The M4 carbine is a family of firearms tracing its lineage back to earlier carbine versions of the M16, all based on the original AR-15 designed by Eugene Stoner and made by ArmaLite. It is a shorter and lighter version of the M16A2 assault rifle, with 80% parts commonality. The M4 and its variants fire 5.56x45mm NATO ammunition (or .223 Remington ammunition) and are gas-operated, air-cooled, magazine-fed, selective fire firearms with a multi-position telescoping stock. Original M4 models had a flat-ended telescoping stock, but newer models are now equipped with a redesigned telescoping stock that is slightly larger with curvature at the end. The M4 is similar to much earlier compact M16 versions, such as the 1960s-era XM177 family. Some of those visual designs are obvious in both weapons, however most of the similarities are not very noticeable. The M4 was intended to replace the .45 ACP M3 submachine gun and selected M9 pistols and M16 rifle series with most Army units (this plan was thought to be changed with the development of the XM29 OICW and the XM8 carbine; however, both projects were cancelled.) The United States Marine Corps has ordered its officers (up to the rank of lieutenant colonel) and Staff Non-commissioned officer to carry the M4 carbine instead of the M9 handgun. This is in keeping with the Marine Corps motto, “Every Marine is a rifleman.” United States Navy corpsmen will also be issued M4s instead of the M9. Some features of the M4 and M4A1 compared to a full-length M16-series rifle. ICS M4/16 incorporates ICS exclusive split gearbox technology. ICS makes the gearbox into two pieces. Split gearbox brings many advantages to airsoft players. The split gearbox is modular design which can simulate the real gun disassembly way. The structure of ICS guns with ICS split gearbox is most similar to a real gun. It gives players most fun to play and the easiest way to maintain and repair the gun. The M4/16 with split gearbox can create similar disassembly ways to a real gun. It also provides players a simple, easy, and fast way to disassemble the gun and simplify the way of maintenance or parts replacement.