In military usage, a shell is a projectile designed primarily for bursting, in distinction from shot, which is designed primarily for penetration of the target. A shell consistt of a steel case, of sufficient strength to withstand the forces of acceleration encountered on firing, containing an explosive charge which may fill the entire cavity of the shell or may be only sufficient to break the case and scatter a charge of gas-, incendiary-, or smoke-producing chemicals. The action of a shell depends largely on the type of fuze with which it is equipped. Shells equipped with time or proximity fuzes detonate in the air a short distance before the target, and scatter their contents, or the fragments of their cases, over a wide area and into shelters, such as trenches and fosholes, which would ordinarily furnish protection from direct fire. Shells equipped with instantaneous-impact fuzes explode on impact , with the ground or a material target, and are effective against personnel or matériel in the open; those equipped with delay fuzes penetrate the target before exploding, and are effective in the demolition of structures and in the destruction of enemy personnel protected by fortifications.
