Arming

The principal forces used in arming or preparing fuzes for action are (1) set-back, the force of inertia or resistance to linear acceleration of projectiles, and (2) centrifugal force, due to the rotation of the projectile. Many of the Navy fuzes employ a combina-tion of these two forces in arming the fuze. The force of set-back exists only during the acceleration stage of the projectile's flight, which ceases when the projectile leaves the bore of the gun. Centrifugal force, however, exists from the instant that the projectile begins its movement until detonation occurs. Set-back is generally used to shear safety pins, fire psercussion elements, and initiate the operaton of mechanical clocks. Centrifu-gal force serves to release detents of locking pins, drive and fire centrifugally operated clocks, revolve rotor blocks, etc., as is explained in detail in the individual fuze sections following.