This six-year struggle to secure the Atlantic supply routes was essential to the survival of the United Kingdom and the Allied cause. Canadians played a critical role in the longest and perhaps most important battle of the Second World War, whether in the services, the Merchant Navy or the nation's shipyards. Operating in submarine-infested and unforgiving waters, the Royal Canadian Navy grew from a handful of ships to become the third largest in the world. Without the sacrifice of those who braved the perilous ocean crossings there would have been no Allied victory in Europe in 1945.