Any explosive shell requires some mechanism to set it off, preferably on impact. Early shells had been forced to use time fuzes thanks to the difficulty of designing a safe impact fuze for a round shell that might strike in any orientation, but after the introduction of the rifled gun, it was possible to make a fuze that was generally safe until it was fired and set off the shell immediately upon impact. But they generally relied on a pin or wire that sheared on firing to keep the striker from setting off the detonator, and it was entirely possible that if the fuze was struck or dropped, the strike would break loose. Orders were given to disarm and discard any fuze which was struck or dropped, but the possibility of accident was never too far away.

The solution was to look at the various forces imposed on a shell when it was fired. The shock of firing, known as setback, had been used from the start, but it could be duplicated by accidents. Harder to duplicate was the centrifugal force produced by the shell's spin, because it pushed on different parts of the shell differently. The solution was to restrain the striker with two or more spring-loaded safety pins, so that even if a shock was to temporarily dislodge one pin, the other(s) would remain in place. The fuze pictured above has a secondary centrifugal safety feature in the form of a separate firing pin, which is normally concealed within the striker and held in place by the safety pins. When fired, the setback holds it concealed within the striker, and after it leaves the muzzle, the centrifugal force swings it into the unlocked position, a device to make the fuze "boresafe". Also worth noting in this fuze is the creep spring, which is designed to counter the force produced by air resistance on the shell and keep the striker at a distance from the primer until the shell actually hits something.
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