Sten SMG: Pinnacle of Simplicity

The Sten sits alongside the Thompson, M1 Garand and MP40 as the most famous and iconic firearms of the Second World War. Over four million were built across a vast amount of copies and variants.

Essentially a tube with a magazine, the Sten gun was the ultimate display of simplicity. It was built from less than 70 parts and could be made by small workshops with minimal experience.

It was copied many times and used all over the globe for decades after the war, cementing its position as one of the best firearms ever built.

Background

The Sten was an iconic British weapon produced early in the Second World War. As the conflict intensified in 1940, the British military confronted a critical shortage of small arms.

This crisis was made worse by the Dunkirk evacuation, where large quantities amount of British equipment, including weapons, was left on the beaches of France.

Naturally, there was a need for a new weapon, one that was cheap, easily manufactured, and could be built and supplied to Britain and its Commonwealth, as well as resistance movements in Europe.

Stocks of weapons and equipment left behind at Dunkirk.

The challenge was a big one. Britain’s industrial and economic resources were stretched thin by the demands of a global conflict, necessitating a solution that could exist within these limitations.

Britain had obtained significant numbers of Thompsons from the US, but these were hefty and expensive weapons that simply couldn’t be acquired in a big enough quantity.

A cheaper alternative was desired.

British soldier armed with the expensive M1928 Thompson submachine gun. These were expensive and in high demand.

The response to this challenge was spearheaded by Major Reginald V. Shepherd and Harold J. Turpin, who worked out of the Royal Small Arms Factory in Enfield. The MP28 and its British copy, the Lancaster, provided much of the inspiration for their new weapon.

As is clear now, the two prioritized simplicity, ease of manufacture, and functionality. Unlike its inspirations, creature comforts and lengthy manufacturing processes were discarded to make it as basic as possible.

They named their creation the STEN, after the initials of their last names, Shepherd and Turpin, and the “En” from the Enfield factory that built them. However the weapon is more commonly called the Sten.

The Lancaster submachine gun was a British copy of the German MP28. This one is fitted with a torch.

The engineering philosophy behind the Sten gun was predicated on the use of stamped metal parts. This approach drastically reduced the need for skilled labor and elaborate machining processes, allowing for smaller establishments to assist in their production.

Such simplicity also meant that the Sten could be produced at a fraction of the cost and time required for conventional firearms.

However, achieving reliability and user safety with such a simplified design presented its own set of challenges. Early models of the Sten were prone to malfunctions and required several iterations to refine.

Factory staff compare their old products, medals, with their new assignment of Sten guns. The Sten was so simple that small manufactories like this could produce it.

Design of the Sten

The gun consisted of a simple metal tube for a body, and a basic bolt assembly. Despite the aim of making a cheap and easy to make submachine gun, the first version of the Sten still incorporated wood furniture. However these were removed in later designs, where it became a truly simple weapon.

The Mark II Sten was made purely of metal, and had a simple tube and butt plate for the stock. Even the grip behind the trigger was merely a metal plate.

The Sten was extremely simple. Image by Grzegorz Pietrzak CC BY-SA 3.0.

One of the Sten’s main attributes was its extensive use of stamped metal parts. Stamping allowed for rapid production and assembly, as parts could be quickly cut and shaped from sheets of metal without the need for extensive machining.

This method drastically reduced manufacturing time and costs, enabling the production of millions of units throughout the war. Additionally, the simplicity of its design meant that the Sten could be easily disassembled and reassembled, facilitating maintenance and repairs even in field conditions.

The gun’s most distinct feature is its iconic side mounted magazine. It could 32 rounds arranged in two columns, and facilitated firing from a prone position more easily.

Diagram from a 1942 manual showing the Sten’s primitive construction.

The Sten operated on the blowback principle, firing 9mm Parabellum ammunition from an open bolt. This choice of ammunition was strategic, as 9mm was widely used, making it easier to supply.

The open-bolt design was integral to the Sten’s simplicity, reducing the number of moving parts and thereby the potential for mechanical failure. It could fire around 550 rounds per minute.

However, this design also made the weapon susceptible to dirt and debris, which could lead to reliability issues under combat conditions.

The Sten’s magazine well was susceptible to damage if used improperly. Image by Grzegorz Pietrzak CC BY-SA 3.0.

