Cole Walker's Heckler & Koch Mark 23, is a handgun consisting of a match grade semi-automatic pistol, a laser aiming module (LAM), and suppressor. It was adopted by the United States Special Operations Command (USSOCOM) for special operations units in the 1990s. Cole acquired it, sans the LAM during his tour of duty in Iraq, the weapon having been in the possession of the first Iraqi Cole actually killed in combat. Before that the weapon actually belonged to USSOCOM Lieutenant David Plissken.
While the designation applies to the complete system, it's also commonly used in reference to the pistol component itself. The pistol itself, chambered for the .45 ACP cartridge, was developed by Heckler & Koch, and was selected over the Colt OHWS through USSOCOM's Offensive Handgun Weapon System (OHWS) program. The LAM and suppressor were developed by Insight Technology and Knight's Armament Company (KAC), respectively.
Though the weapon is simply that, its importance to Cole means the man is very protective of it.
The MK23 is considered a match grade pistol, and is capable of making a 2-inch (51 mm) group at 50 yards (46 m), roughly 4 MOA. Production began in 1991, and it was the basis for the HK USP, which began production in 1993. The MK23 has exceptional durability in harsh environments, being waterproof and corrosion-resistant. It uses a polygonal barrel design, which is reported to improve accuracy and durability. 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 MK23 is part of a larger weapon system that includes an attachable laser aiming module, a suppressor, and some other features such as a special high-pressure match cartridge (.45 +P ammunition).
The firearm was tested and found to be capable of firing tens of thousands of rounds without a barrel change. It remains reliable in harsh conditions, making it suitable for use by special forces. The .45 ACP round has considerable stopping power, and yet is subsonic making it suitable for use with a suppressor. Additionally, its shared design characteristics with the Colt M1911 pistol have made it easy for people who have experience with a 1911 to field strip and properly clean the MK23.
However, the firearm's large size and weight have resulted in some criticism. As the handgun was designed for offense rather than defense, the size and weight would help retain higher accuracy, but this also decreased its ease of use, comfort, and draw speed in defensive situations which require a more conventional, compact pistol.