Sten

The STEN (or Sten gun) is a family of British submachine guns chambered in 9×19mm and was used extensively by British and Commonwealth forces throughout World War II and the Korean War. They had a simple design and very low production cost, making them effective insurgency weapons for resistance groups, and they continue to see usage to this day by irregular military forces. The STEN served as the basis for the Sterling submachine gun, which replaced the STEN in British service until the 1980s, when it, and all other submachine guns, were replaced by the SA80.
The STEN is a select fire, blowback-operated weapon and loads its magazine on the left, rather than the bottom, as is the usual configuration.
STEN is an acronym, from the names of the weapon's chief designers, Major Reginald V. Shepherd and Harold Turpin, and EN for the Enfield factory.
Over four million Stens in various versions were made in the 1940s, making it the second most produced submachine gun of the Second World War, after the Soviet PPSh-41.
History.
The Sten emerged while Britain was engaged in the Battle of Britain, facing invasion by Germany. The army was forced to replace weapons lost during the evacuation from Dunkirk while expanding at the same time. Prior to 1941 (and even later) the British were purchasing all the Thompson submachine guns they could from the United States, but these did not meet demand, and Thompsons were much more expensive, costing anywhere from $70–200, whereas a Sten cost only $11. American entry into the war at the end of 1941 placed an even bigger demand on the facilities making Thompsons. In order to rapidly equip a sufficient fighting force to counter the Axis threat, the Royal Small Arms Factory, Enfield, was commissioned to produce an alternative.
The credited designers were Major R. V. Shepherd, OBE, Inspector of Armaments in the Ministry of Supply Design Department at The Royal Arsenal, Woolwich, (later Assistant Chief Superintendent at the Armaments Design Department) and Mr. Harold John Turpin, Senior Draughtsman of the Design Department of the Royal Small Arms Factory (RSAF), Enfield. Shepherd had been recalled to service after having retired and spending some time at the Birmingham Small Arms Company (BSA).
The Sten shared design features, such as its side-mounted magazine configuration, with the Royal Navy's Lanchester submachine gun, which was a copy of the German MP28. In terms of manufacture, the Lanchester was entirely different, being made of high-quality materials with pre-war fit and finish, in stark contrast to the Sten's austere execution. The Lanchester and Sten magazines were even interchangeable (though the Lanchester's magazine was longer with a 50-round capacity, compared to the Sten's 32.)
The Sten used simple stamped metal components and minor welding, which required minimal machining and manufacturing. Much of the production could be performed by small workshops, with the firearms assembled at the Enfield site. Over the period of manufacture, the Sten design was further simplified: the most basic model, the Mark III, could be produced from five man-hours of work. Some of the cheapest versions were made from only 47 different parts. The Mark I was a more finely finished weapon with a wooden foregrip and handle; later versions were generally more spartan, although the final version, the Mark V, which was produced after the threat of invasion had died down, was produced to a higher standard.
The Sten has been described by Max Hastings as: "highly unreliable, prone to jamming, and inaccurate beyond 30 metres. It was unsuitable for guerrilla operations in open country because it encouraged waste of ammunition. But it was easy and cheap to produce, a gun was said to cost fifteen shillings (three quarters of a pound), and was supplied to the (French) Resistance in huge quantities".
The Sten underwent various design improvements over the course of the war. For example, the Mark 4 cocking handle and corresponding hole drilled in the receiver were created to lock the bolt in the closed position to reduce the likelihood of unintentional discharges inherent in the design. Most changes to the production process were more subtle, designed to give greater ease of manufacture and increased reliability, and the potentially great differences in build quality contributed to the Sten's reputation as being an unreliable weapon. However, a 1940 report stated that "Exaggerated reports about the unreliability [of the Sten] were usually related to the quality of manufacture. Don Handscombe and his comrades in the Thundersley Patrol of the Auxiliary Units rated them more reliable than the Thompson SMG." Sten guns of late 1942 and beyond were highly effective weapons, though complaints of accidental discharge continued throughout the war.
The Sten was replaced by the Sterling submachine gun from 1953 and was gradually withdrawn from British service in the 1960s. Other Commonwealth nations followed suit, either by creating their own replacements, such as the Australian F1 submachine gun, or adopting foreign designs.
Design.
