In the 1980s, the new Squad Automatic Weapon M249 was issued to infantry units, replacing all M60s and some M16A1s at the squad level. In the 1990s the M4 Carbine took over the operational role of the obsolete M3 Grease Gun, some Beretta M9s, and many M16A2s. The US Air Force currently plans to replace all of its M16s with M4s, according to a 2004 presentation. The US Navy decided to retain the M16A2 and M16A3 for its units that use rifles like the US Navy Seabees. The US Army and Marine Corps have largely relegated the M16A2 to non-combat roles, choosing instead the M16A4 and M4. Further, the M16 never entirely replaced the M14 in all roles, which continues to be used in a number of niche applications throughout the Armed Forces, especially with the US Navy.
Replacement of the M16 family has been proposed at various points, and its longevity is in part due to a series of failures in projects meant to replace it, driven largely by the requirement for a significant improvement. Immediately after the introduction of the M16, the Marine Corps sought to adopt the Stoner 63. Although they found it superior in most ways, it was still at an early stage of development; the Marines chose the technically inferior but mature M16. The Advanced Combat Rifle (ACR) program in the 1980s produced weapons that were superior in some ways, but none improved upon the M16 series enough to replace it. It was also potentially going to be replaced by the SABR, from the OICW project. The weapon system originally planned by the OICW project was put on hold around the turn of century, in favor of a simpler new 5.56 mm rifle project that offered less far-reaching improvements. The resulting XM8 rifle was also intended as a potential replacement for the M16 family. However, this program too ran into problems around 2004-5, and was put on hold in favor of a competition for what became known as the OICW Increment 1. This competition was subsequently put on hold in the summer of 2005 to take into account input from other services, and several months later was cancelled outright. Another potential replacement for the M16 rifle is the Special Forces Combat Assault Rifle (SCAR) called the Mark 16 (MK 16). The 5.56x45 MK 16 emerged as the winner of a U.S. SOCOM competition to find a new rifle for Special Forces in 2003. Development by FN Herstal continues and introduction for special forces is expected in late 2007 or early 2008. The Mk.16 offers different length barrels for close quarters combat and for longer-range engagements. Most of the SCAR's basic controls (pistol grip, magazine release, selector lever, and bolt release) share the same location and function as on the M16 and M4 they are supplementing.