High Quality Content by WIKIPEDIA articles! The Bofors 40 mm gun is an anti-aircraft autocannon designed by the Swedish defence firm of Bofors Defence (the company was acquired in September 2000 by United Defense Industries but is now a part of BAE Systems AB since March 2005). It was one of the most popular medium-weight anti-aircraft systems during World War II, used by most of the western Allies as well as by the Axis powers. The cannon remains in service as of 2011, making it one of the longest-serving artillery pieces of all time. It is often referred to simply as the Bofors gun.