Editing M16 rifle (section)

==History==
===Background===
{{See also|ArmaLite AR-10|ArmaLite AR-15}}
<!-- This section is linked from [[Assault rifle]] -->
In 1928, a U.S. Army 'Caliber Board' conducted firing tests at [[Aberdeen Proving Ground]] and recommended transitioning to smaller caliber rounds, mentioning, in particular {{cvt|.27|in|mm|sigfig=3}} caliber. Largely in deference to tradition, this recommendation was ignored and the Army referred to the {{cvt|.30|in|mm|sigfig=3}} caliber as "full-sized" for the next 35 years.{{sfnp|Fallows|1981|pp=56-65}} After World War II, the United States military started looking for a single automatic rifle to replace the [[M1 Garand]], [[M1 carbine|M1/M2 carbines]], [[M1918 Browning automatic rifle]], [[M3 submachine gun|M3 "Grease Gun"]] and [[Thompson submachine gun]].{{sfnmp|1a1=Ehrhart|1y=2009|1pp=12-16|2a1=Rottman|2y=2011|2p=6}} However, early experiments with select-fire versions of the M1 Garand proved disappointing.{{sfnp|Schreier|2001|p=1}} During the [[Korean War]], the select-fire [[M2 carbine]] largely replaced the [[submachine gun]] in US service{{sfnp|Rottman|2011|p=6}} and became the most widely used carbine variant.{{sfnp|Thompson|2011|p=35}} However, combat experience suggested that the [[.30 carbine]] round was underpowered.{{sfnp|Canfield|2010|p=1}} American weapons designers concluded that an intermediate round was necessary, and recommended a small-caliber, high-velocity cartridge.{{sfnp|Hall|1952|p=593}}

However, senior American commanders, having faced fanatical enemies and experienced major logistical problems during World War II and the [[Korean War]],{{sfnp|''Pacific War Historical Society''|2010}}{{sfnmp|1a1=Appleman|1y=1992|1p=20|2a1=Godfrey|2y=2003|2pp=44-49|3a1=Gropman|3y=1997|3p=25|4a1=Hughes|4a2=Johnson|4y=2005|4p=47}} insisted that a single, powerful .30 caliber cartridge be developed, that could not only be used by the new automatic rifle but by the new [[general-purpose machine gun]] (GPMG) in concurrent development.{{sfnmp|1a1=Harrison|1y=1957|1p=15-17|2a1=Rose|2y=2008|2p=4|3a1=Williams|3y=2014|3p=1}} This culminated in the development of the [[7.62×51mm NATO|7.62×51&nbsp;mm NATO]] cartridge.{{sfnp|Harrison|1957|p=15-17}}

The U.S. Army then began testing several rifles to replace the obsolete M1. Springfield Armory's T44E4 and heavier T44E5 were essentially updated versions of the M1 chambered for the new 7.62&nbsp;mm round, while [[FN Herstal|Fabrique Nationale]] submitted their [[FN FAL]] as the [[T48 rifle|T48]]. [[ArmaLite]] entered the competition late, hurriedly submitting several [[ArmaLite AR-10|AR-10]] prototype rifles in the fall of 1956 to the U.S. Army's Springfield Armory for testing.{{sfnp|Pikula|1998|pp=36, 38}} The AR-10 featured an innovative straight-line barrel/stock design, forged aluminum alloy receivers, and with [[Phenol formaldehyde resin#Applications|phenolic composite]] stocks.{{sfnp|Pikula|1998|pp=27-29}} It had rugged elevated sights, an oversized aluminum{{NoteTag|Later changed to titanium.{{sfnp|Pikula|1998|p=38}} }} [[flash suppressor]] and [[muzzle brake|recoil compensator]], and an adjustable gas system.{{sfnp|Pikula|1998|pp=27-30}} The final prototype featured an upper and lower receiver with the now-familiar hinge and takedown pins, and the [[charging handle]] was on top of the receiver placed inside of the carry handle.{{sfnp|Pikula|1998|pp=36, 38}} For a 7.62&nbsp;mm NATO rifle, the AR-10 was incredibly lightweight at only {{cvt|6.85|lb|kg}} empty.{{sfnp|Pikula|1998|pp=36, 38"}} Initial comments by Springfield Armory test staff were favorable, and some testers commented that the AR-10 was the best lightweight automatic rifle ever tested by the Armory.{{sfnmp|1a1=Lewis|1y=1962|1p=21|2a1=Pikula|2y=1998|2pp=39-40}} In the end, the U.S. Army chose the T44, now named the [[M14 rifle]],{{sfnp|Harrison|1957|p=15-17}} which was an improved [[M1 Garand]] with a 20-round magazine and automatic fire capability.{{sfnp|Bruce|2002|pp=20-27}}{{NoteTag|Per ''Jane's International Defense Review:'' "The M14 is basically an improved M1 with a modified gas system and detachable 20-round magazine."{{sfnp|''Jane's International Defense Review'', April 2003, p.43}}}}  The U.S. also adopted the [[M60 machine gun|M60]] general-purpose machine gun (GPMG).{{sfnp|Harrison|1957|p=15-17}} Its NATO partners adopted the FN FAL and [[HK G3]] rifles, as well as the [[FN MAG]] and [[Rheinmetall MG3]] GPMGs.

