The Lewis Gun is a pre-World War I era squad automatic weapon/machine gun of American design that was most widely used by the forces of the British Empire. It was first used in combat with the Belgian Army in World War I, and continued in service all the way through to World War II. It is visually distinctive because of a wide tubular cooling shroud around the barrel and top mounted pan magazines.
It was designed with an aluminum barrel-casing to use the muzzle blast to draw air into the gun and cool down the internal mechanism. There is some discussion over whether the cooling tube was effective or even necessary. In the Second World War many old aircraft guns which did not have the tubing were issued to anti-aircraft units of the British Home Guard and to British airfields, and were found to function properly without it. Later, more aircraft guns were used on vehicle mounts in the heat of the Western Desert and again did not suffer without the tube. The Royal Navy however, insisted all their Lewis Guns had to retain the tubing, even in the cold of the Arctic.
The Lewis Gun utilized two different drum magazines, one holding 47 and the other 97 rounds (the picture below shows the 47 round version). The 97 round magazine was designed for aircraft use and was considered too heavy for infantry use. A few Lewis Guns were issued for anti-aircraft use with the 97 round drums by the British Army in 1916, but the big drum did not stand up well to the arduous conditions of trench warfare and the 47 round was used thereafter. The aircraft type of magazine had to be carefully stored when used with ground mounts as the underside was open and exposed the ammunition to dust, dirt or spray, which was then carried into the gun mechanism. Interestingly, the Lewis was considered very reliable despite this design fault, but then this may have been in comparison to other less reliable designs like the notorious Chauchat. Unlike other drum magazine designs, the Lewis' drum was not wound against a spring but was mechanically driven by a cam on top of the bolt which operated a pawl mechanism via a lever.
An interesting point of the design was that it did not use a traditional longitudinal coiled spring, but used a spiral spring, much like a big clock spring, in a semi-circular housing just in front of the trigger. The operating rod had a toothed underside, which engaged with a cog which wound the spring. When the gun fired a round, the bolt recoiled and the cog was turned, tightening the spring until the resistance of the spring had reached the recoil force of the bolt assembly. At that moment, as the gas pressure in the breech fell, the spring unwound, turning the cog, which, in turn, wound the operating rod forward for the next round. As with a clock spring, the Lewis Gun's recoil spring had an adjustment device to adjust the recoil resistance for variations in temperature and wear. Unusual as it seems, the design proved enduringly reliable.
Colonel Lewis became frustrated with trying to persuade the U.S. Army to adopt his design. He retired and headed for Belgium much like John Moses Browning. The Belgians quickly adopted the design in 1913, using the .303 British round. Not long after that the Birmingham Small Arms Company (BSA) purchased a licence to manufacture it. The Germans first encountered the Lewis in 1914 and nicknamed it "The Belgian Rattlesnake".
The early British Mark IV tanks used the Lewis Gun. It was used on British aircraft either as an observer's or gunner's weapon or as an additional primary weapon to the more common Vickers machine gun. Due to its open bolt firing cycle, it proved to be impossible to synchronise it to fire through a spinning propeller, so that the heavier Vickers gun had to be used for this purpose. Because of this, the Lewis was fitted on S.E.5as above the top wing in a Foster mount, which was outside of the propeller's arc, and allowed the gun to be swung down on a rail to allow the magazine to be changed in flight. For the use of aircraft gunners, the Lewis was mounted in a Scarff ring, which allowed the gun to be rotated and elevated whilst supporting the gun's weight. The Lewis has claim to being the first machine gun fired from a plane.
In 1917, the U.S. Army adopted the Lewis Gun in the .30-06 caliber, but the design was soon replaced in September 1918 by the Browning Automatic Rifle.
The Russian Empire bought significant number of Lewis Guns in British .303 or Russian 7.62x54R calibre and used it as squad automatic weapon for infantry units, or as GPMG for cavalry, cossack, or dragoon units. These guns were replaced by the Degtyarev light machine gun from the late 1920s. The Lewis had reputation of being a somewhat cumbersome, but fairly reliable weapon. Some Lewis Guns were briefly re-issued in Autumn 1941 to make up for losses of equipment to the advancing Germans. They were withdrawn from service in 1942-1943, as more DPs became available.
The Germans also used captured Lewis guns (rechambered for German rounds) after the Battle of the Somme. The Lewis remained in use in these units until the formation of the Maschinen-Gewehr Scharfschützen battalions, in April 1918. However, the stormtrooper battalions seem to have liked the Lewis gun so much that many retained them in preference to the later light machine guns produced by the Germans. Lewis guns remained in frontline service until the end of the war, with captured weapons repaired and converted in a factory in Brussels.
The French Air Services (L'Aeronautique Militaire) used many Lewis Gun (in .303 caliber) as an observer's gun fitted on a Scarf ring. They were actually manufactured in France under licence by the firms of Milde and Darne.
In World War II, it was replaced by the Bren gun for most infantry uses, but the Lewis saw continued service on Royal Navy warships and submarines. Additionally, it was used as a vehicle-mounted weapon, primarily as a side gunner's weapon on aircraft. Although it was probably obsolete for that role as well, the British were facing something of a major economic crisis during the war, and had to use their existing stocks of Lewis guns for purposes such as defending airfields.
In the crisis following the Fall of France, Lewis guns were used to arm the British Home Guard.
After World War II, the Lewis was officially discontinued in British Service, and all existing models were retired in favour of the Bren, Vickers and other machine guns.
The Lewis gun saw limited use with American forces at the beginning of World War II. The United States Navy used Lewis guns on armed merchant ships, small auxiliary ships, landing craft, submarines, and for ships' landing forces. The 4th Marine Regiment and Philippine Army units used Lewis guns against the Japanese after the invasion of the Philippines in 1941.
Additionally, the German FG 42 borrowed significant design elements from the Lewis Gun.