During the Second World War the Royal Canadian Navy and the Royal Canadian Air Force protected shipping on vital North Atlantic routes which were the lifeline of the Allies. Army units shared in the defence of the seaports which were essential to that shipping. In the face of a determined campaign by German submarines and despite heavy losses, the Atlantic routes were kept open. Canada's most heavily defended port, Halifax served as the main convoy assembly point for outbound traffic and played a key role in furthering the delivery of desperately needed wartime materiel.