The first confrontations between the [[AK-47]] and the M14 came in the early part of the [[Vietnam War]]. Battlefield reports indicated that the M14 was uncontrollable in full-auto and that soldiers could not carry enough ammunition to maintain fire superiority over the AK-47.{{sfnmp|1a1=Bruce|1y=2002|1pp=20-27|2a1=Emerson|2y=2006|2p=1}} And, while the M2 carbine offered a high rate of fire, it was under-powered and ultimately outclassed by the AK-47.{{sfnp|Rottman|2011|p=41}} A replacement was needed: a medium between the traditional preference for high-powered rifles such as the M14, and the lightweight firepower of the M2 carbine.{{sfnp|Godfrey|2003|pp=44-49}}

As a result, the Army was forced to reconsider a 1957 request by General [[Willard G. Wyman]], commander of the U.S. Continental Army Command (CONARC) to develop a .223-inch caliber (5.56&nbsp;mm) select-fire rifle weighing {{convert|6|lb|kg|abbr= on}} when loaded with a 20-round magazine.{{sfnp|Ehrhart|2009|p=16-19}} The 5.56&nbsp;mm round had to penetrate a standard U.S. helmet at {{convert|500|yd|m|abbr=off|sp=us}} and retain a velocity over the speed of sound while matching or exceeding the wounding ability of the .30 carbine cartridge.{{sfnp|Hutton|1970|pp=32-41}}

This request ultimately resulted in the development of a scaled-down version of the [[Armalite AR-10]], named the [[ArmaLite AR-15]].{{sfnmp|1a1=Ezell|1a2=Pegg|1a3=Smith|1a4=Smith|1y=1993|1pp=46-47|2a1=Kern|2y=2006|2p=10|3a1=Kokalis|3y=2010|3p=1}} The AR-15 was first revealed by [[Eugene Stoner]] at Fort Benning in May 1957.{{sfnp|Rottman|2011|p=8}} The AR-15 used .22-caliber bullets, which destabilized when they hit a human body, as opposed to the .30 round, which typically passed through in a straight line. The smaller caliber meant that it could be controlled in auto fire due to the reduced [[bolt thrust]] and [[free recoil]] impulse. Being almost one-third the weight of the .30 meant that the soldier could sustain fire for longer with the same load. Due to design innovations, the AR-15 could fire 600 to 700 rounds a minute with an extremely low jamming rate. Parts were stamped out, not hand-machined, so they could be mass-produced, and the stock was plastic to reduce weight.{{sfnp|Fallows|1981|pp=56-65}}