The Sten was a blowback-operated submachine gun firing from an open bolt with a fixed firing pin on the face of the bolt. This means the bolt remains to the rear when the weapon is cocked, and on pulling the trigger the bolt moves forward from spring pressure, stripping the round from the magazine, chambering it and firing the weapon all in the same movement. There is no breech locking mechanism, the rearward movement of the bolt caused by the recoil impulse is arrested only by the mainspring and the bolt's inertia. The German MP40, Russian PPSh-41, and US M3 submachine gun, among others, used the same operating mechanisms and design philosophy of the Sten, namely their low cost and ease of manufacture. Though the MP40 was also built largely for this purpose, Otto Skorzeny went on record saying that he preferred the Sten because it required less raw materials to produce, and performed better under adverse combat conditions. The effect of putting lightweight automatic weaponry into the hands of soldiers, greatly increased the short-range firepower of the infantry, especially when the main infantry weapon was a bolt-action rifle capable of only around 15 rounds per minute and not suited for short-range combat. However, the open-bolt firing mechanism, short barrel, and use of pistol ammunition severely restricted accuracy and stopping power, with an effective range of only around , compared to for the Lee–Enfield rifle.
Stoppages could occur for a variety of reasons: some as a result of poor maintenance, while others were particular to the Sten. Carbon buildup on the face of the breech or debris in the bolt raceway could cause a failure to fire, while a dirty chamber could cause a failure to feed. Firing the Sten by grasping the magazine with the supporting hand tended to wear the magazine catch, altering the angle of feed and causing a failure to feed: the correct method of holding the weapon was as with a rifle, the left hand cradling the fore piece.
Additional problems stemmed from the Sten's magazine, which was a direct copy of the one used in the German MP40, originally in order to facilitate the use of that weapon's magazines. Unfortunately, this decision meant incorporating that magazine's faults in the process. The magazine had two columns of 9 mm cartridges in a staggered arrangement, merging at the top to form a single column. While other staggered magazines, such as the Thompson, fed from both the left and right side alternately (known as "double-column, staggered-feed"), the Sten magazine, like the MP40, required the cartridges to gradually merge at the top of the magazine to form a single column ("double column, single feed"). As a consequence, any dirt or foreign matter in this taper area could cause feed malfunctions. Additionally, the walls of the magazine lip had to endure the full stresses of the rounds being pushed in by the spring. This, along with rough handling could result in deformation of the magazine lips (which required a precise 8° feed angle to operate), resulting in misfeeding and a failure to fire. Modern 9 mm magazines, such as those used by the Sterling submachine gun, are curved and feed both sides to avoid this problem. If a Sten failed to feed due to jammed cartridges in the magazine, standard practice to clear it was as follows: remove magazine from Sten, tap the base of the magazine against the knee, re-insert magazine in Sten, then recocking the weapon and firing again as normal. To facilitate easier loading when attempting to push the cartridges down to insert the next one, a magazine filler tool was developed and formed part of the weapon's kit.
The slot on the side of the body where the cocking knob ran was also a target of criticism, as the long opening could allow foreign objects to enter. On the other hand, a beneficial side-effect of the Sten's minimalist design was that it would fire without any lubrication. This proved useful in desert environments such as the Western Desert Campaign, where lubricating oil retained dust and sand.
The open bolt design combined with cheap manufacture and rudimentary safety devices also meant the weapon was prone to accidental discharges, which proved hazardous. A simple safety could be engaged while the bolt was in the rearwards (cocked) position. However, if a loaded Sten with the bolt in the closed position was dropped, or the butt was knocked against the ground, the bolt could move far enough rearward to pick up a round (but not far enough to be engaged by the trigger mechanism) and the spring pressure could be enough to chamber and fire the round. The Mk. IV's cocking handle was designed to prevent this by enabling the bolt to be locked in its forward position, thereby immobilising it. Wear and manufacturing tolerances could render these safety devices ineffective.
Though the Sten was somewhat prone to malfunction, in the hands of a well-disciplined soldier, who knew what these issues were, and how to avoid them, they were less of a liability as otherwise may be suggested. According to Leroy Thompson, "Troops usually made the conscious choice to keep the Sten with a magazine in place, based on the assumption that they might need it quickly. It might, then, be argued that more troops were saved by having their Sten ready when an enemy was suddenly encountered than were injured by accident. The Sten was more dangerous to its users than most infantry weapons, but all weapons are dangerous."
Variants.
Sten guns were produced in several basic marks (though the Mk I saw limited service, and the Mk IV was never issued), and nearly half of the total produced were Mark II versions. Approximately 4.5 million Stens in all their variants were produced during the Second World War.
Mark I.
The first ever Mk I Sten gun (number 'T-40/1' indicating its originator Harold Turpin, the year 1940 and the serial number "1") was handmade by Turpin at the Philco Radio works at Perivale, Middlesex during December 1940/January 1941. This particular weapon is held by the historical weapons collection of the British Army's Infantry and Small Arms School Corps in Warminster, Wiltshire.
