The Bofors 40mm gun served in every Alllied army in World War II, even the Germans. Both the British and the Americans built this Swedish design in huge numbers. The Allies had superior anti-aircraft artillery firepower with this rapid-fire weapon. Many American sailors remember this weapon well. Dover Castle had many gun emplacements during World War II on her upper battlements for 40mm Bofors, but this is the only one left. Right-click and choose "view image" to enlarge.
This is the ground-based version of the 40mm Bofors gun on HMS Belfast.