40mm Bofors

Originally designed by Bofors under contract from the Swedish Navy in the 1930s, the first Commonwealth use was in 1937 when the British Army acquired license to modify and mass produce the design. This Light Anti-Aircraft gun was used in Canadian service from 1941-1959, replacing obsolete guns remaining after WWI. 

British, Canadian, and Australian factories produced over 2,100 of these guns over the course of WWII as they became the standard light anti-aircraft weapon for multiple types of warships from minesweepers to battleships.

Bofors were versatile and varied significantly in design from country to country, with some models being air-cooled while others were water-cooled to allow for longer firing bursts against aircraft. Multiple types of ammunition were also used, especially after WWII. They remain in use to this day.

Several guns were removed from HMCS Bonaventure and put back into artillery service to defend Canadian airfields in Germany from 1970-1987. In August 1990, HMCS Protecteur, a supply ship deployed in the Gulf, received two guns, also originally from Bonaventure

Reference Links:
The Royal Canadian Artillery Museum - Bofors Light Anti-Aircraft Gun
Canadian War Museum - Bofors 40mm Anit-Aircraft Gun