General-purpose (GP) bombs use a thick-walled metal casing with explosive filler (typically TNT, Composition B, or Tritonal in NATO or United States service) composing about 50% of the bomb's total weight. The British term for a bomb of this type is "medium case" or "medium capacity", abbreviated to MC. The GP bomb is a common weapon of fighter bomber and attack aircraft because it is useful for a variety of tactical applications and relatively cheap. Most modern air-dropped GP bombs are designed to minimize drag for the carrier aircraft.