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The Bofors 40 mm gun is the short name applied to either of three similar automatic cannon designs by Swedish arms manufacturer AB Bofors and which fire a 40 mm projectile. These designs were primarily intended to be employed in the anti-aircraft role. The initial design was the Bofors 40 mm L/43 model 1932 which saw limited naval use. The Bofors 40 mm Automatic Gun L/60 is the most prolific of the three designs, seeing service with both Allied and Axis forces during World War II in both naval and field applications. In American use it was known as the Bofors 40 mm L/56 though there is no actual design difference. The Bofors 40 mm Automatic Gun L/70 model 1948 was of a similar basic design to the L/60 but chambered for a larger, more powerful cartridge. The two main designs have been give numerous designations depending upon their country of service and mounting.

The guns employ a falling breechblock. The mechanism for the firing cycle (ejection and rechambering a new round) is powered by the recoil from firing.

Both the L/60 and L/70 designs have had enduring service lives. Consequently, the generic description of "Bofors 40 mm gun" is insufficient to distinguish the two models without further information.

Bofors 40 mm Automatic Gun L/43
The Bofors 40 mm Automatic Gun L/43 model 1932 was the earliest design of 40 mm autocannon produced by Bofors for the Swedish Navy. It was adopted as a submarine anti-aircraft weapon, where the mount was retracted into a waterproof cylinder. It used the same 40×311mmR cartridge as the later L/60 but with a lower propellant charge.

Bofors 40 mm Automatic Gun L/60


The Bofors 40 mm Automatic Gun L/60 was a medium weight anti-aircraft gun that was first released as the model 1934 and then, with only slight modification, as the model 1936. It was the model 1936 that was used for most guns produced during World War II. By 1939, it was in service with 18 different countries. It was used by the majority of the western Allies and some Axis powers such as Nazi Germany and Hungary.

The L/60 was produced as a single barrel gun and as a dual gun. The dual gun consisted of a left and right version, mounted side by side and joined in manufacture as a single unit. For field employment, it was extensively produced as a towed gun, though it was also mounted to truck and tank chassis. In naval service, it was produced on single, twin and quad mounts, with the quad mounts consisting of two dual guns. Designed as an air-cooled gun, water cooled guns were also produced to improve sustained fire.

With the emergence of jet aircraft, the L/60 would become obsolete as an anti-aircraft weapon, but would continue in naval service as the main armament of many small vessels past the turn of the century (2000). The Bofors L/60s have been used in the United States Air Force's Lockheed AC-130 gunships in the air-to-ground role.

Various "marks" of the gun refer to variation in mount, configuration and sighting rather than a fundamental modification of the actual gun.

US manufactured L/56 guns


The "L" designation represents the barrel length as multiples of the bore diameter. The "nominal length" of the L/60 barrel is 2400 mm. The actual length of the L/60 barrel is 56.25 calibres (2250 mm). Consequently, in US service, the gun was designated as L/56. There is no actual difference in barrel length.

The L/56 was manufactured in the US by the Chrysler Corporation under licence. Drawings provided by Bofors were not only converted from metric to imperial units, but they were also toleranced to facilitate mass production. The original design specifications frequently called for hand finishing of components to "fit", which was incompatible with mass production. Consequently, components of US manufactured guns are largely incompatible with those manufacture to Bofors' specifications.

Bofors 40 mm Automatic Gun L/70
The Bofors 40 mm Automatic Gun L/70 model 1948 was of a similar basic design to the L/60 but chambered for a larger, more powerful 40 × 365 mm R cartridge. Proximity fuzed ammunition, introduced in the 1970s, increased the effectiveness of the gun in the anti-aircraft role. While the L/70 has never been as prolific as the L/60, it has nonetheless had a similarly enduring service life and been adopted by over 40 different nations.

It has been produced with mountings for both field and naval employment. While largely superseded by missiles in the short-range anti-aircraft role, a variant of the L/70 is the basis of the DARDO close-in weapon system (CIWS) produced by Oto Melara (formerly Breda). The design has also been adapted for use as the main armament in light armoured vehicles.