Within hours of the outbreak of the Second World War, Winston Churchill took up office as First Lord of the Admiralty. The same day the liner Athenia was torpedoed in the Atlantic in the first U-boat attack of the war. Churchill quickly recognised Britain’s survival depended on countering the U-boat threat and the strategic importance of protecting Allied merchant shipping with measures such as the convoy system.

As this superbly researched book reveals, the Nazi U-boat fleet was relatively small and unprepared for war in 1939. But by early 1941 its numbers and effectiveness had increasing to the point that Hitler was able to declare ‘our warfare at sea is just beginning’. Prime Minister Churchill’s response was to issue his famous ‘Battle of the Atlantic’ Directive.

Churchill’s Atlantic Convoys describes the political, strategic and tactical ebb and flow of events, particularly between 1942 and 1943. Thanks to increased numbers and scientific innovations the Allies slowly gained the upper hand despite a determined German fight back in late 1943 and early 1944. While the U-boat threat was never wholly defeated, the tenacity and sacrifices of the Allied naval forces won the day.

Churchill later recognised the persistence of Germany’s effort and the fortitude of the U-boat service. It would not be until 7 June 1945 that Churchill and President Truman felt able to assert ‘the Allies have finished the job’.