What happened at the battle of the Atlantic?

The Battle of the Atlantic was a see saw maritime action which began in 1939 with the commencement of hostilities and only ended with the defeat of Germany in May 1945. The allied goals were to blockade Germany by sea; to defeat the U-boat menace; and to keep open the supply lines between the U.S. , Britain, and the U.S.S.R. The German goal was to destroy allied shipping. The battle was a strategic victory for the allies. The cost was heavy on both sides: 3,500 allied merchant ships and 783 German submarines were sunk.