When Preparations completed in August 1940

Where Southeast English coast from Ramsgate and Dover (county Kent) in the north to Portsmouth (county Sussex) and Devon in the south, as well as the Isle of Wight off the south coast of Hampshire

Sea Lion Invasion Map

Who Staff of the Oberkommando der Wehrmacht (OKW) (English: Supreme Command of the Armed Forces), Army Group A under Field Marshal Gerd von Rundstedt (1875–1895), and Army Group C under Field Marshal Wilhelm von Leeb (1876–1956). Plans called for an amphibious landing with around 67,000 men in the first echelon and an airborne division to support them.

Why Britain’s ally France officially surrendered to Hitler’s invading forces on June 22, 1940, in the full glare of German media in the same railroad car where Kaiser Wilhelm II’s representatives had signed the World War I surrender document 21 years before. The refusal of Britain to negotiate an end to European hostilities prompted Hitler to plan for an airborne and amphibious invasion of England to eliminate that country’s ability to interfere with German military and political hegemony in Europe.

What On July 16, 1940, Hitler issued Fuehrer Directive 16, setting in motion preparations for Operation Sea Lion (Unternehmen Seeloewe). Sea Lion called for landings on the south coast of England, backed by an airborne assault. But to have had any chance of success, the operation would have required air and naval supremacy over the English Channel. Col-Gen. Alfred Jodl, Chief of Operations in the OKW; Grand Admiral Erich Raeder, commander-in-chief of the Kriegsmarine; and Air Marshal Hermann Goering expressed reservations at one time or other as to whether Germany would every have mastery over the English Channel or in English skies. With the Luftwaffe’s inability to deliver a knockout punch to the Royal Air Force during the Battle of Britain (June–September 1940), Sea Lion was postponed indefinitely on September 17, 1940.

Outcome Had Operation Sea Lion succeeded, Britain and Ireland would have been divided into six military-economic commands. Over 2,800 people would have been arrested immediately, and the occupation authorities would begin liquidating Britain’s Jewish population, which numbered over 300,000. The able-bodied male population between the ages of 17 and 45 would for the most part be interned and dispatched to the Continent. This represented about 25% of the British population. Britain was then to be plundered for anything of financial, military, industrial, or cultural value. Following Hitler’s postponement of the invasion, a palpable sense of relief swept over the Wehrmacht. Army Group A commander Field Marshal Gerd von Rundstedt took this view. Sea Lion was resched­uled for some time the next year but it was not until February 13, 1942, long after Operation Barbarossa had been unleashed on the Soviet Union, that forces earmarked for the Sea Lion were released to other duties.

Alternate History: Operation Sea Lion, the Successful German Invasion and Occupation of England