The first model had a conical flash hider and fine finish. It had a wooden foregrip and forward handle (sometimes this was made of steel), as well for a section of the stock. The stock was a small tube outline, rather like the Mark II Canadian. One unique feature was that the front pistol grip could be rotated forward to make it easier to stow. The barrel sleeve extended all the way to the end, where it met the flash hider. Along the top of the tube surrounding the barrel was a line of small holes and its sights were configured somewhat differently. About 100,000 were made before production switched to the Mark II. Sten Mk I's in German possession were designated MP 748(e), the 'e' standing for "englisch".
Mark I*.
This was the first simplification of the Mk I. The foregrip, the wooden furniture and the flash hider were removed for production expediency.
Mark II.
The Mark II was the most common variant, with two million units produced. It was a much rougher weapon than the Mk I. The flash eliminator and the folding handle (the grip) of the Mk I were omitted. A removable barrel was now provided which projected beyond the barrel sleeve. Also, a special catch allowed the magazine to be slid partly out of the magazine housing and the housing rotated 90 degrees counter-clockwise (from the operator's perspective), together covering the ejection opening and allowing the weapon and magazine both to lie flat on its side. 
The barrel sleeve was shorter and rather than having small holes on the top, it had three sets of three holes equally spaced on the shroud. To allow a soldier to hold a Sten by the hot barrel sleeve with the supporting hand, an insulating lace-on leather sleeve guard was sometimes issued.< Sten Mk II's in German possession were designated MP 749(e), the "e" signifying "englisch". Some Mk IIs were fitted with a wooden stock as this part was desirable and interchangeable with the Mk V. The Spz-kr assault rifle, a rudimentary German design made in the closing stages of the war, used the receiver and components from the Sten Mk II, and the MP 3008 was made as a cheap copy.
Mark II (Canadian).
During World War II a version of the Sten gun was produced at the Long Branch Arsenal in Long Branch, Ontario (now part of Toronto, Ontario). This was very similar to the regular Mark II, with a different stock ('skeleton' type instead of strut type) and improved quality of manufacture. It was first used in combat in the Dieppe Raid in 1942.
The Mark II is made in China with a copy known as the M38. The Chinese M38s were made in an automatic-only configuration, unlike the standard Mark II. The M38 was made in 9x19mm and 7.62×25mm Tokarev variants.
Mark III.
This simple design was the next most commonly produced after the Mark II. A result of the manufacturer Lines Bros Ltd stating it could build a modified design that was quicker and cheaper to build than the Mk II, it was a simplification of the Mk I made both in Canada and the UK, and Lines Bros Ltd was the largest manufacturer. The Mark III was made of 48 parts, compared to the Mark II's 69, but the Mark II remained more commonplace for logistical reasons - parts between the two were not interchangeable. Though slightly lighter, the magazine well was fixed in place, and the barrel could not be removed, meaning if it was damaged the weapon had to be scrapped. Combined with the fact the Mark III was more prone to failure than the Mark II, production of the weapon ceased in September 1943. The biggest difference from the Mark II was the unification of the receiver, ejection port, and barrel shroud that now extended farther up the barrel. The barrel was fixed and the body was welded shut along the centre of the top. Captured Sten Mk III's in German possession were designated MP 750(e). A total of 876,886 Mark III's were produced.
Mark V.
Introduced in 1944, the Mk V was a better-quality, more elaborate version of the Mk II. Changes included a wooden pistol grip, a vertical wooden foregrip, a wooden stock, and a bayonet mount. There was a No. 4 Lee–Enfield rear sight and the weapon was of better quality manufacture and finish than the Mk II and Mk III.
Another variant of the Mk V had a swivel stock and rear sight mirror intended for firing around corners in urban warfare, similar to the Krummlauf developed by the Germans for the StG 44.
Suppressed models.
Mk IIS and Mk VI models incorporated an integral suppressor and had a lower muzzle velocity than the others due to a ported barrel intended to reduce velocity to below the speed of sound; . The suppressor heated up rapidly when the weapon was fired, and a canvas cover was laced around the suppressor for protection for the firer's supporting hand.
The suppressed models were produced at the request of the Special Operations Executive (SOE) for use in clandestine operations in occupied Europe, starting with the Mk IIS in 1943. Owing to their tendency to overheat, they were fired in short bursts or single shots.
In addition to its use in the European Theatre, the Mk IIS saw service with clandestine units in the Southwest Pacific Area (SWPA) such as the Services Reconnaissance Department and SOE's Force 136 on operations against the Imperial Japanese Army. The Sten Mk IIS was used by the Operation Jaywick party during their raid into Japanese-occupied Singapore Harbour.
The Sten Mk IIS also saw service with the Special Air Service Regiment during the Vietnam War.
Service.
