The belligerents of World War 2 (1939-1945) all used several classes of machine guns for their respective ground forces, mainly centering on light-, medium- and heavy-class types to cover various battlefield roles. For the Italian Army, the Breda Model 1930 served as its standard light machine gun and this was followed by the FIAT-Revelli Model 1914 to fill the medium role. For its heavy-class needs, the Army selected the Breda Model 1937 just prior to the start of the war with its original intention that it be installed in Italian tanks as coaxial weapons - thus inheriting qualities that limited it as an infantry field weapon.
Back in 1930, the Breda concern acquired production rights to the useful French Hotchkiss machine gun in 13.2mm form and repackaged/resold it as the "Breda Model 1931". After also acquiring the gun-making interests of FIAT, Breda further broadened its approach in the machine gun market resulting in the "Breda Model 1935". This product was evolved into light, medium and heavy machine gun forms as well as vehicle-mounted types. The Model 1937 - in design as early as 1933 - followed and, from the outset, relied on a larger, more powerful rifle caliber cartridge in the 8x59mm RB Breda. Trials of the new gun spanned from 1935 to 1936 with service entry granted in 1937.
Internally, the Model 1937 relied on a conventional gas-driven piston operation with tilting bolt action and, on the whole, the weapon was largely traditional in its design save a few unique elements. A large, rectangular receiver housed the internal working components and spade grips were set at the rear near the trigger unit. The barrel, air-cooled by design, was long and slender with the gas cylinder fitted underneath. Iron sights were fitted for ranged work. For when in the defense/infantry support role the weapon was typically sat atop a heavy-duty tripod but could just as easily be arranged for service in/on vehicles as needed.
The limitations of the Model 1937 were some of the same seen in earlier Breda machine gun designs - cartridge extraction issues were apparent and dealt with through a cumbersome lubrication system which tempted all manner of fouling, dirt and grime to be taken on and potentially disrupting the action - an oil reservoir lubricated each incoming cartridge to aid in its eventual extraction. As the Model 1937 offered only full-automatic fire, the speed at which the mechanism had to work was considerable, opening the door to failures/stoppages at every turn.
Feeding was from left-to-right of the receiver and by way of 20-round "clips" instead of a single ammunition belt. These clips were held in a tray (left side) and the feed mechanism pulled and oiled each incoming round and reinserted them into the clip after they were expended, pushing them through an awaiting tray (right side) - the thinking being that the strips could be reused (though individual empty shell casings still have to be removed from the clip manually). As such no true extraction system was needed in the gun but this had a way of complicating its operation some when compared to belt-fed contemporaries.
The original gun design had the Model 1937 used in tanks as a coaxial weapon and, therefore, there proved enough concern that spent shell casings could be sent into the turret's rotation system, jamming its drive controls. Hence the unique attempt to round the issue. Of course heavy sustained fire was out-of-the question and a gunner's assistant was required to consistently feed fresh clips into the ammunition tray for any sort of firing consistency.
Nevertheless, despite its inherent obsolete qualities, the Model 1937 proved itself an effective and surprisingly reliable weapon across the war years and saw production into 1943 and frontline service into the 1960s. The 450 round-per-minute rate-of-fire (200 being practical usage) allowed for good accuracy for an experienced gunnery crew as recoil was reduced (and barrel overheating better managed). Range was out to 5,400 meters with effective engagement falling within 1,000 meters - penetration from the large bullet was also rated as good. Even British SAS special forces elements operating in the North African desert thought enough of the machine gun to reconstitute captured examples for their own use.
A vehicle/tank version of the gun was also made as the "Model 1938" and this featured a more conventional 24-round count detachable box magazine fitted above the breech and other changes included a heavy-duty barrel for improved sustained fire and a more traditional pistol grip appendage at the rear of the receiver. Rate-of-fire of this product was increased to 550-600 rounds-per-minute. Some of this stock was later reconstituted for the infantry support role and sat atop tripods but retained their useful 24-round count boxes.
Portugal adopted the Model 1937 as the "Metralhadora pesada 7,92mm m/938 Breda" (note 7.92x57mm Mauser rifle chambering) and these were pressed into combat service during colonial actions.