Operation Sea Lion (German: Unternehmen Seelöwe) was Nazi Germany's code name for a provisionally proposed invasion of the United Kingdom during the Battle of Britain in the Second World War. Following the Fall of France the Nazis expected the British to seek a peace agreement, and invasion was considered as a last resort if other options failed. As a precondition, the proposed operation required both air and naval superiority over the English Channel and proposed landing sites, neither of which the Germans ever achieved during the war. A large number of barges were adapted as the proposed invasion fleet, but Sea Lion was postponed indefinitely on 17 September 1940 and never carried out. The German High Command had no confidence that the plan was feasible, and most historians agree it had