H&K 45 ACP USC Rifle The USP was originally built around the .40 S&W cartridge, but a 9x19mm 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.
Enhanced versions of the USP, the USP Tactical models are designed for users who need the features found on the HK Mark 23, but in a more compact pistol. USP Tactical pistols approach the precision found on the Mark 23 by adding an extended threaded barrel with a rubber O-ring, adjustable trigger, and adjustable target-type sights. The 9 mm USP SD is a more basic tactical model and is equipped with a threaded barrel and adjustable target sights.