introduced in World War I. Base and nose ejection are almost always used with airburst fuzes. Bursting shells use various types of fuze depending on the nature of the payload and the tactical need at the time. Payloads have included: Bursting: high-explosive, white phosphorus, coloured marker, chemical, nuclear devices; high-explosive anti-tank and canister may be considered special types of bursting shell. Nose ejection: shrapnel, star, incendiary and flechette (a more modern version of shrapnel). Base ejection: Dual-Purpose Improved Conventional Munition bomblets, which arm themselves and function after a set number of rotations after having been ejected from the projectile (this produces unexploded sub-munitions, or "duds", which remain dangerous), scatterable mines, illuminating, coloured flare, smoke, incendiary, propaganda, chaff (foil to jam radars) and modern exotics such as electronic payloads and sensor-fuzed munitions. Stabilization Rifled: Artillery projectiles have traditionally been spin-stabilised, meaning that they spin in flight so that gyroscopic forces prevent them from tumbling. Spin is induced by gun barrels having rifling, which engages a soft metal band around the projectile, called a "driving band" (UK) or "rotating band" (U.S.). The driving band is usually made of copper, but synthetic materials have been used. Smoothbore/fin-stabilized: In modern artillery, smoothbore barrels have been used mostly by mortars. These projectiles use fins in the airflow at their rear to maintain correct orientation. The primary benefits over rifled barrels is reduced barrel wear, longer ranges that can be achieved (due to the reduced loss of energy to friction and gas escaping around the projectile via the rifling) and larger explosive cores for a given caliber artillery due to less metal needing to be used to form the case of the projectile because of less force applied to the shell from the non-rifled sides of the barrel of smooth bore guns. Rifled/fin-stabilized: A combination of the above can be used, where the barrel is rifled, but the projectile also has deployable fins for stabilization, guidance or gliding. Propellant Most forms of artillery require a propellant to propel the projectile at the target. Propellant is always a low explosive, which means it deflagrates, rather than detonating like high explosives. The shell is accelerated to a high velocity in a very short time by the rapid generation of gas from the burning propellant. This high pressure is achieved by burning the propellant in a contained area, either the chamber of a gun barrel or the combustion chamber