Gatling filed in 1862 a patent for a weapon more rotating barrels. She initially used paper cartridges that limit its reliability. The tests impressive nonetheless the US Army buys several models in 1865. In 1866, it is modified to fire ammunition with brass case. The operating principle is based on several sets, each consisting of a gun incorporating a bedroom and a percussion mechanism. Upon firing, one of the necessary operations (loading, locking, then percussion extraction and ejection of the case or sleeve) is thus at any time in progress on one of them.