"Rifle, Caliber 5.56 mm, M16". Meanwhile, the Army relented and recommended the adoption of the M16 for jungle warfare operations. However, the Army insisted on the inclusion of a forward assist to help push the bolt into battery in the event that a cartridge failed to seat into the chamber. The Air Force, Colt and Eugene Stoner believed that the addition of a forward assist was an unjustified expense. As a result, the design was split into two variants: the Air Force's M16 without the forward assist, and the "XM16E1 (AKA: M16A1)" with the forward assist for the other service branches. In November 1963, McNamara approved the U.S. Army's order of 85,000 XM16E1s; and to appease LeMay, the Air Force was granted an order for another 19,000 M16s. In March 1964, the M16 rifle went into production and the Army accepted delivery of the first batch of 2129 rifles later that year, and an additional 57,240 rifles the following year. The Colt ArmaLite AR-15 was discontinued with the adoption of the M16 rifle. Most AR-15 rifles in U.S. service have long ago been upgraded to M16 configuration. The Colt ArmaLite AR-15 was also used by the United States Secret Service and other U.S. federal, state and local law enforcement agencies. Shortly after the United States military adopted the M16 rifle, Colt introduced its line semi-automatic-only Colt AR-15 rifles, which it markets to civilians and law enforcement. Colt continues to use the AR-15 name for these rifles. Colt ArmaLite AR-15 (Model 601 and 602) Colt's first two models produced after the acquisition of the rifle from ArmaLite were the 601 and 602, and these rifles were in many ways clones of the original ArmaLite rifle (in fact, these rifles were often found stamped Colt ArmaLite AR-15, Property of the U.S. Government caliber .223, with no reference to them being M16s). The 601 and 602 are virtually identical to the later M16 rifle without the forward-assist. Like the later M16 rifle their charging handle was re-located from under the carrying handle like AR-10 to the rear of the receiver. They were equipped with triangular fore-stocks and occasionally green or brown furniture. Their front sight had a more triangular shape. They had flat lower receivers without raised surfaces around the magazine well. Their bolt hold open device lacked a raised lower engagement surface and had a slanted and serrated surface that had to