Mk 140 (Recalled)

Rocket uses in

Functioning

Arming time

Body diameter, inches

Over-all length, inches

4.5

General: This fuze was developed and issued to replace the Nose Fuzes Mks 131 and 136 in the 7.2-inch Mousetrap and Hedgehog. It arms by hydrostatic pressure and has safety features which prevent it from firing either on set-back or on impact with the wa-ter. Its sidewise sensitivity is 1/6 to 1/4 of the nose sensitivity, and a glancing blow per-mits the fuze to function. Orders have been issued that this fuze is not to be used, and it will be recalled. The fuze can be used by blimps in 7.2-inch heads with the inert motor, when dropped as bombs.

Operation: When the rocket is fired, the arming wire is pulled. On set-back, the safe-ty ring is forced down over the upper hooks on the two bell cranks, preventing them from spreading out and releasing the detonator slider. On impact with the water, the firing ring slips down a slight amount and engages the lower hooks on the bell cranks, thus preven-ting the bell cranks from spreading to release the detonator slider on water impact; the hooks on the crank also prevent the firing ring from dropping free of the locking balls. As the rocket travels through the water, water enters the ports in the protective cap and through the holes in the nose plug which formerly received the arming wire. After reach-ing a depth of from 8 to 15 feet, the pressure of the water will invert the phosphor-bron-ze diaphragm, which presses down on the inner ends of the bell cranks. Since the bell cranks are pivoted about pivot pins, they swing clear of the detonator slider, which is forced over to the armed position by two springs, and locked there by a spring-loaded detent. On impact with a hard surface, the firing ring is forced by inertia against its two firing-ring springs, which are coiled around two guide pins. This action of the firing ring frees the locking balls, which are forced outward by the spring-loaded striker, which is then driven into the detonator. A glancing blow causes the loosely fitting striker ring to move sidewise, camming the firing ring forward, releasing the locking balls and firing the fuze.

Figure 154. Navy Nose Fuze (Rocket) Mk 141 Mod 0