The UK's Sterling Submachine Gun Part 1: Historical Lookback

Early in World War II, facing the distinct possibility of invasion, the UK armed forces were desperate for weapons, purchasing wherever possible. Domestic arms makers were operating at full capacity as well. To arm Home Guard personnel, special units such as the airborne, tank crews, and others, the submachine gun seemed an attractive option. Its manufacture required fewer scarce materials, in many cases less machining, and less expensive ammunition if chambered for the 9x19mm cartridge. The SMG would also require less intensive training than the SMLE rifle. The Thompson SMG was already in use with the Commandos, but it was heavy, expensive, and those on order from the USA were already allotted to other units.

The first UK SMG produced during the War was the Lanchester, a copy of the German MP28. Unlike SMGs that would follow it, the Lanchester required precision machining. In any case, the Royal Navy had already spoken for most of its production. Developed simultaneously was a far more inexpensive solution—the famous Sten Gun.

Requiring only 47 parts, most of which were stampings, the Sten could be produced quickly and inexpensively in small workshops. More sophisticated machine shops could produce the bolt and barrel. Many other parts were stampings, which had the advantage of requiring less steel—far less waste from machining would occur. The Sten was also chambered for the 9x19mm Parabellum cartridge, thus, requiring less lead, less jacketing metal, and less brass than the Thompson’s .45 ACP cartridge.

Another advantage, especially for units that would be operating in occupied Europe, the 9mm Parabellum round was standard issue in the German Army allowing captured ammo to be used. As a result, the Sten was dropped in substantial numbers to European Resistance units. In fact, some resistance units built their Stens in bicycle shops or garages.

During the course of World War II, improvements in the design of the Sten resulted in various “Mks.” The Mk I was replaced relatively soon by the Mk II, more than two million of which were produced. An advantage of the Mk II was that it could be suppressed and saw clandestine use not just throughout World War II, but also through other conflicts to Vietnam and even later. Other Mks followed the Mk II. The Mk III used fewer parts than the Mk II and employed many stampings. Though the Mk II and Mk III remained in service simultaneously, units avoided issuing both as many parts were not interchangeable. The Mk III also had a reputation for being less reliable. Mk IV versions were experimental. The final version of the Sten Gun, the Mk V, added a mount for a bayonet and a wooden pistol grip and stock. An interesting feature was the inclusion of a No.4 Lee-Enfield rear sight.

Eventually, more than 35 countries would use some version of the Sten. Despite the German use of famous SMGs such as the MP38 and MP40, the Wehrmacht also used captured Stens. In fact, the Germans also made their own copy of the design.

The Sten was “of its time”: it was produced quickly and inexpensively, when the British were fighting for their existence. However, it was not always popular with British troops, who labeled it the “Plumber’s Abortion” or the “Stench Gun.” The retention of the same magazine feed system from the German MP28 and Lanchester,” which merged cartridges from two columns to a single column to feed, invited problems when dirt entered the magazine, or its lips were dented or otherwise deformed. This resulted in a reputation for unreliability by the Sten. The Sten’s safety system, once again inherited from the MP28 and Lancheser, relied on rotating the bolt into a slot in the receiver to put it on safe. Should the bolt get jarred out of the slot a negligent discharge could result.

Despite its faults, the Sten had been available during Britain’s “Darkest Hours.” While the Sten remained in service, design and testing of a much-improved SMG, the Sterling, had begun. George Patchett filed his initial patent on what would become the Sterling SMG in August 1942. Key components protected by this patent were the trigger and selector mechanism that allowed the weapon to fire in either semi- or full-auto modes. Some elements of the Patchett design were influenced by the Lanchester SMG produced prior to the Sten.

These included: the perforated barrel shroud, side feed magazine, and the chamber, which allowed use of a variety of 9mm ammunition. On 25 September 1942, the Patchett was demonstrated to the Army Ordnance Board. It proved reliable, but it lacked a stock and sights. Reportedly, there were also questions about the strength of its end cap.

