Silenced Sten Gun

During the fall of 1941, amidst the urgent demands of World War II, innovative adaptations to existing weaponry are considered to meet the needs of covert operations by both the Special Operations Executive and the regular army. One such adaptation involves the Winchester Model 94 rifle, a lever-action rifle chambered in .30-30 Winchester caliber. With a supply of 200-300 rifles already available in England, the plan includes equipping these with Cochrane Barnett night sights for improved accuracy in low-light conditions. Additionally, Parker Hale is tasked with producing Maxim silencers to enhance the stealth capabilities of these rifles. To complement the silencers, handloaded ammunition is required to achieve subsonic velocities, essential for maintaining a low auditory profile during operations.

In parallel, there is a proposal to modify a number of Martini Henry carbines in .577/450 caliber. These rifles are to be outfitted with silencers and adapted to use smokeless powder ammunition, which would further reduce their firing noise and smoke emission. Alongside these adaptations, a small batch of Luger pistols is equipped with Parker Hale-type silencers. Although it remains unclear whether these silenced Lugers are ever officially issued, some examples still exist today, highlighting their role in the experimental phase of weaponry development.

Silencers

The demand for silenced submachine guns continues to escalate, prompting further innovations. The Sten Gun, particularly the Mark II model known for its easily detachable barrel and shroud, becomes a focal point for these efforts. By the summer of 1942, the development of a silencing unit for the Sten is underway. The initial tests of these silenced Sten guns, along with silenced Thompson submachine guns, are promising. These tests focus on reducing the sound and flash signatures, achieving precision at 200 meters, and ensuring penetration at 300 metres. The silencers for the Sten guns are manufactured by Enfield, while those for the Thompson guns are produced by J. Armstrong & Co.

These adaptations are part of a broader strategy to equip Special Operations Executive agents and regular army units with weaponry that can operate effectively and discreetly behind enemy lines. The development of silenced firearms is crucial in minimizing the risks of detection during sabotage missions and engagements in occupied territories, thus enhancing the overall effectiveness of Allied covert operations during the war.

Silenced submachine guns, designated as Special Sten and Special Thompson, are under evaluation, with the Sten receiving more favorable feedback. During testing, all Thompson silencers burst, whereas the Sten silencers remain functional after completion. The term “Special Sten” is officially adopted for this variant.

These prototypes, with their 56 centimetres long silencers, are cumbersome and not ideal for combat. They include a lightened bolt essential for operation, as their ventilated barrels diminish ammunition power. It is probable that this silencer was designed by Polish Lieutenant Kulikowski for the Special Operations Executive. A similar silenced Thompson is also part of this collection. While testing in England was ongoing and before any model received official approval, the Special Operations Executive began distributing silenced Sten guns in small batches to agents and resistance groups. In September 1942, the Special Operations Executive received a delivery of 110 silenced Stens. The distinctive rattling of the silenced Sten’s bolt was problematic, and despite efforts, this noise could not be sufficiently suppressed. Contrary to rumors, the use of bronze bolts, chosen for cost-effective mass production rather than noise reduction, did not relate to the silencer’s function.

Multiple organisations participate in the development of silenced Sten variants. The regular army keeps a close watch on this project, with The Small Arms Group of the Ministry of Supply Armaments Design Corporation taking charge of what eventually becomes the Sten Mk. II (S). The Special Operations Executive, under more immediate pressure, tests numerous silencers. Further tests in October and November of 1942 involve silencers designed by both the Chief Superintendent of Armament Design (C.S.A.D.), working on army units, and the Chief Inspector Small Arms (C.I.S.A.), focusing on Special Operations Executive units. A variety of silencers are evaluated. Ultimately, tests on Thompson silencers are halted in favour of concentrating on the Sten Gun silencers, aiming to develop a single model that integrated the best features of the prototypes for easier production, though this goal was not fully achieved.

By January 1943, a new batch of silencers is completed, and webbing hand guards are introduced to protect operators from burns caused by the asbestos-wrapped silencers. During this period, tests on the compact Welgun and Sten Mk. IV submachine guns, some silenced, are conducted. The decision is made to avoid adopting new designs into service where possible, and only a few models of these new designs were produced.

