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BSA Light Infantry Pattern Lewis Machine Gun

Though reasonably unusual, even by comparison to the light machine guns of WW II, I consider the Lewis gun as probably the first true practical LMG. In WW I it armed not only the British infantry sections, so giving them a reasonably light and portable firebase weapon, but it was also used by the Royal Flying Corp. It was then used extensively in WWII; again in a number of roles, from arming the Home Guard, armament on all sorts of vehicles and as an anti aircraft defence for the Merchant and Royal Navies.

The history of the design can be traced back to one Samuel McClean who in 1910 designed a rather complex machine rifle, he assigned all the mechanical patents to The Automatic Arms co. of Buffalo, New York. Technically the gun was a non-starter and quickly rejected by the US Board of Ordnance after brief trials.

Automatic Arms now desperate to recoup some money turned to US Army Colonel Isaac Newton Lewis asking him to re-work the gun into something a deal more practical. Lewis maintained the basic operating mechanism, which consisted of an adjustable gas flow and piston design, that cammed a rotating bolt in and out of engagement. He added the distinctive flat (pan type) magazine and an integral cooling system that turned out to be near redundant, though that was not discovered until many years later. He also took a very different approach to the type and location of the main spring of the gun - as we shall see.

US Rejection

Now named after him, the Lewis Gun was offered up for trials again, but once again -although vastly improved into a practical LMG for its day - the Lewis did not get the nod from the US Army. Despite a demonstration of it being fired from a Wright Type B biplane on June 7th 1912. This is said to be the first time a machine gun was fired in manned flight. The US High Command was less than impressed by what they doubtless saw as a stunt; saying that aircraft were only good for observation and scouting and not as a platform for aerial gunnery…  How times change!

The upshot was that Lewis, disappointed by his countrymen’s short-sighted attitude left the USA to sell his gun elsewhere. He in fact called the US Ordnance Department “ignorant hacks” for their rejection of his design.

History tells us that Lewis did this same thing again in England in November 1913 at of all places Bisley Camp. Here a Lewis was fired from a Grahame-White airplane by a Lieutenant Stellingwerf of the Belgium Army. This time it would appear that the powers that be were impressed with the design and its ability, so assuring its continued success. Try that these days and I’m sure the NRA would not be impressed…

However, before this event Lewis went to Belgium (in January 1913) and found a much warmer reception than he had received in the USA. After these demonstrations the gun was adopted in 303 British calibre and not the 30-06 Springfield of which the trial guns were chambered in. Original manufacture was by the Armes Automatiques Lewis. This comprised of a syndicate that acquired the patent rights to the Lewis for Europe and the whole of the eastern hemisphere.

The BSA Connection

The syndicate had decided to have the separate parts of the gun manufactured by different companies in Belgium then assembled at a central factory. How Birmingham Small Arms came on the scene was quite by chance. Lewis was visiting England to try and overcome some barrel manufacture problems the gun had encountered and approached BSA to make 100 special barrels.

BSA inspected the Lewis and found it to be good, then they applied for the sole manufacturing rights of the design and syndicate which was agreed. Straight away BSA’s experimental department was placed at Lewis’s disposal and as they say the rest is history. With guns being made at both of their Birmingham plants.

The Lewis’s first baptism of fire came in 1914 in the retreat through Belgium and at that time the allocation of guns was small, with just three per battalion. By 1916 and the battle of the Somme this had been upped to one per platoon with a dedicated 8-man section commanded by an NCO. And it’s estimated that by that year over 50,000 guns had been produced. By 1918 this had been raised to two per platoon.

Despite its air service use, the Lewis, as I already said, gave the British section/platoon a very effective light automatic weapon, which offered flexible firepower. For in comparison to the German Maxim 08 and our own Vickers heavy machine guns the Lewis was a true LMG; albeit a bit on the heavy side. Plus in terms of time, effort and cost you could make six Lewis’s for a single Vickers Gun.

It would appear that the Lewis was also appreciated by the Germans, who had no true LMG, though they did have the lightened version of the Maxim 08, the 08/15, which weighed a mere 43 lbs. Contemporary reports show that when ever possible the Germans would pick up Lewis’s from the battle field and press them into their own service, due to their light weight and sheer usability. It seems that their famous Storm Troops were particularly enamoured of the gun, which fitted in very well with their tactics. So much so that German machine gunners were actually taught about the Lewis.


The Lewis Gun is a distinctive weapon both visually and mechanically. Most obvious is the large barrel jacket that extends a few inches in front of the muzzle, likewise the flat pan magazine on top of the action. Also is the fact that it uses a wind-up, clockwork-style spring just in front of the trigger to provide the energy for the return stroke.

Looking at the mechanism shows a reasonably conventional gas and piston system. The Gun fires from an open bolt, in that the breech block is held to the rear prior to and after firing once the trigger is released. Pressing the trigger allows the block to go forward and rotate into battery, and as it shuts the firing pin is automatically moved to fire the cartridge. The action locks at the rear and mechanically is not dissimilar to that of the Swiss Schmidt Rubin straight-pull rifle.

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The gas tube is underneath the barrel with a basic regulator at the end to allow the gun to be adjusted to give reliable operation. A rate of fire of 500-600 rounds per minute is quoted by most sources.