In 1958, the Army's Combat Developments Experimentation Command ran experiments with small squads in combat situations using the M14, AR-15, and Winchester's Light Weight Military Rifle (WLWMR).<ref>{{cite web|url=https://www.americanrifleman.org/content/the-contender-winchester-s-224-light-rifle/|title=The Contender: Winchester's .224 Light Rifle|website=American Rifleman|date=February 19, 2016|access-date=February 19, 2016}}</ref> The resulting study recommended adopting a lightweight rifle like the AR-15. In response, the Army declared that all rifles and machine guns should use the same ammunition and ordered full production of the M14.{{sfnp|Fallows|1981|pp=56-65}} However, advocates for the AR-15 gained the attention of Air Force Chief of Staff General [[Curtis LeMay]]. After testing the AR-15 with the ammunition manufactured by Remington that Armalite and Colt recommended, the Air Force declared that the AR-15 was its 'standard model' and ordered 8,500 rifles and 8.5 million rounds.{{sfnp|Fallows|1981|pp=56-65}} Advocates for the AR-15 in the [[Defense Advanced Research Projects Agency]] acquired 1,000 Air Force AR-15s and shipped them to be tested by the [[Army of the Republic of Vietnam]] (ARVN). The South Vietnam soldiers issued glowing reports of the weapon's reliability, recording zero broken parts while firing 80,000 rounds in one stage of testing, and requiring only two replacement parts for the 1,000 weapons over the entire course of testing. The report of the experiment recommended that the U.S. provide the AR-15 as the standard rifle of the ARVN, but Admiral [[Harry Felt]], then Commander in Chief of Pacific Forces, rejected the recommendations on the advice of the U.S. Army.{{sfnp|Fallows|1981|pp=56-65}}

Throughout 1962 and 1963, the U.S. military extensively tested the AR-15. Positive evaluations emphasized its lightness, "lethality", and reliability.{{sfnp|Fallows|1981|pp=56-65}} However, the [[United States Army Materiel Command|Army Materiel Command]] criticized its inaccuracy at longer ranges and lack of penetrating power at higher ranges.{{sfnmp|1a1=Bruce|1y=2002|1pp=20-27|2a1=Fallows|2y=1981|2pp=56-65|3a1=Kern|3y=2006|3p=10}} In early 1963, the [[U.S. Special Forces]] asked and was given permission, to make the AR-15 its standard weapon. Other users included Army Airborne units in Vietnam and some units affiliated with the [[Central Intelligence Agency]]. As more units adopted the AR-15, Secretary of the Army [[Cyrus Vance]] ordered an investigation into why the weapon had been rejected by the Army. The resulting report found that Army Materiel Command had rigged the previous tests, selecting tests that would favor the M14 and choosing [[match grade]] M14s to compete against AR-15s out of the box.{{sfnp|Fallows|1981|pp=56-65}} At this point, the bureaucratic battle lines were well-defined, with the Army ordnance agencies opposed to the AR-15 and the Air Force and civilian leadership of the Defense Department in favor.{{sfnp|Fallows|1981|pp=56-65}}

In January 1963, Secretary of Defense Robert McNamara concluded that the AR-15 was the superior weapon system and ordered a halt to M14 production.{{sfnmp|1a1=Bruce|1y=2002|1pp=20-27|2a1=Kern|2y=2006|2p=10}} In late 1963, the Defense Department began mass procurement of rifles for the Air Force and special Army units. Secretary McNamara designated the Army as the procurer for the weapon with the Department, which allowed the Army ordnance establishment to modify the weapon as they wished. The first modification was the addition of a "manual bolt closure", allowing a soldier to ram in a round if it failed to seat properly. The Air Force, which was buying the rifle, and the Marine Corps, which had tested it both objected to this addition, with the Air Force noting, "During three years of testing and operation of the AR-15 rifle under all types of conditions the Air Force has no record of malfunctions that could have been corrected by a manual bolt closing device." They also noted that the closure added weight and complexity, reducing the reliability of the weapon. Colonel Harold Yount, who managed the Army procurement, would later state the bolt closure was added after direction from senior leadership, rather than as a result of any complaint or test result, and testified about the reasons: "the M-1, the M-14, and the carbine had always had something for the soldier to push on; that maybe this would be a comforting feeling to him or something."{{sfnmp|1a1=Fallows|1y=1981|1pp=56-65|2a1=Morgan|2y=1967|2p=4545}}