Throughout 1943, testing of the silenced “Special” Stens continues, and small batches are deployed for various operations across Europe. A model from Chief Engineer Armament Design is eventually chosen as the official Sten silencer for the British army. This period also sees experiments with lighter bolts and shortened recoil springs.

Sten 9 mm Machine Carbine Mk. II (S)

On January 31^st, 1944, the designation Sten 9 mm Machine Carbine Mk. II (S) is officially adopted, moving away from the previous “Special Sten” nomenclature to Mk. II (S). With the “S” standing for Special Purpose, not suppressed or silenced.

In July 1944, the Director of Infantry communicated with the Director of Artillery, Small Arms, about the use of two similar silencing units for Sten guns. It is noted that “Attachment no. 6, Sten Machine Carbine, Mark 1, design E.S.6 (W.D.),” not approved for army use, is still present in army stores. The E.S.6 (W.D.), a designation for an Special Operations Executive silencing unit makes at Special Operations Executive Station XII, is procured separately by the Special Operations Executive, despite the army’s adoption of a different model. This is due to the Special Operations Executive’s urgency and unwillingness to wait for the army’s final decision. By March 1945, the use of the army-approved silencing unit ceases, with production shifting entirely to the E.S.6 (W.D.) model.

A significant challenge with silencing the Sten guns is the occurrence of double taps or runaway guns, caused by the silencers reducing the power of the ammunition to the extent that the bolt does not retract enough to engage the sear. This issue also affects regular Sten guns. Initially, the British 9 mm Mk. Iz ammunition, adopted in December 1941 with a 115 grain bullet at 365 metres per second, proves too weak for reliable operation of the Sten. To improve reliability, the Mk. IIz cartridge is introduced in September 1943, using the same bullet weight but increasing the muzzle velocity to 396 metres per second. This change somewhat alleviated reliability issues but makes silencing more challenging. Silenced Stens are intended primarily for single shots, although they retain full-automatic capability for critical situations where such fire could save lives or complete the mission, but it is emphasised that this will quickly impair the silencer.

Sten Mk. II (S)

The Sten gun’s design involves igniting the primer with the firing pin as the cartridge stops against the chamber shoulder just before the bolt completes its forward movement. This mechanism uses some of the chamber pressure to stop the bolt’s forward motion. Early silenced versions with ventilated barrels required lighter bolts and recoil springs for functionality. The E.S.6 (W.D.) SOE design incorporates a deeper chamber, enabling the bolt to make contact with the breech end of the barrel before firing, thereby using the full chamber pressure to push the bolt rearward. This design allows the use of standard bolts and springs in the silenced Stens and theoretically enables any Sten Mk. II to be equipped with an Special Operations Executive silencing unit, though reliability issues remains with these adaptations.

Three primary models of the Sten Mk.II (S) are noted in substantial numbers:

