JR Potts, AUS 173d AB (Updated: 11/11/2016):
The conflicts in Panama and Somalia required the need for soldiers to operate in towns and close quarters and mandated the need for a new weapon. This close quarters combat (CQC) was the impetuses behind the M4 with a collapsible stock and a short barrel with accuracy to engage targets at extended ranges with lethal fire. As with many carbines, the M4 is handy and more convenient to carry than a full-length rifle. The Army also will use the weapon for non-infantry troop crews and staff officers who will no longer carry side arms. It is also preferred by airborne units and special operations teams needing effective ranges up to 600 meters.
Variants of the M16 assault rifle, the M4 Carbine and the M4A1 Carbine can be fitted with accessories, night vision devices, laser point optics, telescopic sights, and bipods. The M203 or the M320 grenade launcher are attachable to the M4 top rail. Other accessories include the AN/PEQ-2, Advanced Combat Optical Gunsight (ACOG), and M68 Aimpoint with EOTech holographic weapon sights. Visible and IR (infrared) lights are attachable using various mounting methods. The M4 accepts a blank-firing attachment (BFA) for training.
However all was not well in the military community with the adoption of the M4. The strength of being part of the M16 family was also a negative. In 1969 at Ft. Ord California while I was in a Army basic training live firing class, a drawback for the M16 was demonstrated. The training Sergeant threw a M14 and M16 into a prepared mud puddle and after kicking in more dirt he picked up the M14 and fired the weapon without a stoppage. He then took the M16 and on the initial trigger pull the weapon jammed without firing a shot. This lesson was never to be forgotten that constant cleaning of the M16 was a survival requirement.
During a US Army fair weather and sandstorm condition testing the M4 was compared to 3 competitors and the M4 finished last, with 3.5x more jams than all others tested. Other criticisms of the carbine were a lower muzzle velocity producing a louder report due to the short barrel. Parts receive greater stress and the M4 has a tendency to overheat more rapidly than the M16A2. With agreed upon short comings the US Government purchased the M4 for use in all branches including the National Guard. The Army had the M4 improved and Colt agreed to make modifications going forward to address future problems. A cold-hammer-forged barrel would give a longer life and retooled reliable magazines did reduce the stoppages. 2006 tests which included 10 new M16s and 10 new M4s both fired approximately 5,000 rounds between stoppages, a major improvement.
The M4 Carbine has seen active combat actions in Afghanistan since 2001 and has also been deployed by US forces in Iraq following the invasion of 2003.