Karl Dönitz was the German naval commander who masterminded the U-boat campaign against Allied shipping in the Second World War and who, in the war's final days, briefly succeeded Adolf Hitler as head of the Third Reich. Born in Prussia, he joined the Imperial German Navy before the First World War and served in submarines, an experience that shaped the rest of his career.
Between the wars he became the foremost advocate of submarine warfare, and when the Second World War began he commanded Germany's U-boat fleet. He developed the deadly "wolf pack" tactics, in which groups of submarines attacked Allied convoys in coordinated assaults, and for a time the U-boats came perilously close to severing the Atlantic lifeline between North America and Britain.
As the Allies developed better escorts, radar, code-breaking, and air cover, the tide turned against the U-boats, which suffered catastrophic losses. Nonetheless Dönitz rose to become commander-in-chief of the entire German navy in 1943, retaining Hitler's confidence to the end.
In his final testament before his suicide, Hitler named Dönitz his successor as head of state. For a few chaotic days in May 1945 the admiral presided over the collapsing Reich and authorized the unconditional surrender that ended the war in Europe. Tried at Nuremberg, he was convicted of war crimes and served ten years in prison. He died in 1980, an unrepentant defender of his wartime record.