Sten is an acronym, derived from the names of the weapon's chief designers: Major Reginald V. Shepherd and Harold J. Turpin, and "En" for the Enfield factory.

[12][b] Around 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.

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.

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.

)[16] The Sten used simple stamped metal components and minor welding, which required minimal machining and manufacturing.

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.

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.

Historian John Warwicker claimed "Exaggerated reports about the unreliability [of the Sten] were usually related to the quality of manufacture.

"[19] Sten guns of late 1942 and beyond were highly effective weapons, though complaints of accidental discharge continued throughout the war.

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.

[21] 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.

[21] 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.

The open bolt design combined with cheap manufacture and rudimentary safety devices also meant the weapon was prone to accidental discharges, which proved hazardous.

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.

The magazine insert was fixed to the receiver with screws (unlike the later found on Mark II+ variants that could be rotated 90 degrees for stowage).

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.

Its peculiar appearance when compared to other firearms of the era, combined with sometimes questionable reliability made it unpopular with some front-line troops.

[55] The double-column, single-feed magazine copied from the German MP28 was never completely satisfactory, and hasty manufacturing processes often exacerbated the 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.

"[56] 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 welcomed.

[citation needed] The MK II and 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.

France[57] 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.

[61] 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.

[62] 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.

Stens in Finnish service saw limited usage by conscripts (notably combat swimmers) and were mostly stockpiled for use in a future mobilization.