Nose Fuzes No. 860 Mks I and II, and No. 896 Mk I. Tail Fuzes No. 867 Mk I, No. 885 Mk I and No. 886 Mk I (Service)

Description: The Fuze No. 860 Mk II consists of a body into which is screwed a stri-ker housing and a gunpowder magazine fitted with a percussion cap. Inside the striker housing a compressed striker is retained by three retaining by three retaining balls. These balls engage a sloping shoulder on the striker and the tapered internal surface of a slee-ve surrounding the housing. The sleeve is held against axial movement, while the striker is in the cocked position, by three larger balls, which are located in three upper holes in the striker housing. These larger balls engage the parallel portion of a cone-ended arming pin, which is secured to a boss in the end of a vacuum bellows. The non-pointed end of the striker has a hole into which the pointed end of the arming pin can enter.

One end of the vacuum bellows and a stop plate form the closed end of a cylinder, which passes over the striker housing and abuts against a washer located in a cup. An arming spring is compressed between the cylinder and the fuze body. The vacuum bel-lows contain a spring, which regulates expansion or contraction of the bellows by atmos-pheric pressure.

When the fuze is unarmed, the cylinder is held down towards the magazine by an arming screw, which is screwed through an arming-vane support carried by a thin outer cover attached to the fuze body by screws.

The arming screw supports an arming vane which is mounted that it is permitted half an inch of free travel before it locks against the head of the arming screw. Two stop pins, one projecting from the arming-vane support and the other from the arming-vane hub, prevent these two parts from binding together.

The arming vane is protected against damage, premature rotation, and freezing by an arming vane cover bedded against the outer cover of the fuze. The arming-vane cover is fitted over three clips riveted to the outer cover. A vane stop, riveted to the inside of the arming-vane cover, prevents premature rotation of the arming vane due to vibration. A lug is provided on the arming vane cover for attachment to the fuze-setting control link of a bomb carrier.

Four vent holes in the outer cover permit air to escape from inside, thus relieving ex-cess pressure built up inside the fuze while falling after the arming screw has fallen away. The vent holes are covered by adhesive tape on which is written: TO BE REMO-VED AFTER FLARE IS FIXED ON CARRIER.

A safety pin is housed in the fuze body between the striker and percussion cap, so that, if the striker should be prematurely released, the safety pin will prevent its firing the cap. The safety pin is held in place by a shear wire in a groove around the fuze body and in a slot in the head of the pin. A spring, housed in the body, is compressed beneath the head of the safety pin. A clip is mounted on the shear wire and can slide along the wire.

Operation: When the fuzed weapon is dropped from the plane, the arming-vane co-ver is pulled clear and the arming vane exposed. The shear wire is broken and the spring ejects the safety pin. The arming vane then rotates freely until it becomes locked on the head of the arming screw. The screw rotates with the vane until they both fall away. The cylinder, together with the vacuum bellows, will then have been moved by the arm-ing spring so that the stop plate rests against the inner end of the setting screw. This movement of the cylinder withdraws the arming pin so that the balls engaged by the pin rest against the cone-shaped end of the pin.

As the weapon continues to fall, atmospheric pressure increases, and the vacuum bellows contracts, thus compressing the spring in the bellows and withdrawing the arm-ing pin. When the weapon reaches the predertermined barometric pressure, the arming pin will have moved up, and the balls pressed into the striker housing by the sleeve. This permits the sleeve to be cammed away from the magazine end of the fuze by the action of the striker spring, until the balls engaging the striker are freed and fall away. The stri-ker is released and is forced by its spring against the percussion cap, which fires the gunpowder magazine.

Remarks: The Nose Fuze No. 860 Mk I differs from the Mk II in that the zinc-colored section of fuze is of greater diameter than the rest of the body.

The Nose Fuze No. 896 is the same as the No. 860 Mk II, but a delay element has been introduced between the cap and the magazine. The fuze is designated either A2, A3, or A4, the figure in each case indiacting the length of delay in seconds.

The Fuze No. 867 Mk I has no arming vane but is instead fitted with a T-bar, which engages an arming fork on the standard British tail unit.

The Tail Fuze No. 885 Mk I is the same as the No. 867 Mk I, but has a 2-sec. delay.

The Tail Fuze No. 886 has a shear wire to prevent arming at low speeds, and a 1-sec. delay.

Figure 165 - Nose Fuze No. 860 Mk II

Figure 166 – Operating sequences of Nose Fuze No. 860 Mk II