On June 15, 1944, 297 planes (155 Avro Lancasters, 130 Handley Page Halifaxes, and 12 De Havilland Mosquitos) of the Royal Air Force bombed Boulogne harbour to suppress German naval activity following D-Day. Some of the Lancasters carried Tallboy bombs. As a result, the harbour and the surrounding area were completely destroyed. In August, 1944 the town had been declared a "fortress" by Adolf Hitler, but it succumbed to assault and liberation by the 3rd Canadian Division in September. In one incident, a French civilian guided the Canadians to a "secret passage" leading into the walled old town and by-passing the German defenders.