The Strategic Decision Behind the 9mm Rounds in WWII British STEN Submachine Guns

During World War II, the British military made a strategic decision to equip the STEN (Super Tyne Experimental Nigel) submachine guns with 9mm rounds. This choice was influenced by a variety of tactical and logistical factors that, to the scrutiny of many, appeared curious at the time. In this article, we will explore the reasoning behind this decision and contrast it with the British .455 Webley handgun cartridges, which were also available during the war.

Cost-Effectiveness and Guerrilla Warfare

One of the key reasons for choosing the 9mm round was its economical production process. 9mm cartridges, produced at a cost of approximately 10 shillings each, were essential for their utility not just on the main battlefields but also in the support efforts of resistance movements in Europe. For instances where large-scale air drops were not feasible or timely, 9mm rounds enabled guerrilla fighters to quickly procure and utilize ammunition from German stockpiles or secure it locally.

In contrast, the British .455 Webley round was primarily reserved for rear-echelon personnel, such as administrative staff and support units. The 9mm round was better suited for the skirmishes and urban combat environments faced by STEN users, such as the resistance fighters and select military units. Moreover, the ability to acquire additional 9mm ammunition from captured German stocks provided a more sustainable and readily available source of supply.

Logistical and Tactical Considerations

The .455 Webley round was indeed a secondary revolver cartridge, used mainly by non-combatants and support staff. While it offered a certain level of stopping power, it was not the preferred choice for close-quarters combat, which was the primary application for STEN submachine guns. The .38-200 cartridge, used by the BHP revolver, was similarly suited for rear-line personnel and did not offer the same utility for close combat.

The 9mm round used in the STEN was specifically designed for high-capacity, manual recoil-operated guns, offering a balance between firepower and mobility. A lesser-known fact is that the BHP revolver and the stricter .455 Webley round from the British Webley revolvers were not considered for widespread adoption due to their historical context and age. While the .455 was an effective cartridge, it was anachronistic and not well-suited for modern combat scenarios.

Furthermore, the British Army had already settled on 9mm as a standard issue round by the time the STEN was developed in 1941. This decision was influenced by the broader need for a reliable and compact round that could be effectively used in a variety of roles, from the front lines to support duties. The Browning Hi-Power was imported and produced in Canada, and designs like this demonstrated the British military's confidence in the 9mm round as a future standard.

The Non-Use of .303 and 7.62mm Rounds

A frequent inquiry posits that the STEN should have utilized the standard British .303 round, like the Bren Light Machine Gun (LMG). However, this decision was influenced by the specific needs of the STEN in close combat scenarios. The shorter length of the 9mm cartridge made it more suitable for the compact size and rapid-fire requirements of a submachine gun.

While it is true that the standard .303 round would have offered more stopping power, the design features required to handle such a round would have significantly increased the weight and complexity of the STEN, which was already optimized for quick and efficient use. The .303 round, with its higher barrel velocity, would indeed have provided more effective terminal ballistics, but the balance of weight, ease of carriage, and operational simplicity made the 9mm round the superior choice for rapid-fire, high-velocity engagements.

Conclusion

The use of 9mm rounds in the British STEN submachine gun was a calculated strategic decision designed to optimize performance in a multitude of tactical scenarios. It was a pragmatic compromise between cost-effectiveness, ease of supply, and operational efficiency. While the British .455 Webley and .303 rounds served important roles, they were not suitable for the specific requirements of the STEN in its intended applications. This decision ultimately contributed to the widespread adoption and significant impact of the STEN in both official British military units and resistance movements across Europe.

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