The Imperial German Navy or the Imperial Navy (German: Kaiserliche Marine) was the navy of the German Empire, which existed between 1871 and 1919. It grew out of the small Prussian Navy (from 1867 the North German Federal Navy), which was mainly for coast defence. Kaiser Wilhelm II greatly expanded the navy. 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.