Composition B is an explosive consisting of castable mixtures of RDX and TNT as well as, in some instances, additional desensitizing agents. It is used as the main explosive filling in artillery projectiles, rockets, land mines, hand grenades and various other munitions. It was also used for the explosive lenses in the first implosion-type nuclear weapons developed by the United States.
The standard ratio of ingredients (by weight) is 59.5% RDX (detonation velocity of 8,750 m/s) and 39.5% TNT (detonation velocity of 6,900 m/s), together with an additional 1% paraffin wax (Reference: Military Specification MIL-C-401) to improve handling qualities.
Composition B was extremely common in US and other western nations' munitions and was the standard explosive filler from early World War II until the early 1990s, when less sensitive explosives began to replace it in many weapons systems. Some NATO-approved munitions suppliers such as Mecar have continued to use Composition B in their products.
Composition B is occasionally referred to as cyclotol, though the former name is more common.