The US Army's Delta Force, at the request of Larry Vickers, co-operated with Heckler & Koch to develop a new carbine in the early 1990's. Originally called the HK M4, the name was changed in response to a trademark infringement suit filed by Colt Defense.
Delta Force adopted the HK416 in 2004 following tests which showed the mechanical reliability of the rifle. Several special operations units as well as the Norwegian Armed Forces also prominently operate the rifle. A modified rifle was also developed and tested as the M27 IAR, of which 452 were made from existing HK416's. Five US infantry battalions operate the IAR.