[6] A variant of the original M1918 BAR, the Colt Monitor machine rifle, remains the lightest production automatic firearm chambered for the .30-06 Springfield cartridge, though the limited capacity of its standard 20-round magazine tended to hamper its utility in that role.

The US entered World War I with an inadequate, small, and obsolete assortment of domestic and foreign machine gun designs, due primarily to bureaucratic indecision and the lack of an established military doctrine for their employment.

The arms donated by the French were often second-rate or surplus and chambered in 8mm Lebel, further complicating logistics as machine gunners and infantrymen were issued different types of ammunition.

[citation needed] By July 1918, the BAR had begun to arrive in France, and the first unit to receive them was the US Army's 79th Infantry Division, which took them into action for the first time on 13 September 1918.

[citation needed] In 1931, the Colt Arms Co. introduced the Monitor Automatic Machine Rifle (R 80), intended primarily for use by prison guards and law-enforcement agencies.

Early prototypes were fitted with barrel-mounted bipods as well as pistol grip housings and a unique rate-of-fire reducer mechanism purchased from FN Herstal.

[citation needed] Production rates greatly increased in 1943, after IBM introduced a method of casting BAR receivers from a new type of malleable iron developed by the Saginaw division of General Motors, called ArmaSteel.

[27] After it successfully passed a series of tests at Springfield Armory, the Chief of Ordnance instructed other BAR receiver manufacturers to change over from steel to ArmaSteel castings for this part.

Changes to the base design include a pistol grip, different type of bipod, open-type V-notch rear sight and a slightly longer barrel.

Additional detail modifications were introduced on the production line; among them were the replacement of the iron sights with a smaller version and reshaping the butt to a fish tail.

[citation needed] In 1920, Belgian arms manufacturer Fabrique Nationale (FN) acquired sales and production rights to the BAR series of firearms in Europe from Colt.

[35] The m/21 would become one of Sweden's main support weapons in the interwar years together with the water-cooled, belt-fed Ksp m/1914 medium machine gun (Swedish adaptation of the Austrian M07/12).

[citation needed] With the cessation of WWI hostilities, Colt Arms Co. received the Browning patents to produce the BAR that had been withheld from issue during the war.

First issued in September 1918 to the American Expeditionary Forces, it was based on the concept of "walking fire", a French practice in use since 1916 for which the CSRG 1915 (Chauchat) had been used accompanying advancing squads of riflemen toward the enemy trenches, as regular machine guns were too cumbersome to move with the troops during an assault.

Given the part-time nature, smaller manning and lesser security of these national guard armories when compared to regular army installations, some BARs were subject to plunder by domestic civilian criminal elements.

[52] The BAR also saw action with US Marine Corps units participating in the Haitian and Nicaraguan interventions, as well as with US Navy shipboard personnel in the course of patrol and gunboat duty along the Yangtze River in China.

[citation needed] When the threat of a new war arose, Ordnance belatedly realized that it had no portable, squad light machine gun, and attempted to convert the M1918 BAR to that role with the adoption of the M1918A2 by the US Army on 30 June 1938.

[55] This doctrine received a setback early in the war after US ground forces encountered German troops, well-armed with automatic weapons including fast-firing, portable machine guns.

In the Pacific, the BAR was often employed at the point or tail of a patrol or infantry column, where its firepower could help break contact on a jungle trail in the event of an ambush.

[60] Despite the improvements in the M1918A2, the BAR remained a difficult weapon to master with its open bolt and strong recoil spring, requiring additional range practice and training to hit targets accurately without flinching.

The weapon's rate-reducer mechanism, a delicately balanced spring-and-weight system described by one ordnance sergeant as a "Rube Goldberg device", came in for much criticism, often causing malfunctions when not regularly cleaned.

[62] The bipod and buttstock rest (monopod), which contributed so much to the M1918A2's accuracy when firing prone on the rifle range, proved far less valuable under actual field combat conditions.

[59] The stock rest was dropped from production in 1942, while the M1918A2's bipod and flash hider were often discarded by individual soldiers and marines to save weight and improve portability, particularly in the Pacific Theater of war.

[62] While not without design flaws (a thin-diameter, fixed barrel that quickly overheated, limited magazine capacity, complex field-strip/cleaning procedure, unreliable recoil buffer mechanism, a gas cylinder assembly made of corrosion-prone metals, and many small internal parts), the BAR proved rugged and reliable enough when regularly field-stripped and cleaned.

In 1944, Captain Wally A. Gayda, of the USAAF Air Transport Command, reportedly used a BAR to return fire against a Japanese Army Nakajima fighter that had attacked his C-46 cargo plane over the Hump in Burma.

[67] General Marshall's report noted that an overwhelming majority of respondents praised the BAR and the utility of automatic fire delivered by a lightweight, portable small arm in both day and night engagements.

[70] As in World War II, many BAR gunners disposed of the heavy bipod and other accoutrements of the M1918A2, but unlike the prior conflict the flash hider was always retained because of its utility in night fighting.

Communist tactical doctrine centered on the mortar and machine gun, with attacks designed to envelop and cut off United Nations forces from supply and reinforcement.

Communist machine gun teams were the best-trained men in any given North Korean or Chinese infantry unit, skilled at placing their heavily camouflaged and protected weapons as close to UN forces as possible.

[citation needed] A retrospective analysis by two American historians stated that Browning Automatic Rifle related shipments had provided "serviceable weapons" yet that the generally "short and slightly built" Vietnamese men using them experienced problems given the nature of "Western standards" around physicality.