"During the war only one thing ever frightened me - the U-Boat peril. Battles might be won or lost but our power to fight and keep ourselves alive rested on our struggle to keep control of the Atlantic."  - Sir Winston Churchill

The Battle of the Atlantic was the longest and most important campaign of the Second World War. For almost six years German U-boats and Canadian, British and American warships fought a brutal war for control of the Atlantic's shipping lanes. At stake, the very existence of Great Britain and the future of the Allied war effort. If the convoys sailing from America and Canada failed to arrive in British ports the war would have been lost.

Both the Nazis and the British knew that whatever other battles were fought, the most decisive would be fought at sea, in the shipping lanes of the North Atlantic. The mostly unarmed merchant ships were escorted in convoys of between 30 and 70 ships, protected by the Royal Navy and Royal Canadian Navy. Beneath the waves, however, lurked a silent, deadly threat - the U-Boat. Although the Germans start the battle with a small number of operation subs, by the climax of the war, hundreds prowled the Atlantic in search of merchant ships.

Thus the scene was set for one of the largest and deadliest naval wars in history. The Battle of the Atlantic would claim more than 4,500 vessels and close to 100,000 lives. Britain's losses brought the Allies to the brink of defeat. But rescue came from across the Atlantic - from her Canadian allies, from the Commonwealth and later from America.

Using a powerful mix of recreation, eyewitness testimony and computer animation, this four part series examines the key events of the war (from outbreak to D-Day) and explores the lives of the Allied sailors and German submariners who fought above and beneath the surface of the stormy Atlantic. The series also investigates the impact that new technologies had on the cat and mouse game that is submarine warfare. 

This is the Battle of the Atlantic, in the words of the men who fought it.