The M16 (officially Rifle, Caliber 5.56mm, M16) is the United States Armed Forces designation for a variation of the AR-15 rifle. The Colt Company purchased the rights to the AR-15 from ArmaLite and currently only uses that designation for semi-automatic versions of the rifle. The M16 fires the 5.56 × 45 NATO cartridge. It entered service with the United States Army and was first deployed for Vietnam War operations in South Vietnam in 1963.5 becoming the standard rifle for the FF. AA. in 1969.6 replacing the M14 rifle in that role. The United States military kept the M14 in service in the continental United States, Europe, and South Korea until 1970. The M16 has been widely adopted by armies around the world.7 8 9 10 Total production The number of M16 rifles since the beginning of its design is approximately eight million, 4 being the most produced weapon of its caliber.11 The M16 was replaced in the United States Army by the M4 carbine, which is a short version derived from the M16A2.12

Traditionally, the US military was in favor of long-range precision shooting; the soldier was taught to shoot from afar and take the first shot. Therefore, they were looking for powerful ammunition and rifles that fired with great precision, such as the M1 Garand13.

After the Korean War, the US Army saw the futility of powerful cartridges and decided to seriously search for an assault rifle that could replace the M1 Garand. At the same time, following the path indicated by Germany with its Stg 44 rifles, a less powerful but effective cartridge that could be used in combat was being investigated and the final result was the NATO 5.56 × 45 cartridge. In fact, other NATO countries were also developing and testing weapons that fired small-caliber cartridges.

Many officers called for this new weapon to be lightweight, reliable, accurate, and capable of firing in automatic mode. The FN FAL, two heavier and improved versions of the Garand and the AR-10, were presented to the competition called to find the new assault rifle. The AR-10 was promising but too eco-friendly for the time, so its designer, Eugene Stoner, was encouraged to mature the design.

The weapon finally chosen was the M14 rifle. When shooting in auto mode, it is very imprecise and uncontrollable. A lighter cartridge if it allowed a more accurate automatic firing. In addition, many people in the Army did not think it was the weapon that was needed, especially for combat in scenarios where people did not shoot at great distances. A weapon was also wanted that would allow the soldier to carry more ammunition and prevent it from running out in combat. Furthermore, in the 1950s, the helicopter began to require light infantry forces and aircraft.15

The AR-15 rifle
Main article: AR-15
The M16 assault rifle is an improved version of the AR-15 rifle and was a lower caliber version of the AR-10 combat rifle, designed by Eugene Stoner. At first it encountered several obstacles from the generals and personnel of the Defense Advanced Projects Research Agency or DARPA (acronym in English), since they had a preference for larger calibers, in addition to being the first assault rifle built. with composite materials (steel, aluminum and plastic). The concept held promise for an army that saw the future of air mobility by equipping soldiers with an assault rifle and lighter ammunition.14 General Willard G. Wyman was familiar with munitions research and the benefits it provided. he offered the 5.56mm cartridge and asked Stoner to design the AR-15 to take advantage of those benefits.15

The AR-15 waited two years for it to be finally accepted into the Armed Forces; In a demonstration, General Curtis LeMay ordered 8500 AR-15s to replace the old M1 and M2 carbines in the defense of Strategic Air Command air bases; however, Defense Secretary Robert McNamara revoked the request.

This did not stop US special operations units and advisers in Vietnam from obtaining AR-15 rifles. In 1962, 1,000 XM177 E1 / E2 rifles (actually AR-15) were shipped to be battle tested by American advisers and South Vietnamese Rangers. The American advisers confirmed the benefits of the AR-15 in combat and sent very favorable reports. The Pentagon wanted to arm the South Vietnamese army with a modern weapon, and the AR-15 offered advantages over the M14, being better suited for weight and size. After multiple discussions in early 1963, a larger order was placed.