M4

The M4 is an assault carbine favored by the U.S. SOCOM. It's a descendant of the M1 carbine used in World War II. The "4" refers to the fact that it's the fourth carbine to be officially adopted by the American military. Basically, it was developed for the Special Forces using the M16A as a base. The M4 carries thirty rounds of 5.56mm x 45 SS109s.

The M4 Carbine was originally developed by the U.S. Marines as a carbine version of the venerable M16, providing a rifle's firepower in a lighter and smaller package. This basically gives the firepower of a full Assault Rifle in a more manageable package, hence the name Carbine (A shortened rifle sacrificing some long-range reach and accuracy for maneuverability). There have been Carbine versions of the M16 before (one example is the XM177E1 in MGS: PO), but the M4 thus far is successful enough that the entire U.S. Military has begun replacing most of its M16A2s with M4 Carbines.

The M4A1 is a modular variant of the M4 designed specifically for use with the U.S. Army Special Operations Forces (SOF aka Green Berets), and Navy SEALs. It has a modular mounting system called the FIRM (Floating Integrated Rail Mount, or Picatinny rail system). The system allows the M4A1 to mount any combination of a scope (Normal or Night Vision), vertical front foregrip, the M203 Grenade Launcher, Laser aiming sights (this was the only one used), a breaching shotgun, or a number of accessories. Also, the M4A1 has a detachable carrying handle. This 'flat top' intended for mounting various scopes has also been implemented on select M16A2s already in service. The fully-customized Spec Ops M4A1 is sometimes called the SOCOM rifle due to its use with USSOCOM.

While this gun can be mistaken for the M4A1 used in MGS4, the easiest way to differentiate a regular M4 from an M4A1 is that the standard M4 is set like the M16A2, set for safe, single-shot, and a 3-round burst. The M4A1 on the other hand, has fire settings at safe, single-shot, and full automatic fire.

Although it is not available in the game, the M4A1 also mounts a suppresser. Using the suppresser with standard-issue 5.56mm rounds will lower the firing noise somewhat, but for it to work ideally, the M4A1 must be equipped with subsonic 5.56mm rounds (normal 5.56mm rounds are supersonic). Subsonic rounds, on the other hand, have less range than normal rounds due to their slower velocity.

One other reason for the M4A1's modular design is because of the US Army "Land Warrior" system. Eventually, the M4A1 will mount a mini-camera/infrared scope and links to a targeting computer (worn by the soldier). This rifle's view camera will not only allow a soldier to accurately fire the M4A1 around corners and over obstacles without exposing his head, but also to feed this video to other members of his squad as well. The Land Warrior system is but one of the many applications of Force XXI currently in development.

The U.S-made 5.56mm round was developed as an alternative to the older 7.62mm NATO rounds. Before the 5.56mm (previously known as the .223 Cal Remington), NATO rifles and machineguns were chambered for the bigger 7.62mm round. The 5.56mm was later developed as a scaled-down rifle round, and with the introduction of the M16A1 it quickly became a more popular ammo type, being adopted by NATO soon afterward (as part of STANAG or STandardized NATO AGreement).

The SEALS use the M4A1, and Raiden later picks this weapon up. The weapon is highly accurate and posesses a high rate of fire.