Lewis Gun

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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.

History

The Lewis Gun or Lewis Automatic Machine Rifle was invented by Samuel MacLean and modified by the U.S. Army Colonel Isaac Newton Lewis in 1911, based on initial work by Samuel Maclean, but was not instantly adopted by the Americans. This may have been due to a clash of personalities with the American selection officer. It had a cyclic rate of approximately 550 rounds per minute. The gun weighed 28 lb (12.7 kg), only about half as much as a typical medium machine gun of the era, such as the Vickers machine gun, and was primarily chosen because it could be carried and used by a single soldier. The Lewis Gun was therefore more mobile than heavy machine guns and could much more easily follow the troops during advances and retreats, but it was still a bit heavy for its intended role. It was also relatively cheap at about one sixth the cost of a Vickers, and was issued in large numbers to soldiers serving on the Western Front. In total only 62 parts made up the gun (six Lewis Guns could be produced in the same time as a Vickers gun due to the excessive complexity of the Vickers lockwork). The lighter weight of the Lewis Gun made it popular as an aircraft mounted weapon, especially since the cooling effect of the high speed air over the gun meant that the radiator and cooling fins could be removed, making the weapon even lighter. Due to the fact that the Lewis gun started its firing cycle with no bullet already in the chamber, ready to fire (a so-called open bolt design weapon) it could not be synchronized to safely fire forward through an aircraft propeller.

Design

The Lewis Gun was gas operated. A portion of the expanding gases was tapped off from the barrel. This drove a piston to the rear against a spring. The piston was fitted with a vertical post at its rear which rode in a helical cam track in the bolt, rotating it at the end of its travel nearest the breech. This allowed the three locking lugs at the rear of the bolt to engage into recesses in the gun's body to lock it into place. The post also carried a fixed firing pin, which protruded through an aperture in the front of the bolt to fire the next round at the foremost part of the piston's travel.

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 perform perfectly 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.

Service

World War I

The British adopted it not long after the Belgians late in 1914. Each Lewis Gun required a team of two gunners, one to fire and one to carry ammunition and reload, and the whole rifle squad was trained to fire it in case the gunners were incapacitated.

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.

In 1917, the U.S. Army adopted the Lewis Gun in the .30-06 calibre, 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 (no small feat, considering the relaxed attitude toward weapon-cleaning among peasant conscripts). 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.

World War II

In World War II, it was replaced by the Bren gun for most infantry uses, but the Lewis saw continued service 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 airfield defence.

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.

Additionally, the German FG 42 borrowed significant design elements from the Lewis Gun.

The Lewis Gun was adopted by the USMC prior to its departure for the European Theatre in WW1.  When the Americans arrived, their Lewis Guns were taken from them and they were issued the worst automatic or machine rifle every forced on the long-suffering infantry, the French Chauchat in 8mm Lebel (and later converted to U.S. Cal. .30).  Army troops had a similar experience. 

The Chauchat was a long recoil-operated gun with a sedate rate of fire of 250 rounds per minute -- when it worked.  Ammunition was contained in a semi-circular magazine beneath the gun with two kidney-shaped slots so the rounds remaining could be counted.  THAT really worked well in the mud of the trenches.  There was only one thing that made the gun worse -- conversion to the more powerful American cal. .30 cartridge.  This conversion required a new magazine and capacity dropped from 20 to 16 rounds.  Relibility, never one of the Chauchat's strong points, got worse from more stoppages and parts breakage.  The Chauchat was quickly replaced by the M1918 Browning Automatic Rifle.  The French kept this miserable piece of ordnance in production from 1915 to 1924.

The gas operating principle of the Lewis Gun was incorporated into the U.S. Army's M60 General Purpose Machine Gun of the late 1950's that became the replacement for the .30 Browning machine guns in-service.  The M60 GPMG also incorporated the belt feed mechanism of the WW2 German MG-42 light machine gun.

For pictures of the Lewis, do a Google search on "Lewis Gun."