40mm Bofors Round from a WWII M25

The Bofors 40 mm Automatic Gun L/60 (often referred to simply as the "Bofors 40 mm gun", the “Bofors gun”) is an anti-aircraft autocannon, designed in the 1930s by the Swedish arms manufacturer AB Bofors. The gun was designed as an intermediate anti-aircraft gun, filling the gap between fast firing close-range small calibre anti-aircraft guns and slower firing long-range high calibre anti-aircraft guns. For its time, the Bofors 40 mm L/60 was perfectly suited for this role and outperformed competing designs in the years leading up to World War II in both effectiveness and reliability.

It entered the export market around 1932,and was in service with 18 countries by 1939.  Throughout World War II it became one of the most popular and widespread medium-weight anti-aircraft guns. It was used by the majority of the western Allies and some Axis powers such as Nazi Germany and Hungary.

In the post-war era, the Bofors 40 mm L/60 design was not suitable for action against jet-powered aircraft, so Bofors developed a new 40 mm replacement design with significantly more power—the Bofors 40 mm Automatic Gun L/70