Mk 31 and Mk 36

Rockets uses in

Functioning

Body diameter, inches

Over-all length, inches

4.68

General: The Navy Rocket Base Fuze Mk 31 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-stabilized rockets. The fuze is designed for instantaneous action on impact. It is shipped installed in the base of the rocket body.

Description: The fuze is composed of two major parts: the fuze body and the noze cap. The body contains the auxiliary detonator plunger, the detonator plunger, the deto-nator-plunger detents, the anti-creep spring assembly, and the firing train. The auxiliary detonator 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 move, and the inner cup is crimped overt 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 and firing-pin detents. The sensitive firing pin is held in place by two stakes, but is referred to as a "floating" firing pin, since it can move downward sligthly. 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 set-back 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 then completely armed. The detonator plunger is prevented from moving forward 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 sesitive 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 primer, and the flash sets off the detonator and booster elements.

Remarks: The Base Fuze Mk 36 differs from the Mk 31 only in that it has a 0.01 se-cond delay element housed in the space which is the flash channel in the Mk 31.

Figure 161. Navy Base Fuzes (Rocket) Mk 31 and Mk 36