The Battle of the Atlantic, the longest single engagement of the Second World War, resulted in the coming-of-age of the Royal Canadian Navy. By 1945, the Canadian Navy had transformed from a small force of 3,500 personnel and 13 vessels into the third-largest naval power in the world. As German U-boats threatened to weaken the Allied war effort, the Canadian Navy was put to work protecting convoys across the Atlantic and hunting for submarines off the coast of Atlantic Canada.

War at Sea uses first-hand accounts from the veterans who survived, as well as a detailed catalogue of the technology, weapons, and ships, to describe the history of this pivotal conflict. Author Ken Smith emphasizes the contribution of Atlantic Canadians, who worked in areas vital to the war effort while under constant threat from U-boats, sabotage, and spies.