By the middle of the war, as Crusaders were being replaced by M4 Shermans, the British converted some by fitting 40mm Bofors (Mk I) and later twin 20mm Oerlikon anti aircraft guns (Mk II and Mk III). These AA tanks saw service, albeit limited because of Allied air superiority, during the NW European campaign of 1944-1945 coming ashore via the Mulberry harbour at Aromanches in Normandy.