Mk 131 Mods 0-6, Mk 136 Mods 0-10

Rocket uses in

Functioning

Identification

Arming Time

Vane span, inches

Body diameter, inches

Over-all length (without booster), inches

7.2

General: These two fuzes are identical, except that the Nose Fuze Mk 136 has a shear wire through the set-back collar. Both fuzes were to be replaced by the Nose Fuze Mk 140; however this fuze is being recalled from the field. The Nose Fuze Mk 131 has been replaced by the Mk 156 and the Mk 136 has been replaced by the Mk 158 Mod 0.

Operation: The safety pin is removed when the rocket is loaded on the launcher, lea-ving the vanes secured by the set-back collar, which has a leaf spring holding it up by pressure against the locking pins. On firing, the set-back collar moves back (breaking the shear wire in the Mk 136), freeing the locking pins from the groove in the collar. On im-pact with water, the force on the vanes cause a torque sufficient to shear the vertical shear wire holding the vane cup to the neck of the fuze. The vanes are free to rotate, unthreading the spindle through the neck of the fuze body. As the spindle draws back from the inertia weight, the spring under the firing sleeve force the sleeve and inertia weight up. Since the firing pin is locked to the firing sleeve by three locking balls, the firing pin and its spring, cocked against a collar on the firing pin, rise with the sleeve and inertia weight. As the sleeve clears the four spring-loaded detents in the fuze body just above the firing-pin guide, the detents spring out under the sleeve. After approximately four vane rotations, the firing pin will have been raised by the sleeve sufficiently to clear the shutter cavity, allowing the spring-loaded detonator shutter to move over into the armed position with the detonator lined up with the firing pin and booster lead-in. The spindle continues to rise until the washer to which it is keyed engages a groove in the underside of the fuze neck. The inertia weight, sleeve, and firing pin cease rising when the sleeve engages the retaining ring after rising approximately ¼ inch. On contact with a target, the three locking balls are forced inward, as inertia causes the weight to move forward on normal impact or laterally on oblique impact. As the weight moves clear, the locking balls are forced outward by the beveled edge of the spring-loaded striker, which is then free to be driven into the detonator.

Remarks: The detents in the fuze body, which spring out under the sleeve, are pro-vided in order to allow the spindle to be screwed back down from the armed position without danger of forcing the striker into the detonator. In view of the fact that the inertia piece may be insercurely lodged over the striker spindle, this procedure is not re-commended on any rocket that has once been fired.

Do not remove these fuzes from a projcetile with any tool other than the span-ner which is issued with the fuze. Separation of the two parts of the body arms the fuze.

Difference in Mods for the Mk 131 and Mk 136 were minor distinctions, some being se-parate contracts.

Some lots of the Mk 136 will have small-vane shear wires.

Figure 149. Navy Nose Fuze (Rocket) Mk 131 Type