Eugene Stoner designed the Armalite AR-10 rifle to replace the M14 with a lighter and more accurate design that was more reliable in wet and muddy conditions. After the US Military saw the rifle they did some research and came to the conclusion that the next US service rifle needed to have a very fast moving and accurate projectile.
Mr. Stoner scaled down the AR-10 and chambered the rifle in 5.56 x 45mm or .223 Remington as a result of the military’s request.
The AR-15 was born and morphed from the original designation of AR-15(AR stands for Armalite Rifle) to the M16, and then to the M16A1, where it served in the Vietnam War.
The M16A1 became the M16A2, and then was followed by the M4 carbine. Overall the AR-15 platform has been serving American citizens since 1961 and will continue to do so for many decades.