The Bofors 40 mm gun: A Swedish invention that defined World War II air defense

Wars & Conflicts · Published 15 October 2026 Swipe more like this →

In short: Designed in the 1930s to bridge the gap between small-caliber and heavy anti-aircraft weapons, the Bofors 40 mm L/60 became an iconic, widespread tool of war. Though technically obsolete by the jet age, its reliability and massive production numbers kept it in service long after the conflict ended.

The Bofors 40 mm L/60 originated from a 1928 contract between the Swedish Navy and AB Bofors, which sought a replacement for Vickers 2-pounder guns. The design process was complex, requiring a novel feeding mechanism to maintain a high rate of fire without the weight of traditional systems. By 1930, engineers perfected a design that ejected spent casings and reloaded by throwing fresh rounds into the breech. Production models, standardized as the 40 mm akan M/32, were officially designated L/60, though the actual barrel length was 56.25 calibers.

The weapon's effectiveness led to rapid international adoption. By 1939, it was in service with 18 countries, including the United Kingdom, which adapted the design for mass production. British engineers faced challenges with the original hand-assembled components, leading to modifications for industrial manufacturing. While the British initially experimented with the complex Kerrison Director for aiming, frontline units often relied on the simpler Stiffkey Sight or basic ring-and-post sights. The gun's versatility allowed it to be mounted on everything from naval cruisers to self-propelled tank chassis.

Beyond its primary role as an anti-aircraft weapon, the Bofors 40 mm L/60 proved surprisingly adaptable. During the North Africa campaign, British forces used the guns to fire tracer rounds, marking safe paths through minefields for advancing troops. The RAF Regiment utilized the weapon extensively for airfield defense, notably achieving the first ground-based shoot-down of a jet-powered Messerschmitt Me 262 in November 1944. Although superseded by the more powerful L/70 model in the post-war era, the sheer volume of surplus L/60 guns ensured their continued use in conflicts as late as the Yugoslav Wars.

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