The 9×19mm Parabellum (abbreviated 9mm, 9×19mm or 9×19) was designed by Georg Luger in 1902 for Luger semi-automatic pistol. Use of the 9MM began to increase after World War I and 9MM pistols and 9MM submachine guns began being used more widely by military and police. It has become the most popular caliber for U.S. law enforcement because of the wide availability of large magazine capacities that use the 9MM cartridge.
Beginning in early 1980 there was a sharp increase in the use of semiautomatic pistols, especially by the U.S. Army. Prior to this, most law enforcement still issued .38 Special revolvers. Today, there is little doubt that the 9MM is as popular as any round used, either in FMJ or hollow point. The advent of the subsonic 9MM has kept it's popularity increasing in a competitive marketplace. Ballistically superior to the .38 Special and being an autoloading cartridge, it is stored in flat magazines, as opposed to cylindrical loaders or clips. This is one of the main reasons US police departments began trading in their revolvers for some 9mm autoloaders.