After modifications, the new redesigned rifle was subsequently adopted as the M16 Rifle:{{sfnmp|1a1=Bruce|1y=2002|1pp=20-27|2a1=Defense Technical Information Center (DTIC)|2y=1968|2p=5|3a1=Kern|3y=2006|3p=10|4a1=Kokalis|4y=2010|4p=2}}
{{blockquote|(The M16) was much lighter compared to the M14 it replaced, ultimately allowing soldiers to carry more ammunition. The air-cooled, gas-operated, magazine-fed assault rifle was made of steel, aluminum alloy, and composite plastics, truly cutting-edge for the time. Designed with full and semi-automatic capabilities, the weapon initially did not respond well to wet and dirty conditions, sometimes even jamming in combat. After a few minor modifications, the weapon gained in popularity among troops on the battlefield.{{sfnmp|1a1=Bruce|1y=2002|1pp=20-27|2a1=Haas|2y=2013|2p=67}}{{NoteTag|Per Haas: "Nicknamed a 'Mattel toy'{{sfnp|Coomer|1968|p=25}} because of its small caliber and lightweight design, the M16 became the standard service rifle for U.S. forces in Vietnam in 1967. The weapon was much lighter compared to the M14 it replaced, ultimately allowing Soldiers to carry more ammunition. The air-cooled, gas-operated, magazine-fed assault rifle was made of steel, aluminum alloy and composite plastics, truly cutting-edge for the time. Designed with full and semi-automatic capabilities, the weapon initially did not respond well to wet and dirty conditions, sometimes even jamming in combat. After a few minor modifications, the weapon gained in popularity among troops on the battlefield. Still in service today, the M16 is being phased out by the M4 carbine.}} }}

Despite its early failures the M16 proved to be a revolutionary design and stands as the longest continuously serving rifle in US military history.{{sfnmp|1a1=Defense Technical Information Center (DTIC)|1y=1968|1p=5|2a1=Kern|2y=2006|2p=10}} It has been adopted by many US allies and the [[5.56×45mm NATO|5.56×45&nbsp;mm NATO]] cartridge has become not only the NATO standard but "the standard assault-rifle cartridge in much of the world."{{sfnmp|1a1=Arvidsson|1y=2009|1p=8|2a1=Dougherty|2y=2012|2p=26|3a1=Kern|3y=2006|3p=10}} It also led to the development of small-caliber high-velocity service rifles by every major army in the world.{{sfnp|Kern|2006|p=10}} It is a benchmark against which other assault rifles are judged.{{sfnp|Kern|2006|p=10}}{{NoteTag|Per Gourley: "Colt literature notes that the fourth generation of the M16 "still represents the world standard by which all other weapons of this class are judged. Its combat-proven performance is verified by the fact that over eight million M16 weapon systems have been produced and placed in military service throughout the world."{{sfnp|Gourley|2008|p=75}}<br /> Per Valpolini: "Among western armies the M4 with its 356-mm-long barrel remains the benchmark type, although reports from the field have shown some criticism regarding its reliability in sand and dusty environments due to the direct impingement or 'gas-tube' system that tends to bring carbon blow-back into the chamber, while hot gases used to cycle the weapon generate heat problems."{{sfnp|Valpolini|2012|p=3}} }}

===Adoption===
[[File:M16a1m16a2m4m16a45wi.jpg|thumb|From top to bottom: [[#XM16E1 and M16A1 (Colt Model 603)|M16A1]], [[#M16A2|M16A2]], [[M4 carbine#M4A1|M4A1]], [[#M16A4|M16A4]].]]
[[File:Ricards King Cleans His M-16, 19 December 1967 (29259454721).jpg|thumb|right|A Marine of the [[3rd Battalion, 1st Marines]] cleans his XM16E1 in December 1967.]]

