The USP was originally built around the .40 S&W cartridge, but a 9×19mm Parabellum was introduced at the same time. In May 1995, Heckler & Koch introduced a .45 ACP variant. The USP Compact series was introduced in 1996 and is available in 9 mm Parabellum, .40 S&W, .45 ACP, and, exclusively to the Compact model, .357 SIG. Other variants of the standard USP include the USP Tactical, USP Expert, USP Match, USP Elite and the standard sidearm of the German Armed Forces (Bundeswehr)—the P8. The USP Tactical .45 ACP variant is also in limited use by the Bundeswehr, designated as the P12.