The magazine was another source of issues for the Sten. The 9 mm rounds have a slight taper, which meant they didn’t sit or feed very well through the Sten’s straight stick magazine. They were also prone to damage which could also cause feeding problems.

Contrary to what is often thought and seen, the operator was not meant to use the Sten’s magazine as a grip. This put stress on the magazine well and could, over time, cause the magazine to become loose and not feed properly.

Instead, the operator was meant to hold the Sten by the barrel shroud. Some weapons were given a fabric wrap to prevent burns. However, the gun could also be held by the lower receiver.

Sten Variants

The Sten was produced in several variants, from the Mark I to the Mark VI, each designed to improve upon or adapt the basic model to specific needs.

The Mark I had wooden grips underneath the receiver, and a vertical grip under the magazine which could be folded away when stowed. At the rear was a primitive metal stock with a wooden hand grip. Unique to this variant is a flash hider at the muzzle.

The Mark II is the most recognisable version of the Sten, and simplified the original design even further. This example was made entirely from metal, omitting the wood under the lower receiver and the folding foregrip.

The rearmost portion of the barrel was covered by a metal shroud with air holes. This enabled the operator to hold the Sten in this area without touching the barrel.

Further changes were made, including the removal of the flash hider, and stock that now consisted of a simple metal tube. Just behind the trigger, attached to the stock and receiver, was a metal plate that acted as a grip.

The Mark II introduced a folding magazine well, which could fold 90 degrees to face vertically down. The weapon could not be fired like this, it was added to make the weapon more conveniently shaped for stowing. This was the most produced variant of all, with over two million being made.

Over 4 million Stens were made in total.

A silenced version of the Mark II was produced, designated the Mark IIS. The Mark III simplified the design even more, reducing the parts quantity down to just 48. It can be identified by the barrel shroud that is nearly as long as the barrel itself. The Mark III lost of the flexibility of the Mark II, such as the rotating magazine well and removable barrel, so it was less popular.

The final variant produced on a large scale by Britain was the Mark V. It had a wooden stock and improved sights for better accuracy. A large number of other variants were made that are too numerous to cover here.

The Mark III Sten, with the extended barrel shroud. Image by MKFI.

Usage

The Sten gun was extensively used by British and Commonwealth forces throughout World War II, serving in every theater from the deserts of North Africa to the jungles of Southeast Asia and the cities and countryside of Europe.

Its lightweight and compact design made it particularly suited for airborne troops, who required easily transportable weapons for operations behind enemy lines.

One of the most notable aspects of the Sten gun’s operational use was its adoption by resistance movements across Nazi-occupied Europe.

Winston Churchill firing a Sten.

The weapon’s ease of concealment, combined with the ability to manufacture or repair it with limited resources, made it an ideal armament for partisan fighters.

It was smuggled into occupied territories through various means, including by air drops and shipments, significantly bolstering the capabilities of resistance groups. Also, the Sten fired the same round as the MP40 and other German weapons so ammunition was more readily available in Europe compared to others like the .45 ACP, fired by the Thompson.

The Sten gun was commonly used by elite units too, like the British Commandos and the Special Air Service (SAS).

The side-mounted magazine meant the Sten could be comfortably used while prone.

Despite its widespread use and significance, the Sten gun was not without its challenges and limitations. Its open-bolt design made it prone to jamming, particularly in harsh conditions where maintenance was difficult.

Additionally, it meant the weapon was capable of firing if knocked or dropped. However this can only occur if the weapon is left cocked, and is problem shared with all open bolt guns. The Sten incorporated a lock in the receiver to lock the bolt in place to prevent this.

Nonetheless, these issues were often outweighed by the weapon’s overall benefits, particularly its contribution to the mass arming of Allied forces and resistance groups at a critical juncture in the war.

Italian partisans armed with Sten guns. The weapon was very popular among resistance groups as they were easy to conceal, supply and keep maintained.

The weapon was imitated on a great scale. Australia, Germany, Argentina, Israel and many more made their own versions of this versatile firearm. The widespread use of the Sten gun illustrates its importance as a weapon of resistance, liberation, and tactical advantage.

Despite its simplicity and the constraints associated with its design, the Sten proved to be a versatile and effective tool across the globe.