The key leader was Admiral Alfred von Tirpitz, who greatly expanded the size and quality of the navy, while adopting the sea power theories of American strategist Alfred Thayer Mahan. The result was a naval arms race with Britain as the German navy grew to become one of the greatest maritime forces in the world, second only to the Royal Navy. The German surface navy proved ineffective during World War I; its only major engagement, the Battle of Jutland, was indecisive.