Tail Fuze No. 862 Mks I and II (Service)

Description: The fuze consists of an upper portion housing a water chamber with six water entry ports located in its side walls. This upper portion is sealed from the lower fuze body by a rubber diaphragm, which bears downward against the top of the striker. The striker is held in the raised position by two striker levers. One end of each lever en-gages a groove in the striker. The opposite end is pivoted in a spring-loaded lever block, which rides in a horizontal keyway. A detonator chamber housing a detonator shutter is located below and at right angles to the striker. A groove, in which rides the end of the striker, is cut in the upper side of the detonator shutter. In the unarmed condition the detonator shutter is held out of line with the striker by a safety wire. A shutter bellows is located on one end of the shutter, and a shutter spring on the other end. This spring re-sists the force of water pressure exerted on the shutter bellows and acts as the delay arming feature of the fuze. The lower part of the fuze body and the upper part of the magazine are threaded for insertion into the bomb. A rubber sealing ring and a locking ring are screwed onto these threads.

Operation: This fuze is designed so that it will not function or arm, except on water travel. Impact with a hard surface will cause a spring-loaded detent located above the detonator shutter to move down against its spring and lock the detonator shutter out of line with the striker. The striker levers are prevented from snapping the striker past dead center on hard surface impact by a shoulder on the detonator shutter. Upon the termi-nator of the force of inertia after such impact, the spring-loaded lever blocks and levers return the striker to its raised position.

As the fuze enters the water, water flows in the entry ports in the water chamber and exerts pressure on the rubber diaphragm. At the same time pressure is exerted on the shutter bellows. Pressure on the rubber diaphragm forces the striker down, moving the levers downward and the lever blocks outward against their springs. When the levers have passed dead center, the springs behind the lever blocks force the blocks inward, and the levers then snap the striker down into the detonator. The fuze will fire only after water pressure on the shutter bellows has aligned the detonator with the striker by com-pressing the shutter spring.

Remarks: An anti-countermining chamber in the fuze is designed to prevent the hy-drostatic fuze from functioning from blast pressure caused by the explosion of another bomb nearby. A mushroom valve in the top of the chamber is closed by the sudden in-crease in hydrostatic pressure caused by such an explosion. When this sudden pressure passes, however, the valve opens again, and normal water pressure is allowed to exert its force against the fuze.

The fuze is set to explode at a depth of 30 feet of water. This setting cannot be al-tered.

Figure 167 - Tail Fuze No. 862