ROCKET USED IN

FUNCTIONING

ARMED CONDITION

FUZES USED WITH

ARMING TIME

MAX. BODY DIAMETER

OVERALL LENGTH

5-1/2"

GENERAL:

The fuze head screws into an adapter fixed in the base of the rocket body and the gasket and luting on the threads make a gas tight seal. The top of the fuze is exposed to the front end of the rocket motor. The Mk 146-1 differs in that it has a more sensi-tive firing train. These fuzes are being replaced in the 5.0" Rocket by the Mk 157-0 fuze. The Mk 146-1 being replaced in the 7.2" Demolition Rocket Mk 10-1 head by the Mk 161-0.

The fuze is shipped in the base of the rocket head and is not to be removed.

OPERATION:

When the rocket is fired, gas under considerable pressure from the rocket motor passes through the inlet screen underneath the inlet screw and enters the pressure chamber. As the gas pressure build up, the diaphragm bears against the arming plunger, breaking the shear wire and forcing the arming plunger inward. The locking ball, which is preventing the rearward movement of the striker block, is forced over by the pressure of the spring-loaded striker block into the narrow portion of the arming plunger. The striker spring forces the striker block rearward, retracting the firing pin from the deto-nator shutter. The shutter is still prevented from moving across the fuze by action of its spring until after deceleration begins, since the force of setback thrusts the shutter back and causes the shutter locking pin to engage in a recess in the firing pin guide. After burning of the propellant ceases and deceleration begins, the shutter rides for-ward, disengaging the locking pin from the guide. The shutter spring forces the shutter across the shutter cavity, where it is locked in the armed position by a detent which is housed in the firing pin guide and which engages a recess in the shutter. On impact, inertia drives the striker block forward against its spring, the firing pin striking the deto-nator.

REMARKS:

(1) A delay of .02 sec. can be incorporated in the detonator to achieve greater pe-netration when used in high velocity aircraft rockets. (See Mk 157, page 101).

(2) The later models of this fuze have undergone the follwing modifications:

a. The inlet shield has been modified. The two outside "legs" are slightly longer than the flat base of the shield so that the inlet screen will not be crushed when the inlet screw is tightened.

b. The ball retaining plug, staked in place has replaced the screw plug.

c. A safety pin has been fitted below the spacer sleeve to facilitate assembly operations.

d. The detonator shutter has taken on an oval shape, eliminating the former squared corners.

e. The latest lots of Mk 146 fuzes have been further altered to increases the overall sensitivity of the fuze by using (1) a weaker creep spring, (2) a more sensitive primer, and (3) a more tapered firing point.