There are various ways to deliver an explosive device to a target. These methods use various vehicles including guided missiles, guided or smart artillery shells, dumb artillery shells, guided or smart bombs, and dumb bombs. There are benefits and detriments to each type of device.
Guided missiles are very accurate and include an internal propulsion system. However, the cost per vehicle, missile, is very expensive. Guided or smart artillery shells are not as expensive per item. However, the shell does not have its own propulsion method.
Guided or smart artillery shells have a force-producing device to maneuver the projectile during the flight. The force-producing device can be an aerodynamic device, such as a movable fin, to interact with the airflow which alters the path of the projectile. Projectiles from a rifled cannon and some missiles spin to maintain stability. Other missiles or projectiles may spin simply because they have no device to control or prevent the spin. With the projectile spinning at a high rate, the force-producing device needs to move quickly to account for the spinning of the projectile. A servo-actuator used to reposition the aerodynamic device needs to be capable of moving at a rate sufficient to move the aerodynamic device at a rate that will match to the spin rate of the projectile.
Dumb artillery shells are significantly cheaper per shell than the guided missiles and cheaper than the guided or smart artillery shells. However, when firing dumb artillery shells, the first shells tend to miss their target with a wide dispersion. This delivery process is successful through a trial and correction process to adjust for conditions including environment.