Operation Sealion Operation Sealion was the planned but ultimately cancelled cross - Channel invasion of Great Britain by Nazi Germany during World War II . ( PROSE : " " ) Background . After the outbreak of World War II in Europe following the invasion of Poland in September 1939 , Germany offered to negotiate peace with the United Kingdom and France in October . The Allies refused . Germany thus launched a " lightning war " against Western Europe , defeating France , Belgium and the Netherlands by the summer of 1940 . ( PROSE : " Just War " , " " , AUDIO : " Just War " ) Thousands of British soldiers were successfully evacuated back home from mainland Europe after they were cut off by the Wehrmacht at Dunkirk . ( PROSE : " " , TV : " Co - Owner of a Lonely Heart " , AUDIO : " The Nemonite Invasion " ) The Germans proceeded to occupy the Channel Islands , the only British territory to fall under German control during the war . ( PROSE : " Just War " , " Illegal Alien " , AUDIO : " Just War " ) Hitler ' s ultimate aim for Germany was to push eastwards into Russia , Persia and Asia . Operation Sealion was Germany ' s plan to knock Britain out of the war and end hostilities in the west by invading England before moving into the east . ( PROSE : " " ) British defensive measures . The British feared that the Germans would invade daily . ( TV : " Victory of the Daleks " ) Winston Churchill was distraught after the fall of Europe but the Doctor convinced him to continue the fight . ( AUDIO : " The Ultimate Adventure " ) Civilian volunteers signed up to the Home Guard to help fend off an invasion . ( PROSE : " Losing the Audience " ) Hidden bases full of supplies and weapons were established to allow a British resistance movement to operate against a German occupation . ( PROSE : " Made of Steel " ) Four citadels were build under the surface of London , intended to allow the British government to continue operations if events took a turn for the worse . ( AUDIO : " The Fifth Citadel " ) The government continued to meet in the Cabinet War Rooms while London was under German bomb ardment . The Eleventh Doctor claimed that Britain ' s continued resistance was watched closely by the whole world and acted as a " beacon of hope " for the conquered nation s . ( TV : " Victory of the Daleks " ) The extra - dimension al Shaker s approached the desperate British government and offered them aid in return for " Lebensraum " . The British planned Operation Shaker , a guerilla war against the Germans , which was ultimately never put into effect . ( PROSE : " Losing the Audience " ) The Dalek s also approached the government , passing themselves off as friendly combat servant robot s known as Ironsides , as part of a ploy to rebuild their race . ( TV : " Victory of the Daleks " ) German preparatory attacks . The Germans embarked on a number of smaller operations to prepare for an invasion , or to bring the British to the negotiating table before an invasion became necessary . In the summer of 1940 , Hermann Goering ' s Luftwaffe faced the Royal Air Force in the Battle of Britain but were repelled before they could achieved air superiority , ( PROSE : " / Carpenter / Butterfly / Baronet / " ) for which Hitler never forgave them . ( PROSE : " The Shadow in the Glass " ) In late 1940 , Germany began an aerial bombardment campaign against British cities which became known as the Blitz . German propaganda claimed the attacks were only directed against military and industrial targets . ( PROSE : " Just War " , AUDIO : " Just War " ) However , civilians suffered under the bombardment . Many people slept in bomb shelters or underground stations during the night ( PROSE : " Illegal Alien " , " Tell Me You Love Me " , TV : " The Empty Child " / " The Doctor Dances " ) and women and child ren were evacuated to the safety of the countryside . ( TV : " The Doctor , the Widow and the Wardrobe " , " Ghost Machine " , " Lost in Time " ) The Blitz was effectively over by July 1941 . ( PROSE : " Illegal Alien " ) In June 1941 , a small group of Germans led by Lieutenant Koenig and aided by their spy , Miss Wyckham , landed on the south coast of England . They attempted to use a piece of Chronosteel to block the British early warning system but were thwarted when Clyde Langer and George Woods rang the village church bell s , alerting the Home Guard . ( TV : " Lost in Time " ) Cancellation . After continued failure to bring Britain to heel , Germany turned her attention towards Eastern Europe and launched Operation Barbarossa against the Soviet Union in June 1941 , relieving Britain of much of the pressure brought on by the threat of invasion . ( PROSE : " Losing the Audience " ) Despite the tremendous start to the campaign , the Germans quickly began to push beyond their capabilities . In December , the onset of winter brought their advance to a halt before they reached Moscow . A counterattack by the Red Army led to Germany ' s first major defeat of the war . The need to stabilise the Eastern Front , plus the entry of the United States into the war , forced the Germans to conserve many of their resources and divert them to the more pressing theatres of war . Consequently , they ceased their aerial bombardment campaigns against Britain and abandoned their plans to invade . ( PROSE : " Just War " )