USNBD, Rockets and Fuzes; Nose Fuze Mk 140

U.S.N.B.D. - ROCKETS AND FUZES

ROCKET FUZES

ROCKET USED IN	7.2" Rocket Ammunition	U.S. NAVY NOSE FUZE
	Shipboard (Mousetrap) and
	7.2" Projector Charge Am-	Mk 140
	munition (Hedgehog)
FUNCTIONING	By inertia upon impact
	with solid object after
	armed by hydrostatic pres-	Hydrostatic Arming, Impact Firing
	sure.	Rocket Propellant
ARMED CONDITION	No external indication
FUZES USED WITH	None
ARMING TIME	Arms under static pressure
	of approximately 30 feet of water. At the high velocity with
	which the rocket strikes the water dynamic pressure is built
	on the head and it arms at depths from 8 to 15 feet.
MAX. BODY DIAMETER	2.7 in
OVERALL LENGTH	4.5 in

GENERAL:

This fuze was developed and issued to replace the Mk 131 and 136 in the 7.2" Rock-et Ammunition Shipboard (Mousetrap) and 7.2" Projector Charge Ammunition (Hedge-hog) It arms by hydrostatic pressure and has safety features which prvent it from firing either on setback or impact wiht the water. Its sidewise sensitivity is 1/6 to 1/4 of the nose sensitivity, and a glancing blow permits the fuze to function. Orders have been is-sued that fuze is not to be used and it will be recalled. The fuze can be used by blimps in 7.2" heads without the motor, when dropped as bombs.

OPERATION:

When rocket is fired, the arming wire is pulled. On setback, the safety ring is forced down over the upper hooks on the two ball cranks, preventing then force from spread-ing 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 ball cranks, thus preventing the ball 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 formely received the arming wire. After reaching a depth of from 8 to 15 feet, the pressure of the water will pop the phosphor-bronze diaphragm, which presses down on the inner ends of the ball cranks. Since the ball cranks are pivoted about pivot pin, they swing clear of the detonator slider, which is forced over to the armed position by two springs, and locked there by a spring-load-ed detent. On impact with a submarine or other hard surface, the firing ring is forced by inertia gainst 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 sideway, camming the firing ring forward, releasing the locking balls and firing the fuze.