The HK45 was designed to meet requirements set forth in the U.S. Military Joint Combat Pistol program which had the purpose of arming the U.S. Military with a .45 ACP semi-automatic pistol instead of the 9mm M9 pistol. The Joint Combat Pistol program was suspended indefinitely in 2006, and the M9 pistol remains the standard issue handgun for the U.S. Military. Even though the Joint Combat Pistol program had ended, HK decided to make the HK45 available on the commercial market as well as to law enforcement and military groups. Heckler & Koch, along with Larry Vickers, an ex-Delta Force operator, and Ken Hackathorn led the development of the HK45 to meet Joint Combat Pistol program requirements which was canceled due to the price of re-arming the entire military.
The HK45 represents an evolutionary advancement of the Heckler & Koch USP and shares the same operating principles of that weapon. It is available in the same ten variants as the USP. The HK45 is a full size model pistol, but significant effort went towards making it more ergonomic than the HK USP full-size chambered in .45 ACP by incorporating features found on the Heckler & Koch P2000. These include an extended ambidextrous slide release, a textured ergonomic grip with finger grooves, and interchangeable backstraps to fit differently sized hands. The newer grip and backstraps allow the pistol to sit lower into the web of the hand, contributing to greater control of the weapon and recoil management. In order to accommodate the smaller, more ergonomic grip, the HK45 has a magazine capacity of 10 rounds versus 12 rounds for the USP45. The HK45 also added grip serrations on the front end of the slide, a Picatinny rail in front of the trigger guard for mounting accessories, and an O-ring polygonal barrel similar to the USP Expert and Match models and the Mark 23 for more consistent lock-up of the slide and barrel during cycling and increased accuracy. At least one HK45C Tactical was used in Operation Neptune Spear. The HK45 is also the first weapon to be manufactured at Heckler & Koch's new facility in Newington, New Hampshire.
Heckler & Koch also manufactures the HK45 Compact (HK45C), which can use an 8 round, and a 10 round magazine. The HK45C features the same improvements as the full-size HK45, but has a more conventional straight grip similar to Heckler & Koch's P2000. This design still allows the user to customize the grip size via interchangeable backstraps. An HK45 Tactical (HK45T) and HK45 Compact Tactical (HK45CT) are also available; these variants include an extended threaded barrel for suppressors, and high profile front and rear sights. Extended threaded barrels compatible with the HK45 and HK45C are also available for purchase from Heckler & Koch USA