Patents were filed in May 1943, for a collapsible stock. By this time, front and right sights had also been added to the design. During development, the Sten’s 32-round magazines were used because of their availability though the problems of a double feed magazine transitioning to single feed remained. The most promising event for the Sterling’s future occurred in January 1944, when the War Office issued a bid spec for a new “machine carbine.”

As a result, Patchett was awarded a contract for 20 prototypes for further testing. However, the Patchett design faced tough competition as BSA (Birmingham Small Arms) also had a machine carbine in development. Actually, BSA had developed an SMG designated the Welgun in 1942 for the SOE (Special Operations Executive); the intended use was to supply European resistance movements (a niche filled by the Sten) hence the Welgun never went into production. BSA had the advantage of proven ability to deliver, having produced over 400,000 Stens during the War. In Sterling’s favor, the company had produced almost 75,000 Lanchester SMGs.

During trails in 1947 and 1948, the Patchett seemed to be losing out to BSA because of problems during mud testing. Patchett, chief designer at the Sterling Armaments Company, had been involved in production of the Lanchester SMGs during the war, and thus had access to the resources of that established firm. Though problems continued with the Patchett design, the War Office issued new specs for the “machine carbine” in October, 1948, which included an adjustable 50–200 meter rear sight and a mount for the No.5 Mk. I bayonet. A new dual return spring design from Patchett solved most of the Patchett’s reliability problems. Also aiding the Paatchett’s reliability was a new double column magazine employing a roller platform and curved body designed by Patchett in 1946.

It should also be noted that the Sterling employed the API (Advanced Primer Ignition) Blowback type of action. With this design, the primer ignites while the bolt is still moving forward, prior to the cartridge being fully chambered. In simple terms, the advantages of the API system are allowing use of a lighter bolt and reduced felt recoil when firing, especially on full auto. Another noteworthy feature of the Sterling’s bolt is its helically grooved surface, which helps remove debris and fouling from the interior of the receiver, thus enhancing reliability.

Without going into all the details, trials continued until late in 1950 with no decision about a new SMG for British armed forces. By early 1951, the Danish Madsen M50 appeared to offer more competition for the Patchett than the BSA. As a result, firing tests of 10,000 rounds were carried out of the Patchett, Madsen, BSA Mk III, and Australian MCEM-2 in May 1951. The BSA Mk III and Australian MCEM-2 did not perform well. The Madsen M50 and Patchett did perform well, with the Patchett receiving only one minor criticism: the magazine’s lips needed to be strengthened. The Patchett drew special praise for its accuracy. The Ordnance Board recommended immediate adoption of the Patchett.

Nevertheless, additional trails were held in October 1951, the BSA Mk III and Madsen M50 redesigned weapons again taking on the Patchett. During 10,000-round-endurance testing, the BSA suffered 46 malfunctions, the Madsen 44, and the Patchett only 6. Using the point system developed for the trials, the Patchett scored twice the number of points as the BSA. A year later, in October 1952, the Ministry of Supply ordered 300 Patchett Mk II SMGs for troop trials. These SMGs were supplied to various British units including some deployed to the Korean War. Another order for 300 SMGs for additional troop trials was received by Sterling in July 1953. Additional “trials” ordered continued into 1954, with responses from the troops overwhelmingly positive about the Patchett when compared to the Sten. In February 1955, the improved Patchett Sterling was adopted as the “Sterling SMG 9mm Mk III” (Gun, Sub-Machine, 9mm L2A2). The name was officially changed from “Patchett Machine Carbine” to “Sterling Sub Machine Gun” at this time. However, it was the “Gun, Sub-Machine 9mm L2A3” (AKA Sterling Sub-Machine Gun, 9mm Mk4), adopted in September, 1955, that would remain the principal SMG for British troops for almost 40 years.

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