5 years, 8 months and 5 days
the longest continuous military campaign of World War II
It was called the Battle of the Atlantic.
England required more than a million tons of goods each week for its people to survive and for the country to be able to fight its war against Germany.
Most of that tonnage came to England via the Northern Atlantic via merchant ships. Their vulnerability while crossing the Atlantic can not be over stated. German U-Boats and warships were always searching for them. If found, the goal was to sink the merchant ships and send the vitally needed supplies to the bottom of the ocean.
The problem, the Germans were quite good at their objective.
England faced a future were they could slowly starve to death and run out of the munitions needed to keep Hitler on his side of the English Chanel.
The loss of this vital lifeline, the outcome of the Battle of the Atlantic, was of great concern to Winston Churchill :
"Never for one moment could we forget that everything happening elsewhere, on land, at sea or in the air depended ultimately on its outcome."
— Winston Churchill
Combined Operations, responsible for command and control of the Battle of the Atlantic, was moved from Plymouth to Liverpool, Britain's main convoy port, in February of 1941. Over 1,000 convoys, averaging 3 or 4 each week, arrived in Liverpool during the war. Warships and Merchant ships were repaired and built, in Liverpool.
The Combined Operations complex, known locally as the "Citadel" or "Fortress", was designed to be bomb proof and gas proof, with a 7-foot thick roof and 3-foot thick walls, containing 100 rooms and covering an area of 50,000 square feet.
From this fortress the Royal Navy, Air Force and Royal Marines worked jointly there to monitor enemy warships, submarines and aircraft striving to bring England to her knees by choking off needed supplies.
From here, Britain worked to make sure that supplies and equipment needed by wartime Britain arrived where it was needed. Winning the Battle of the Atlantic was to the sea what the Battle of Britain was to the air. Superiority in both areas was vital in order for Britain to survive.
D-Day in June of 1944 would have been impossible if Germany had been the victor in the Battle of the Atlantic. The necessary troops and supplies could never have reached England. Allied victory may never have been achieved.
The Allies won the Battle of the Atlantic but the cost was high, on both sides:
3,500 Allied merchant ships, carrying 14.5 million tons of supplies , were sunk
175 Allied warships were sunk
72,200 Allied seaman lost their lives
783 German U-boats were sunk
30,000 German sailors, three quarters of the fleet, were killed
Such is the high price of victory.