The STEN (or Sten gun) is a family of British submachine guns chambered in 9×19mm which were 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 1990s, when it, and all other submachine guns, were replaced by the SA80.
The Sten is a select fire, blowback-operated weapon which mounts its magazine on the left. Sten is an acronym, from the names of the weapon's chief designers, Major Reginald V. Shepherd and Harold J. Turpin, and "En" for the Enfield factory.[9] 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.
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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. After the start of the war and to 1941 (and even later), the British purchased all the Thompson submachine guns they could from the United States, but these did not meet demand, and Thompsons were expensive, the M1928 costing $200 in 1939 (and still $70 in 1942), whereas a Sten would turn out to cost only $11.[12] 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.
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The Sten shared design features, such as its side-mounted magazine configuration, with the Lanchester submachine gun being produced at the same time for the Royal Navy and Royal Air Force, 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.)[13]
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.[14] 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 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."[15] Sten guns of late 1942 and beyond were highly effective weapons, though complaints of accidental discharge continued throughout the war.
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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 material to produce and performed better under adverse combat conditions.[16] 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.[citation needed] 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 100 m (330 ft), compared to 500 m (1,600 ft) for the Lee–Enfield rifle.
Stoppages could occur for poor maintenance, while others were particular to the Sten. Carbon build up 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.[17] Firing the Sten by grasping the magazine with the supporting hand, contrary to instruction, 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.
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On the other hand, a beneficial side-effect of the Sten's minimalist design was that it would fire without any lubrication.[17] This proved useful in desert environments such as the Western Desert campaign, where lubricating oil retained dust and sand.
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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, 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-trained soldier, who knew how to avoid the Sten's failings, 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".[16]
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Rate of fire version dependent; ~500–600 round/min
Muzzle velocity 365 m/s (1,198 ft/s) 305 m/s (1,001 ft/s) (suppressed models)
