The M1 Mortar is an American license-built copy of the French 81mm Brandt mortar. Its true strength, however, lies in the variety of shells available to the typical American mortar operator; delayed detonation, white phosphorus, irritating agents, illuminating shells, etc. Coupled with the availability of these shells, in terms of quantity, means the American infantry battalion enjoyed unmatched firepower advantages. The M1 has become the most widespread 81mm mortar weapon in the world thanks to American industrial overproduction during WW2, and is readily available.