sensitive firing pin is held in place by two stakes, but is refered to as a "floating" firing pin since it can move downward slightly. Ninety degrees removed from the two detents are two holes in the nose cap. A locking pin is provided to lock the nose cap in position.

OPERATION:

The force of setback causes the sensitive firing pin to move back on the firing pin detents and hold them in by friction. When the motor burns out, creep causes the firing pin to move forward and release the detents. Centrifugal force will move both sets of detents outward against their springs and the fuze is than completely armed. The deto-nator plunger is prevented from moving on creep because of the anti-creep spring, but on impact the auxiliary plunger acting as an inertia weight pushes the detonator plunger forward. This action moves the inner cup forward thus compressing the anti-creep spring and brings the booster lead-ins and lead-outs in line. The sensitive primer in the top of the detonator plunger is carried on to the sensitive firing pin and the explosion of the sensitive primer accomplishes two things;

1. The gases resulting from the explosion pass through the port holes on the side of the primer container and build up a high pressure expanding that part of the cup which is adjacent to the holes in the nose cap. This action locks the detonator plunger in the fired position and keeps the firing train lined up.

2. The shear wire that has been holding up the secondary firing pin is broken and the secondary firing pin is driven down into the secondary plunger and the flash sets off the detonator and booster elements.