In 1993, Heckler & Koch introduced the Universelle Selbstladepistole, or "Universal Self-loading Pistol", a large polymer-frame autoloader pistol, chambered in the emerging .40S&W caliber and designed for the US law enforcement market. Unlike other .40S&W handguns available at the time, the USP was specifically designed for .40S&W, rather than being based on a pre-existing 9x19mm design.
The USP arose as a somewhat scaled-down sibling to the HK MK23 USSOCOM pistol, introduced in 1991. The MK23 is an extremely large polymer-frame autoloader chambered in .45ACP and designed for special military use. Although similar in construction to a USP, the MK23 features a heavier frame, threaded barrel, match trigger and adjustable sights. Most importantly though, the MK23 is chambered exclusively in .45ACP, while the original USP is only available in .40S&W and 9x19mm calibers.
The MK23 also has a significant drawback: its incredible size. Although its large size affords it extreme accuracy, stability and indestructibility, the MK23 is not a particularly practical firearm for most applications. In an effort to address the drawbacks of both the MK23 and USP, HK developed the USP45. Introduced in 1995, the USP .45 employs a slightly enlarged USP frame, and is chambered in .45ACP.
HK USP .45, full size frame, Version 1 trigger group, 12-round high capacity magazine.
USP .45, slide retracted.
Three years later, HK introduced the USP .45 Tactical, completing the hybridization of the MK23 and USP platforms. The Tactical adds to the standard USP45 a threaded MK23-style barrel, match trigger and adjustable sights. The USP .45 Tactical is generally considered to be one of the most balanced and effective defensive handguns ever built, with virtually all of the advantages of a MK23 packed into a handgun of rational size.
HK USP .45 Tactical, full size frame, Version 1 trigger group, 12-round high capacity magazine.
USP .45 Tactical, safety/decock lever.
The USP .45 Tactical has a threaded barrel with Viton O-ring. The O-ring is intended to improve accuracy, but most users cannot discern any improvement.
The USP family was designed for the US firearms market, employing a modified Browning action and familiar Colt 1911-style controls and handling. Although mechanically similar, the USP is not suceptible to many problems associated with the 1911, including most types of cycling failures and internal breakages. The USP also offers nearly double the capacity of the single-stack 1911.
One of the most notable features of the MK23 and USP is the incorporation of an under-barrel mounting rail, capable of accepting various accessories like flashlights and lasers. This feature has since become standard on virtually all tactical handguns from all major manufacturers, although the industry ultimately adopted the military standard picatinny rail dimensions, while the MK23 and USP use a proprietary HK rail design which is only compatible with accessories specifically designed for it. HK would not implement a standard Picatinny accessory rail until the introduction of the HK45 in 2007. The HK45 is a somewhat streamlined USP-style handgun with a lighter frame, adjustable backstrap, match trigger and adjustable sights. Its primary drawback is a reduced ammunition capacity compared to the USP .45.
