The Heckler & Koch MK 23, MK 23 MOD 0, Mark 23, or USSOCOM MARK 23, is a semi-automatic large-frame pistol chambered in .45 ACP. designed specifically to be an offensive pistol. The USSOCOM version of the MK23 came paired with a laser aiming module (LAM), and suppressor. The USSOCOM MK23 was adopted by the United States Special Operations Command (USSOCOM) for special operations units beating out the nearest competitor, Colt’s OHWS. Development of the pistol began in 1991 as special operations representatives identified the need for an “Offensive Handgun Weapons System—Special Operations Peculiar”, and delivery of the pistols began in May 1996 to the special operation units.

While the USSOCOM MK23 designation usually applies to the complete system, it is also commonly used in reference to the pistol component alone.

The MK 23 is considered a match grade pistol, and is capable of making a 2-inch (51 mm) group at 25 metres (27 yd). The MK 23 is designed for exceptional durability in harsh environments, being waterproof and corrosion-resistant. It uses a polygonal barrel design, which is reported to improve accuracy and durability, and is much more expensive to produce. It also features an ambidextrous safety and magazine release on both sides of the frame. The magazine release is at the rear edge of the trigger guard, which is wide enough to allow the use of gloves. A decocking lever is on the left side, which will silently lower the cocked hammer. The MK 23 is part of a larger weapon system that includes an attachable Laser Aiming Module (LAM), a suppressor,