The Sten, especially the Mark II, tended to attract affection and loathing in equal measure. Its peculiar appearance when compared to other firearms of the era, combined with sometimes questionable reliability made it unpopular with some front-line troops. It gained nicknames such as "Plumber's Nightmare", "Plumber's Abortion", or "Stench Gun". The Sten's advantage was its ease of mass-production manufacture in a time of shortage during a major conflict.
Made by a variety of manufacturers, often with subcontracted parts, some early Sten guns were made poorly and/or not made to specification, and could malfunction in operation, sometimes in combat. The double-column, single-feed magazine copied from the German MP28 was never completely satisfactory, and hasty manufacturing processes often exacerbated misfeed problems inherent in the design. A common statement heard from British forces at the time was that the Sten was made "by Marks and Spencer out of Woolworth." British and Commonwealth forces in the early years of the war often extensively test-fired their weapons in training to weed out bad examples; a last-minute issue of newly manufactured Stens prior to going into action was not always welcomed.
The MK II and MK III Stens were regarded by many soldiers as very temperamental, and could accidentally discharge if dropped or even laid on the ground whilst the gun was cocked. Others would fire full-automatic when placed on 'single', or fire single shots when placed on 'automatic'. This was particularly true of early Stens using bronze bolts, where the sear projection underneath the bolt could wear down more easily than ones made of case-hardened steel.
Stens could jam at inopportune moments. One of the more notable instances of this was the assassination of SS-Obergruppenführer Reinhard Heydrich on 27 May 1942, when a Czechoslovak soldier—Warrant Officer Jozef Gabčík—wanted to fire his Sten point blank at Heydrich, only to have it misfire. His comrade Jan Kubiš then hastily tossed a grenade, which mortally wounded Heydrich. There are other accounts of the Sten's unreliability, some of them true, some exaggerated and some which are apocryphal. France manufactured (well-made) Sten copies postwar into the early 1950s, evidently believing in the basic reliability and durability of the design.
A well-maintained (and properly functioning) Sten gun was a devastating close-range weapon for sections previously armed only with bolt-action rifles. In addition to regular British and Commonwealth military service, Stens were air-dropped in quantity to resistance fighters and partisans throughout occupied Europe. Due to their slim profile and ease of disassembly/reassembly, they were good for concealment and guerrilla warfare. Wrapping the barrel in wet rags would delay undesirable overheating of the barrel. Guerrilla fighters in Europe became adept at repairing, modifying and eventually scratch-building clones of the Sten (over 2,000 Stens and about 500 of the similar Błyskawica SMGs were manufactured in occupied Poland).
Canadian infantry battalions in northwest Europe retained spare Sten guns for special missions and the Canadian Army reported a surplus of the weapons in 1944.
The Sten saw use even after the economic crunch of World War II, replacing the Royal Navy's Lanchester submachine guns into the 1960s, and was used in the Korean War, including specialist versions for British Commandos. It was slowly withdrawn from British Army service in the 1960s and replaced by the Sterling SMG; Canada also phased out the Sten, replacing it with the C1 SMG.
The Sten was one of the few weapons that the State of Israel could produce domestically during the 1948 Arab–Israeli War. Even before the declaration of the State of Israel, the Yishuv had been producing Stens for the Haganah; after the declaration, Israel continued making Stens for IDF use. The opposing side also used (mostly British-made) Stens, particularly the irregular and semi-regular Arab Liberation Army.
In the 1950s "L numbering" came into use in the British Army for weapons—Stens were then known as L50 (Mk II), L51 (Mk III) and L52 (Mk V).
One of the last times the Sten was used in combat during British service was with the RUC during the IRA border campaign of 1956–1962. In foreign service, the Sten was used in combat at least as recently as the Indo-Pakistani War of 1971.
In 1971 various marks of Stens were used by guerilla fighters during the Bangladesh Liberation War.
A number of suppressed Stens were in limited use by the US Special Forces during the Vietnam war, including c. 1971, by the United States Army Rangers.
In 1984, Indian prime minister Indira Gandhi was assassinated by two of her bodyguards, one of whom fired the entire magazine (30 rounds) of his Sten at point-blank range, of which 27 hit her.
In the Second Sino-Japanese War and the Chinese Civil War, both nationalists and communists used the Sten. Some Stens were converted by the communists to 7.62×25mm by using the magazine housing from a PPS to accept curved PPS magazines. British, Canadian, and Chinese Stens were seen in the hands of the communists during the Korean and Vietnam Wars.
The Finnish Army acquired moderate numbers of Stens in the late 1950s, mainly Mk. III versions. Refurbishment at the Kuopio Arsenal included bluing of the arms. Stens in Finnish service saw limited usage by conscripts (notably combat swimmers) and were mostly stockpiled for use in a future mobilization.
During the Zapatista movement in 1994 some Zapatista soldiers were armed with Sten guns.