The Lewis light machine gun was designed in USA by Col. Isaac N. Lewis, based on earlier machine gun by Dr. Samuel McLean, but found no takers because of personal opposition from US Army’s Chief of ordnance. Trying to sell the gun overseas, US-based Automatic Arms Co, which held patents for Lewis guns, established a subsidiary company in Belgium, know as Armes Automatiques Lewis SA. However, it was a pure marketing agent, and production contracts for first “European” Lewis LMG were placed in 1913 with British Birmingham Small Arms (BSA) company. First batch of 50 BSA-made Lewis guns was completed by mid-1913, in as much as seven different calibers, with obvious goal of marketing these guns across Europe. When war broke, BSA received orders for Lewis guns, and by the end of the war delivered well over 15 thousands of Lewis guns. In USA, Lewis machine guns were built in .30-06 caliber, mostly for US Army Air Corps and for US Marine corps. The Lewis gun also saw extensive use as an aircraft machine gun during WW1 and in following decade.
Lewis light machine gun became most famous in British use and manufacture; it was widely used by British troops during WW1 and afterwards. During WW1 it was also supplied to Imperial Russia. During WW2, many infantry Lewis guns were recalled from reserve stores and issued to British Home Guard units. Furthermore, in the view of possible German invasion in 1940-41, many former aircraft Lewis guns, of both British and US origin, were converted for ground use and also issued to Home Guard. It must be noted that ex-aircraft Lewis guns, supplied from USA through Lend-lease program, were chambered for .30-06 US Service ammunition; when converted to ground use in UK, these guns retained its chambering and were marked with red stripes to distinguish its non-standard chambering.
Lewis machine guns were also manufactured under license in Japan (as Type 92, for Naval infantry and aerial use) and in the Netherlands.
Lewis light machine gun is a gas operated, air cooled, full automatic only weapon that fires from open bolt. It has a non-removable barrel with aluminum radiator, enclosed into tubular barrel jacket of relatively large diameter; jacket was opened from both front and rear. When gun was fired, the muzzle blast caused the air to flow inside the jacket from rear to front, providing forced air cooling for a relatively light barrel. In aircraft versions the jacket and radiator usually were discarded to save weight.
The basic action used a rotary bolt with four radial lugs, located at the rear of the bolt; lugs locked into the recesses in receiver walls. Bolt was operated by a vertical stud, which entered a helical cut made in the bolt body. This stud was installed on the gas piston rod, which runs below the barrel. Gas block was located near the muzzle, and was concealed within the barrel jacket. One unusual design feature of the Lewis gun was the return spring. It was a spiral, clock-type spring which operated a gear wheel, located in the semi-circular hump below the receiver. The gear wheel co-operated with a teethed rack, machined on the underside of the gas piston rod, so the return spring was wound upon recoil cycle (under the power of powder gases), and then unwound itself on closing movement of the bolt group. The firing pin was fixed to the vertical stud on the gas piston rod.
The feed system of the Lewis gun was also somewhat unusual, as its flat pan magazine, which held rounds in two layers, had no spring to feed cartridges into the gun. Instead, the magazine was powered by the gun itself, via special feed operating arm with two pawls, which engaged stamped ribs, made on the outside of the magazine cover. The feed arm oscillated in horizontal plane, being operated by the vertical stud located at the rear of the bolt. With each cycle of the bolt group, magazine was rotated by one step to feed next cartridge into the ready position. For aerial combat, four-layered magazines with bigger capacity were produced.
Standard furniture for Lewis light machine gun included a wooden pistol grip and a wooden buttstock, and a folding, detachable bipod. Optional carrying handle could be installed near the center of gravity of the gun, that is, at the rear of the barrel jacket.
Guns, converted from aerial to ground use often lacked the barrel jacket and radiator; a light bipod was attached to the mounting, originally used to install the gun in aircraft turrets. Additionally, a skeleton buttstock was pinned to the rear spade grip and a simple rear sight set to 400 yards