Editing M2 Browning (section)

==History==
Machine guns were heavily used in World War I, and weapons of larger than rifle caliber began appearing on both sides of the conflict. The larger rounds were needed to pierce the armor that was being introduced to the battlefield, both on the ground and in the air. Germany introduced the [[Junkers J.I]] aircraft, whose armor could render ineffective aircraft machine guns that used conventional rifle ammunition such as the .30-06.<ref name="Chinn 1951 333">{{Harvnb|Chinn|1951|p=333}}, stating "The Germans put a heavily armored plane into service during the closing days of World War I. This act made obsolete for all time the rifle-caliber machine gun for aerial use. Some countries were slower to accept the fact than others but nevertheless, it cannot be disputed. The United States was among the first to come to this realization.<!-- The dramatic incident that caused it was the shooting down by such an aircraft of the young pilot, [[Quentin Roosevelt]]. -->"</ref> Consequently, the [[American Expeditionary Force]]'s commander General [[John J. Pershing]] asked for a larger-caliber machine gun.<ref>{{Harvnb|Chinn|1951|pp=181–182}}</ref> Pershing asked the Army Ordnance Department to develop a machine gun with a caliber of at least {{convert|0.50|in|mm|sigfig=3}} and a muzzle velocity of at least {{convert|2700|ft/s|m/s}}.<ref name="Chinn 1951 333"/>

Around July 1917, John Browning started redesigning his .30-06 [[M1917 Browning machine gun|M1917]] machine gun for a larger and more powerful round. Winchester worked on the cartridge, which was a scaled-up version of the .30-06. Winchester initially added a rim to the cartridge because the company wanted to use the cartridge in an anti-tank rifle, but Pershing insisted the cartridge be rimless.<ref name="Chinn182">{{Harvnb|Chinn|1951|p=182}}</ref> The first .50-caliber machine gun underwent trials on 15 October 1918. It fired at less than 500 rounds per minute, and the muzzle velocity was only {{convert|2300|ft/s|m/s|abbr=on}}. Cartridge improvements were promised.<ref>{{Harvnb|Chinn|1951|p=183}}</ref> The gun was heavy, difficult to control, fired too slowly for the anti-personnel role, and was not powerful enough against armor.<ref>{{Harvnb|Chinn|1951|p=184}}</ref>

While the .50-caliber was being developed, some [[13.2×92mmSR]] [[Mauser 1918 T-Gewehr]] anti-tank rifles and their ammunition were captured. The 13.2 mm German rounds had a muzzle velocity of {{convert|2700|ft/s|m/s|abbr=on}}, an {{convert|800|gr|g|abbr=on}} bullet, and could penetrate armor {{convert|1|inch|mm|abbr=on}} thick at a range of {{convert|250|yard|m|abbr=on}}.<ref>{{Harvnb|Chinn|1951|p=184}}. Chinn states that the German round was 12.7-mm anti-tank, but it may have been the [[13.2mm TuF]] round. The Germans were working on their [[MG 18 TuF]] heavy machine gun.</ref> Winchester improved the .50 caliber round to have similar performance. Ultimately, the muzzle velocity was {{Convert|2750|ft/s|m/s|abbr=on}}.<ref>{{Harvnb|Chinn|1951|p=186}}</ref>

Efforts by Browning and Fred T. Moore resulted in the water-cooled, .50 caliber [[M1921 Browning machine gun]] and an aircraft version. These guns were used experimentally from 1921 until 1937. They had lightweight barrels and the ammunition fed only from the left side. Service trials raised doubts about whether the guns would be suitable for aircraft or for anti-aircraft use. A heavy barrel M1921 was considered for ground vehicles.<ref>{{Harvnb|Chinn|1951|pp=333–335}}</ref>

John M. Browning died in 1926. Between 1927 and 1932, S. H. Green studied the design problems of the M1921 and the needs of the armed services. The result was a single receiver design that could be turned into seven types of .50 caliber machine guns by using different jackets, barrels, and other components. The new receiver allowed right or left side feed. In 1933, Colt manufactured several prototype Browning machine guns (including what would be known as the M1921A1 and M1921E2). With support from the Navy, Colt started manufacturing the M2 in 1933.<ref>{{Harvnb|Chinn|1951|pp=336–337}}</ref> [[FN Herstal]] (Fabrique Nationale) has manufactured the M2 machine gun since the 1930s.<ref>{{cite web |url=http://www.fnherstal.com/index.php?id=655 |title=Major Product Achievements |website=FN Herstal |access-date=2011-09-19 |archive-url=https://web.archive.org/web/20110927060025/http://www.fnherstal.com/index.php?id=655 |archive-date=2011-09-27}}</ref> General Dynamics, U.S. Ordnance and Ohio Ordnance Works Inc. are other current manufacturers.{{Citation needed|date=August 2015}}

A variant without a water jacket, but with a thicker-walled, air-cooled [[gun barrel|barrel]] was designated the M2 HB (''HB'' for ''Heavy Barrel''). The added mass and surface area of the heavy barrel compensated somewhat for the loss of water-cooling, while reducing bulk and weight: the M2 weighs {{convert|121|lb|abbr=on}} with a water jacket, but the M2 HB weighs {{convert|84|lb|abbr=on}}. Due to the long procedure for changing the barrel, an improved system was developed called QCB (quick change barrel). The lightweight "Army/Navy" prefixed '''AN/M2''' "light-barrel" version of the Browning M2 weighing {{Convert|60|lb|kg}} was also developed, and became the standard .50-caliber aviation machine gun of the World War II–era for American military aircraft of nearly every type,<ref>{{cite web |url=http://www.skylighters.org/history/mgs/ |title=AAA Weapons in Focus - The M2 .50-Caliber Machine Gun |website=Skylighters, The Web Site of the 225th AAA Searchlight Battalion |access-date=2008-09-08 |archive-url=https://web.archive.org/web/20080606055546/http://www.skylighters.org/history/mgs/ |archive-date=2008-06-06 |url-status=live}}</ref>{{Better source|date=November 2021}} readily replacing Browning's own [[M1919 Browning machine gun#.30 AN/M2|air-cooled .30 caliber machine gun]] design in nearly all American aircraft installations.{{Cn|date=November 2021}}