General-purpose machine gun

A general-purpose machine gun (GPMG) is an air-cooled, usually belt-fed machine gun that can be adapted flexibly to various tactical roles for light and medium machine guns. A GPMG will typically feature a quick-change barrel design calibered for various fully powered cartridges such as the 7.62×51mm NATO, 7.62×54mmR, 7.5×54mm French, 7.5×55mm Swiss and 7.92×57mm Mauser, and be configured for mounting to different stabilizing platforms from bipods and tripods to vehicles, aircraft, boats and fortifications, usually as an infantry support weapon or squad automatic weapon.
History.
The general-purpose machine gun (GPMG) originated with the MG 34, designed in 1934 by Heinrich Vollmer of Mauser on the commission of Nazi Germany to circumvent the restrictions on machine guns imposed by the Treaty of Versailles. It was introduced into the Wehrmacht as an entirely new concept in automatic firepower, dubbed the "Einheitsmaschinengewehr", meaning "universal machine gun" in German. In itself the MG 34 was an excellent weapon for its time: an air-cooled, recoil-operated machine gun that could run through belts of 7.92×57mm Mauser ammunition at a rate of 850 rounds per minute, delivering killing firepower at ranges of more than 1,000 meters. The main feature of the MG 34 is that simply by changing its mount, sights and feed mechanism, the operator could radically transform its function: on its standard bipod it was a light machine gun ideal for infantry assaults; on a tripod it could serve as a sustained-fire medium machine gun; mounting on aircraft or vehicles turned it into an air defence weapon, and it also served as the coaxial machine gun on numerous German tanks.
During World War II, the MG 34 was superseded by a new GPMG, the MG 42, although it remained in combat use. The MG 42 was more efficient to manufacture, and more robust, and had an extremely high cyclic rate of fire of 1,200 to 1,500 rounds per minute. One of the GPMG roles was to provide low level anti-aircraft coverage. A high cyclic rate of fire is advantageous for use against targets typically exposed to fire for a limited time span, like aircraft or targets minimizing their exposure by quickly moving from cover to cover. Arguably the finest all-round GPMG ever produced, it was nicknamed "Hitler's buzzsaw" by Allied troops, and alongside the MG 34 it inflicted heavy casualties on Allied soldiers on all European and North African fronts of World War II. Following the war the victorious Allied nations took an interest in the MG 34 and MG 42, influencing many post-war general-purpose machine guns, many still in use today. They lent design elements to the Belgian FN MAG and the American M60, while spawning the Zastava M53, Swiss M51, and Austrian MG 74. Such were the MG 42's qualities of firepower and usability that it became the foundation of an entire series of postwar machine guns, including the MG 1 and MG 3 - the latter, , is still in production.