In an effort to find a more suitable and reliable Heavy Machine Gun (HMG) design chambered to effectively fire the 7.92mm cartridge, the Czechs worked through progressive machine gun developments in the decade leading up to World War 2 (1939-1945). There was the ZB vz. 50, which failed to produce the desired results, followed by the ZB vz. 52 (the weapons were recoil-operated and gas-operated, respectively). Trials of the ZB vz. 53 were had in 1934 which incorporated some improvements to the design and eventually led to the related ZB vz. 35 being selected for formal military service. Limited circulation followed.
From this work arose a new, improved design under the designation of ZB vz. 37 in 1936. Initial forms were delivered with a tripod support base with spade grips for infantry-level service. Then followed a vehicle-mounted weapon as the ZB vz. 37UV and this carried a full shoulder stock as well as pistol grip. The ZB vz. 37O was the third of three versions generated and this one intended for defense of fortified positions and, thusly, had a connection point for pintle mounting.
At its core, the weapon was an air-cooled, full-automatic-only system with gas-operation. The locking system relied on a tilting block arrangement. Chambering was for the 7.92x57mm Mauser rimless cartridge fed from a 100- or 200-count metal-link belt. Cyclic rate-of-fire reached up to 750 rounds-per-minute while muzzle velocity was rated at 2,600 feet-per-second - giving good penetration at range. Overall length was 1,105mm with a barrel measuring 678mm long. A conical flash hider was fitted over the muzzle and iron sights were installed along the top of the weapon forward and aft. Cooling fins detailed the barrel section as did a slotted forend.
The ZB vz. 37 was in practical use in the lead-up to World War 2 and Romania became one of the largest recipients of the Czech development followed by orders from China and Iran. Britain also moved on the product and eventually adopted it (through local production) as the classic "BESA" vehicle machine gun series. Other operators were seen in Afghanistan, Chile, Peru, Slovakia and Yugoslavia.
With the German occupation of Czechoslovakia, the gun-making facilities at Brno fell under German control so this meant that the machine gun was taken into service by the conquerors and appropriately re-designated to "Schwere Maschinengewehre 37(t)". In 1941, manufacturing of the weapon was relocated to Vsetin, however, the German need for their own standardized guns was such that Czech shops were forced to switch over to producing German products instead - this ultimately reduced production of the ZB vz. 37 series before the end of the war.
The weapon saw post-war service and large-scale production overall. A more simplified tripod was eventually introduced which replaced the original version - deemed unnecessarily complicated.