Hitler never grasped naval affairs and sea power
Adolf Hitler failed to initiate Operation Sea Lion, the proposed invasion of Great Britain, because he lacked the naval power to gain control of the British Channel for the necessary time to execute the operation. At the same time, though the U-Boats gained significant successes against the supply convoys keeping England alive, he lacked the ability to disrupt the British further using surface ships. Several powerful surface units existed, but after the loss of the Graf Spee and Bismarck, Hitler demanded that the surface ships be kept for the most part in port, not wanting to have another loss damaging German morale. The aircraft carrier under construction was suspended.
Had Hitler allowed Plan Z to be completed, which would have provided the Germans with several additional, powerful, capital ships, prior to starting the war in Europe, the German Navy would have been in a better position to contest the mastery of the seas around Europe, especially being supported by the Italian Navy and the captured ships of the French Navy. Hitler was a soldier in the First World War, and he had a soldier’s contempt of ships and the sea, focused on the land operations on the continent. The German Navy attempted to fight for control of the sea almost exclusively with U-Boats, and as the Allies adopted new techniques to fight them, the Battle of the Atlantic was lost.