In July 1960, General Curtis LeMay was impressed by a demonstration of the ArmaLite AR-15. In the summer of 1961, General LeMay was promoted to U.S. Air Force chief of staff and requested 80,000 AR-15s. However, General [[Maxwell D. Taylor]], [[chairman of the Joint Chiefs of Staff]], advised President [[John F. Kennedy]] that having two different calibers within the military system at the same time would be problematic and the request was rejected.{{sfnp|Rose|2008|p=372}} In October 1961, William Godel, a senior man at the [[DARPA|Advanced Research Projects Agency]], sent 10 AR-15s to South Vietnam. The reception was enthusiastic, and in 1962 another 1,000 AR-15s were sent.{{sfnp|Rose|2008|pp=372–373}} [[United States Army Special Forces]] personnel filed battlefield reports lavishly praising the AR-15 and the stopping power of the 5.56&nbsp;mm cartridge and pressed for its adoption.{{sfnp|Bruce|2002|pp=20-27}}

The damage caused by the 5.56&nbsp;mm bullet was originally believed to be caused by "tumbling" due to the slow 1 turn in {{convert|14|in|mm|adj=on}} rifling twist rate.{{sfnmp|1a1=Bruce|1y=2002|1pp=20-27|2a1=Rose|2y=2008|2p=372}} However, any pointed lead core bullet will "tumble" after penetration into flesh, because the center of gravity is towards the rear of the bullet. The large wounds observed by soldiers in Vietnam were caused by bullet fragmentation created by a combination of the bullet's velocity and construction.{{sfnp|''AR15.com''|2008}} These wounds were so devastating that the photographs remained classified into the 1980s.{{sfnp|Rose|2008|p=373}}

However, despite overwhelming evidence that the AR-15 could bring more firepower to bear than the M14, the Army opposed the adoption of the new rifle.{{sfnmp|1a1=Bruce|1y=2002|1pp=20-27|2a1=Kern|2y=2006|2p=10}} U.S. [[United States Secretary of Defense|Secretary of Defense]] [[Robert McNamara]] now had two conflicting views: the ARPA report{{sfnp|''DARPA''| 1962}} favoring the AR-15 and the Army's position favoring the M14.{{sfnp|Bruce|2002|pp=20-27}} Even President Kennedy expressed concern, so McNamara ordered Secretary of the Army, Cyrus Vance, to test the M14, the AR-15, and the AK-47. The Army reported that only the M14 was suitable for service, but Vance wondered about the impartiality of those conducting the tests. He ordered the Army Inspector General to investigate the testing methods used; the inspector general confirmed that the testers were biased toward the M14.

In January 1963, Secretary McNamara received reports that M14 production was insufficient to meet the needs of the armed forces and ordered a halt to M14 production.{{sfnp|Bruce|2002|pp=20-27}} At the time, the AR-15 was the only rifle that could fulfill a requirement of a "universal" infantry weapon for issue to all services. McNamara ordered its adoption, despite receiving reports of several deficiencies, most notably the lack of a [[Chrome plating|chrome-plated]] chamber.{{sfnmp|1a1=Defense Technical Information Center (DTIC)|1y=1968|1p=5|2a1=Sweeney|2a2=Ferguson|2y=2004|2p=240}}

After modifications (most notably, the charging handle was re-located from under the carrying handle like the AR-10, to the rear of the receiver),{{sfnp|Kokalis|2010|p=2}} the newly redesigned rifle was renamed the ''Rifle, Caliber 5.56&nbsp;mm, M16''.{{sfnp|Defense Technical Information Center (DTIC)|1968|p=5}}{{sfnp|Kern|2006|p=10}} Inexplicably, the modification to the new M16 did not include a chrome-plated barrel. 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 if 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 with the forward assist for the other service branches.