1. First Production Model:
   • These silencing units are identified on B.S.A.-manufactured guns, with serial numbers in the series B 341000, B 360000, and B 363000.
   • The silencers, approximately 5 cm in diameter, lack web handguards, featuring integrated insulation between the inner and outer tubes.
   • The weapons display an “S” stamped on the magazine housing bottom and are marked STFN, likely due to a worn marking die.
   • The silencer contains metal discs at the front of an approximately 18.3 cm ventilated barrel with 6 bleed holes. A thick rubber disc at the muzzle end prevents powder gas escape, its effectiveness decreasing as the disc wears.
   • Serial numbers on the silencing units range from 1 to 3400, with numbers up to 1500 frequently observed, suggesting a possibly complete range. Some of these guns come equipped with night sights, typically within the 1-350 serial range, though one exception near 3400 exists, predominantly used by SOE agents.
2. Second Production Model:
   • Found on guns with “TF” serial prefixes, these units have about 3.8 cm diameter and are wrapped in asbestos string under a web handguard.
   • Unlike the first model, this one utilizes baffles instead of metal discs, held in place by a large threaded front cap on the muzzle, which can be unscrewed for maintenance.
   • A felt disc inside the muzzle cap helps seal the gases. The barrel, about 9.2 cm long, includes 10 bleed holes.
   • The guns and silencing units are matched by number, typically marked STEN Mk. II S, representing the official British army Sten Mk. II (S) as documented in military literature.
3. Third Production Model:
   • Manufactured by Fazakerley with “FP” serial prefixes, this model mirrors the first but has a 3.8 cm diameter and can be disassembled via a collar about one third from the rear.
   • It features the same disc pattern internally as the first model, with additional thin mesh discs at each end.
   • The barrel length is approximately 12.1 cm and includes 6 bleed holes.
   • These units also feature asbestos string insulation, covered by insulating tape. Unlike previous models, these Sten guns bear no special markings on the magazine housing.
   • Visually similar to the Army’s Sten Mk. II (S), they are designated “Attachment no.6, Sten Machine Carbine, Mark 1, design E.S.6 (W.D.).”

While these models differ in specifics, all silencing units share a similar design pattern: they range from 33 to 35.5 centimetres in length and 3.8 to 5 centimetres in diameter. Each is directly attached to its respective Sten Gun, replacing the standard barrel and shroud of a regular Sten Mk. II. The first and second production models are specifically matched to their guns, while the third model can theoretically be used on any Sten Mk. II.

Estimating the production numbers for the various models of Sten gun silencing units is challenging. It’s noted that the first production model appears in serial numbers ranging from 1 to 3400, though it’s possible only specific blocks within this range are actually used. The second production model, the standard STEN Mk. II (S), is estimated to have been produced in quantities between 2,500 and 6,000. The production details for the third model are less clear, similar to the first; these models are seldom found outside of Norway, where they are predominantly supplied by the Special Operations Executive. A reasonable estimate suggests that between five and ten thousand silenced Mk. II Sten Guns are produced in total.

Sten Mk. V

The barrels are short and ventilated to decrease muzzle velocity to approximately the speed of sound, enhancing sound reduction effectiveness. Silenced Sten guns significantly reduce sound signature and eliminated muzzle flash. A small number of Sten Mk. V submachine guns are also trialed with silencers, complicating matters as these had the front sight on the barrel. A special clamp with an integrated front sight is developed for the Mk. V (S), which used the Mk. II (S) silencer and a lightened bolt, but this is ultimately not adopted. Instead, 50 guns are trialed with the E.S.6 (W.D.) silencer designed for the Sten Mk. V.

Sten Mk. VI

The final official Sten model is the Sten Mk. VI, essentially a Sten Mk .V equipped with an E.S.6 (W.D.) silencer, distinguished by a front sight akin to that on the Mk.II Sten. The Sten Mk. VI is first referenced in a January 1945 letter. The silencing unit, closely resembling the E.S.6 (W.D.) model for the Sten Mk. II but with minor differences and a removable barrel, is serially numbered to match the guns it is issued with. Although the Mk. V and VI models have the sear slightly repositioned to theoretically eliminate issues like double taps or runaway guns, these problems persisted. Winchester ammunition, which have more sensitive primers than those used in the Mk.IIz, causes the primer to ignite earlier, making the weapon function similarly to other Sten models.

A considerable number of Sten Mk. VI guns, potentially up to 25,000, are planned for manufacturing, but production halts at 14,300 due to the weapon’s unsatisfactory performance. About 80% of these are issued to the Special Operations Executive and 20% to the army. By June 1945, it is evident that the Mk. VI Sten is not successful, and most are never issued to troops. Attempts to rectify issues through adjustments to the bleed holes are unsuccessful. With the war ending, the British army decides to rely on existing stocks of Sten Mk. II (S) guns. The Sten Mk. VI is declared obsolete in January 1946, and most are initially slated for conversion back to Mk V configurations due to shortages, but this is ultimately deemed unnecessary due to the war’s conclusion and reluctance to initiate another extensive refurbishment project.