Tail Fuze No. 880 Mks I and II (Service)

Description: The Fuze No. 880 Mk II consists of a brass body, bored centrally to house a striker guide, which is located between a shoulder at the top of the striker guide and the top of the shutter holder. The shutter holder is of machined brass, and is threa-ded into the bottom of the fuze body. It contains a spring-loaded detonator shutter.

The striker guide contains a striker pellet under a double spring load from the two striker springs. An annular groove in the pellet is engaged by three retaining balls, loca-ted in holes in the striker guide and prevented from moving outward by the walls of the shutter holder. Beneath the striker pellet, and loosely fitted to it, is a striker block and striker. A lead delay wire passes through the striker block and the striker guide. A hori-zontal channel bored in the top of the striker guide contains two spring-loaded locking detents. In the unarmed position, these detens bear against the  walls of the fuze body.

The striker guide is held compressed against its spring by an arming pin and by the vertical arming detent. The vertical arming detent in turn, is held in position by the end of the horizontal arming detent. The horizontal arming detent contains an inertia pin, which engages a hole in the top of the fuze body, preventing the horizontal detent from moving.

Safety during shipment and storage is provided by a threaded safety screw in the top of the fuze body, which prevents accidental removal of the arming pin. In addition, the end of the striker in the unarmed position fits into a blind hole in the detonator shutter and holds the detonator out of alignment.

Operation: The safety screw is removed manually when the bomb is loaded into its cluster and the arming pin is withdrawn by the parachute shrouds as the parachute opens. The striker guide now is held depressed against its spring only by the series of arming detents.

On impact, the inertia pin in the horizontal arming detent moves downward against its spring, and the horizontal detent is allowed to be forced over the vertical arming detent, which is pushed upward by the striker guide and spring. When the striker guide rises, the two locking detents are forced into the enlarged recess in the top of the fuze body, firm-ly locking the striker guide in the raised position.

Simultaneously, the retaining balls are freed, and the spring-loaded striker pellet is forced against the striker block. The striker has been removed from the detonator shut-ter, which is now caused by its spring to align the detonator with the striker.

The entire force of the twin striker springs now bears against the delay wire, which eventually shears and allows the striker to pierce the detonator, initiating the bomb.

Remarks: The Fuze No. 880 is a fatigue-type long-delay fuze with delay time desig-ned to vary from ½ min. to 6 hr. at 50° F. The designed delay time is set during the ma-nufacture of the fuze and cannot the altered. The nominal delay time cannot be ascer-tained from the external appearance of the fuze. At temperatures higher or lower than 50° F., the delay times will vary considerably from those for which the fuzes were desig-ned. At below freezing temperatures the fuze has been known to delay 26 hours before functioning.

The No. 880 Mk I is an earlier model of the Fuze No. 880 Mk II, and is identical to the Mk II, except that the arrangement of the shutter holder is sligthly different.

Figure 173 - Tail Fuze No. 880 Mk II