In November 1963, McNamara approved the U.S. Army's order of 85,000 XM16E1s;{{sfnmp|1a1=Bruce|1y=2002|1pp=20-27|2a1=Rose|2y=2008|2pp=380, 392}} and to appease General LeMay, the Air Force was granted an order for another 19,000 M16s.{{sfnmp|1a1=Ezell|1a2=Pegg|1a3=Smith|1a4=Smith|1y=1993|1pp=46-47|2a1=Rose|2y=2008|2p=380}} In March 1964, the M16 rifle went into production and the Army accepted delivery of the first batch of 2,129 rifles later that year, and an additional 57,240 rifles the following year.{{sfnp|Defense Technical Information Center (DTIC)|1968|p=5}}

In 1964, the Army was informed that [[DuPont]] could not mass-produce the [[Improved military rifle powder#IMR|IMR 4475]] stick powder to the specifications demanded by the M16. Therefore, [[Olin Corporation|Olin Mathieson Company]] provided a high-performance [[ball propellant]]. While the Olin WC 846 powder achieved the desired {{convert|3300|ft|m|abbr=on}} per second muzzle velocity, it produced much more fouling, which quickly jammed the M16's action (unless the rifle was cleaned well and often).{{sfnp|Fallows|1981|pp=56-65}}

In March 1965, the Army began to issue the XM16E1 to infantry units. However, the rifle was initially delivered without adequate cleaning kits{{sfnp|Bruce|2002|pp=20-27}} or instructions because advertising from Colt asserted that the M16's materials made the weapon require little maintenance, leading to a misconception that it was capable of self-cleaning.{{sfnp|Rottman|2011|p=20}} Furthermore, cleaning was often conducted with improper equipment, such as [[insect repellent]], water, and aircraft fuel, which induced further wear on the weapon.{{sfnp|Rottman|2011|p=24}} As a result, reports of stoppages in combat began to surface.{{sfnp|Bruce|2002|pp=20-27}} The most severe problem was known as "failure to extract"—the spent cartridge case remained lodged in the chamber after the rifle was fired.{{sfnp|Bruce|2002|pp=20-27}}{{sfnp|''The New York Times, At War Blog'', November 12, 2009}} Documented accounts of dead U.S. troops found next to disassembled rifles eventually led to a Congressional investigation:{{sfnmp|1a1=Bruce|1y=2002|1pp=20-27|2a1=Fuerbringer|2y=1967|2p=7}}

{{Blockquote|We left with 72 men in our platoon and came back with 19. ...Believe it or not, you know what killed most of us? Our own rifle. Practically every one of our dead was found with his (M16) torn down next to him where he had been trying to fix it.|Marine Corps Rifleman, Vietnam.{{sfnp|Fuerbringer|1967|p=7}} }}

In February 1967, the improved XM16E1 was standardized as the M16A1.{{sfnp|Ezell|Pegg|Smith|Smith|1993|pp=46-47}} The new rifle had a chrome-plated chamber and bore to eliminate corrosion and stuck cartridges, and other minor modifications.{{sfnp|Bruce|2002|pp=20-27}} New cleaning kits, powder solvents, and lubricants were also issued. Intensive training programs in weapons cleaning were instituted including a comic book-style operations manual.{{sfnmp|1a1=Eisner|1y=1968|1p=4|2a1=Rottman|2y=2011|2p=79}} As a result, reliability problems were largely resolved and the M16A1 rifle achieved widespread acceptance by U.S. troops in Vietnam.{{sfnmp|1a1=Bruce|1y=2002|1pp=20-27|2a1=Coomer|2y=1968|2p=7}}

In 1969, the M16A1 officially replaced the M14 rifle to become the U.S. military's standard [[service rifle]].{{sfnp|Ezell|Pegg|Smith|Smith|1993|pp=746–762}}{{sfnp|Urdang|1968|p=801}} In 1970, the new WC 844 powder was introduced to reduce fouling.{{sfnp|Watters|2004|p=1}}

Colt, H&R, and GM Hydramatic Division manufactured M16A1 rifles during the Vietnam War.<ref>{{cite web |last= Iannamico|first= Frank|date= 15 December 2022|title=Forgotten M16A1 Rifle Manufacturers: GM/Hydra-Matic and Harrington & Richardson – Part I|url= https://smallarmsreview.com/forgotten-m16a1-rifle-manufacturers-part-i-gm-hydra-matic-and-harrington-richardson/|website=smallarmsreview.com |access-date= 15 April 2025}}</ref> M16s were produced by Colt until the late 1980s when FN Herstal (FN USA) began to manufacture them.{{sfnp|Rosenthal|1988|p=32}}