The MG34 was the first German implementation of the universal machine gun concept - and really the first such fielded by any army. The idea was to have a single weapon which could be used as a light machine gun, heavy machine gun, vehicle gun, fortification gun, and antiaircraft gun. The MG34 was designed to be light enough for use as an LMG, to have a high enough rate of fire to serve as an antiaircraft gun, to be compact and flexible enough for use in vehicles and fortifications, and to be mounted on a complex and advanced tripod for use as a heavy machine gun.
Mechanically, the MG34 is a recoil operated gun using a rotating bolt for locking. It is chambered for 8mm Mauser, and feeds from 50-round belt segments with a clever and unique quick-change barrel mechanism. The early versions were fitted with adjustable rate reducers in the grips allowing firing from 400 to 900 rounds per minute, and also had an option for a top cover which would fit a 75-round double drum magazine. Both of these features were rather quickly discarded, however,r in the interest of more efficient production. However, the gun fulfilled its universal role remarkably well.
The MG34 was considered a state secret when first developed, and despite entering production in 1936 it would not be formally adopted until 1939 - by which time 50,000 or so had already been manufactured. It would comprise about 47% of the machine guns in German service when the Wehrmacht invaded Poland, but would be fully standardized by March of 1941. It was replaced by the MG42 later in the war, as that weapon was both faster and cheaper to produce and also required substantially less of the high-grade steel alloys that Germany had limited supplies of. However, it would continue to be produced through the war, particularly for vehicle mounts.
Cool Forgotten Weapons merch! http://shop.bbtv.com/collections/forgotten-weapons