4. Battle of the Atlantic, 1939-45

SUMMARY

Winston Churchill once wrote that, '... the only thing that ever really frightened me during the war was the U-boat peril'. In saying this, he correctly identified the importance of the threat posed during World War Two by German submarines (the 'Unterseeboot') to the Atlantic lifeline. This lifeline was Britain's 'centre of gravity' - the loss of which would probably have led to wholesale defeat in the war.

Germany's best hope of defeating Britain lay in winning the Battle of the Atlantic.  If Germany had prevented merchant ships from carrying food, raw materials, troops and their equipment from North America to Britain, the outcome of World War II could have been radically different.  Britain might have been starved into submission, and her armies would not have been equipped with American-built tanks and vehicles.  Moreover, if the Allies had not been able to move ships about the North Atlantic, it would have been impossible to project British and American land forces ashore in the Mediterranean theatres or on D-Day. Germany's best hope of defeating Britain lay in winning what Churchill christened the 'Battle of the Atlantic'.

In order to be effective hunters of merchant vessels, U-boat crews could be away from port for many weeks at a time.  The submarines would travel, much like a small boat across known shipping lanes, looking and waiting for an Allied merchant vessel to come over the horizon.  If the merchant ship was armed or had escorts, the U-boat would then submerge underwater and bring down the ship with explosive torpedoes—one shot could break a ship apart and sink it in a matter of minutes.  If the merchant was alone and unarmed, the U-boat would open fire with its deck guns to sink the Allied vessel.

U-boats, supplemented by mines, aircraft and surface ships, succeeded in sinking three million tons of Allied shipping between the fall of France in June 1940 and the end of the year. Admiral Dönitz, the commander of the U-boat arm, introduced the 'wolfpack' tactic at the end of 1940, whereby a group of submarines would surface and attack at night, thus greatly reducing the effectiveness of sonar. 

Not surprisingly, the German submariners called this phase of the war the 'happy time'. This remorseless attrition of merchant shipping was a far greater threat to Britain's survival than the remote possibility of the Kriegsmarine landing German troops on the English coast.  Churchill’s fear of the U-boats choking off the island nation’s supply chain was close to becoming a reality as the British were losing more ships than they were producing.

However, several factors contributed to a major turnaround in the Battle of the Atlantic.  The Allied forces created new tactics to combat the U-boat threat.  The British introduced small armed escorts to guard over a large number of merchant ships called a convoy.  Additionally, Allied sailors used a new underwater sound detection system, ASDIC (or sonar) to find submarines and could destroy them with weapons such as deck guns, depth charge, heavy explosive devices called “hedgehogs” and aircraft.  Perhaps the most important factor was the entry of America into the war.  The vast power of American industry increased the flow of supplies to Britain that far outweighed the effectiveness of the U-Boats.  In fact, American ship factories could produce an entire merchant vessel in a mere 48 hours!  

By 1944, the effectiveness of the U-boats were so far diminished that Britain’s supply line was never again endangered.  In fact, Britain went from being a nation on the brink of a logistics disaster to the launching point of the greatest amphibious invasion in history.