Riding along the internal lands and grooves of the gun tube, these bands create a stabilizing spin as the projectile is fired. Fin-stabilized projectiles may have either fixed fins or folding fins. See Figure 2-23 . Folding fins unfold after the projectile leaves the gun tube to stabilize the projectile. Like projectiles, mortar shells can be filled with explosives, toxic chemicals, WP, or illumination flares.
Mortars generally have thinner metal bodies than projectiles but use the same kind of fuzing.
Like projectiles, mortars are stabilized in flight by fin or spin. Most mortars are fin stabilized, like the ones shown in Figure 2-24 . Other mortars are spin stabilized as shown in Figure 2-25 . A rocket may be defined as a self-propelled projectile. Unlike guided missiles, rockets cannot be controlled in flight.