The breech block sits on a post above the piston. The underside of the piston rod is toothed, which engages with a toothed wheel (pawl) with the clockwork spring inside it. As the gun fires the gas forces the piston rod rearwards, which has the effect to wind the coil spring, so generating energy for the return stroke. Feed is from the 47 round pan, with the cartridges in a two layer helical path. This is actuated by a feed arm that is powered by the piston cycling. It is said that feed is 100% no mater how the gun is angled up or down. Here everything is mechanically fed, with no springs as you would find in say the box magazine of a Bren Gun.

On the subject of feed the air service guns used a larger 97 round pan and there was also an attempt to make a true machine rifle variant (Light Infantry Pattern Lewis Gun) with no cooling jacket and a 22 shot pan. This weighed only 17 lbs when compared to the all up weight of 33 lbs with the jacket and 47 round magazine. Although light by comparison to a Vickers or the German 08/15, the Lewis was still a large and heavy gun. Its contemporaries were the French Chauchat and the American 1918 BAR (Browning Automatic Rifle).

On the point of the US involvement with the Lewis gun it did not come till much later. They were briefly used in 1916 in .303 British chambering by General Black Jack Pershing’s expeditionary force who chased Pancho Villa up and down the Mexican border. But with two years of battle success the gun was finally, if somewhat grudgingly adopted by the US as the 30-06” Calibre Lewis Machine Gun. These were manufactured by The Savage Arms Co. of Utica, New York. It would seem that the guns did show some early problems as they were chambered in 30-06 Springfield. But they were perfected and later used by the US Marines and the Army Air Corp with good success.


The bulbous barrel jacket was one of the gun’s unique features. The idea used a forced draught cooling system. The barrel was surrounded by a finned aluminium radiator, over which the jacket fitted. This left longitudinal slots for the air to circulate. On firing the depression at the muzzle caused by the burning powder was supposed to drag cold air in from the back end to keep the Lewis cool. BSA tells us that during the first few hundred rounds the temperature rises to 330? F. After that it rises to 440? after 1000 rounds, but doesn’t rise above that. The idea is that the aluminium conducts the heat away from the steel barrel fast. It also means that the jacket gets very hot, very quickly and it would be a stupid gunner who used it as a hand hold…

Frankly I believe that the whole concept was a waste of time and materials, with the gun weighing a lot more than it had to. This is born out by the fact that this system was never used again, nor do we see it today. More damning evidence is the Light Infantry Pattern gun, which had no such cooling system. Likewise the air pattern guns show a smaller jacket, with the later ones having none at all, so you can clearly see the over and under barrel/gas piston build.

The placement of the return spring under the action allows the Lewis’s build to be quite flexible. The butt is removable and a simple spade grip can be substituted. A bipod can be fitted to the barrel jacket, as can a carry handle. Sights consist of a rear flip up ladder, with micrometer-adjustable aperture; not unlike the later Bren Guns. The foresight is a windage-adjustable blade that clamps around the jacket.

A special anti aircraft sight was also available. The front was a big grid with an eye-shaped central bar system, the rear was just a big aperture that sat atop the back sight.

The air service Lewis’s were mounted above the top wing of most early fighter biplanes, prior to the adoption of the interrupter gear that allowed for a belt-fed Vickers gun to be placed on the engine cowling and fire through the propeller. Though quite often they were still retrained afterwards on planes like the SE5A and Sopwith Camel. The gun sat on a quadrant mount that allowed it to be pulled down by the pilot for reloading. I would imagine that they would be quite useful for firing up and forward if approaching an enemy plane or airship from below and behind?

However, the majority were used in the two seaters and placed in the observer’s position on a Scarfe ring mounting. These could be either single or double mounts and were fitted with a ‘wind vane’ sight to allow the gunner to compensate for elevation and deflection on their fast moving target. Generally the sights on these guns consisted of a large ring with a central pipper at the back and a simple blade or tall pin at the front.

With the air guns feed was always the larger 97 round drum. There’s a story about a fighter pilot who brought his Lewis down from the top wing to reload it and lost control of his aircraft. He suddenly found himself upside down hanging off the magazine, which luckily for him had stuck. History doesn’t tell us if he managed to get back in the cockpit…

Muzzle Heavy

In use the Lewis is a very muzzle-heavy design; hardly surprising given the extra weight and length of the barrel jacket and radiator. This however, makes it very controllable and therefore recoil friendly. There is also a modicum of moderation offered by the open end of the jacket, so it’s not as noisy as say a Bren.

The magazine is placed on the post on top of the action and locates by a spline. The cocking handle is pulled rearwards and the gun is now ready to fire. Pin point accuracy is not a real prerequisite of an LMG and you get the classic feel of the change of weight as the breech block and piston slam forward, as you do on the Bren or BAR.

One of the gun’s apparent weaknesses is the magazine, which is open underneath, so in combat, you could expect to get a lot of dirt on the exposed cartridges, which could lead to stoppages. Reading after battle reports tells two stories, some say the Lewis was very reliable, others that it was prone to all sorts of stoppages; especially the main spring breaking due to excessive heating. I would say the last was possibly true as the loading on a coil type spring, is probably more intense than a longitudinal coil type.

As an ex-soldier I believe that a gun should be well maintained and understood by its user and in that way the amount of stoppages will be reduced by experience and professionalism. The Lewis action lived on in some ways as a similar gas/piston mechanism was used for the German FG42 paratrooper rifle and the US M60 GMPG uses a similar system too.

Its weaknesses aside, which I believe were few, the Lewis proved to be the right tool at the right time and I’m sure was well appreciated by the troops that used it…