The M4 semi-automatic pistol is the sidearm of the ISA in Killzone 1. It is depicted as being a large-caliber, semi-automatic handgun. Judging by the picture from the official strategy guide, the pistol most likely has a polymer frame and a metal slide and barrel. The weapon is chambered for the 50AE cartridge and has a 7 round magazine. It also has decent firepower for a pistol.
- The M4 is loosely based on the real-world Desert Eagle pistol, sharing similar design traits, particularly in the barrel and slide, while the grip is modelled after the Walther P99. The weapon is also chambered for the .50AE cartridge used by the Desert Eagle and has the same magazine capacity of 7 rounds.
- The M4 is slightly unrealistic when being reloaded, e.g. when the player inserts a new clip and releases the slide a new round should already be chambered, but for whatever reason the player re-cocks the pistol and the weapon should eject a round but obviously does not.
- Using the .50AE in combat is highly unrealistic as the round is meant for competition target shooting and sportting use. The gun also lacks the stopping power and kick of a .50AE round.