Mk 146 and Mk 146 Mod 1

Rockets uses in

Functioning

Fuzed used with

Arming Time

Body diameter, inches

Over-all length, inches

5.50

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 Base Fuze Mk 146 Mod 1 differs in that it has a more sensitive firing train. These fuzes are being replaced in the 5.0-inch rocket by the Base Fuze Mk 157 Mod 0. The Base Fuze Mk 146 Mod 1 is being replaced in the 7.2-inch Demolition Rocket Head Mk 10 Mod 1 by the Mk 161 Mod 0. The fuze is shipped assembled 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 pres-sure chamber. As the gas pressure builds 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 de-tonator shutter. The shutter is still prevented from moving across the fuze by action of its spring until after deceleration begins, since the force of set-back thrusts the shutter back and causes the shutter lokcing pin to engage in a recess in the firing-pin guide. After burning of the propellant ceases and deceleration begins, the shutter rides forward, 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 dri-ves the striker block forward against its spring, the firing pin striking the detonator.

Remarks: A few of the early experimental models incorporated a delay of 0.02 second to allow penetration. The Base Fuze Mk 157 was developed from these. The later models of this fuze have undergone the following modifications:

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

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

3. A safety pin has been fitted below the spacer sleeve to facilities assemby operati-ons.

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

5. The latest lots of the Base Fuzes Mk 146 have been further altered to increase the over-all sensitivity of the fuze by using a weaker creep spring, a more sensitive primer, and a more tapered firing point.