World War II: Due to setbacks in the Battle of Britain and approaching autumn weather, Hitler postpones Operation Sea Lion.

The Battle of Britain was a military campaign of the Second World War, in which the Royal Air Force (RAF) and the Fleet Air Arm (FAA) of the Royal Navy defended the United Kingdom against large-scale attacks by Nazi Germany's air force, the Luftwaffe. It was the first major military campaign fought entirely by air forces. It takes its name from the speech given by Prime Minister Winston Churchill to the House of Commons on 18 June: "What General Weygand called the 'Battle of France' is over. I expect that the Battle of Britain is about to begin."

Operation Sea Lion, also written as Operation Sealion, was Nazi Germany's code name for their planned invasion of the United Kingdom. It was to have taken place during the Battle of Britain, nine months after the start of the Second World War. Following the Battle of France and that country's capitulation, Adolf Hitler, the German Führer and Supreme Commander of the Armed Forces, hoped the British government would accept his offer to end the state of war between the two. He considered invasion to be a last resort, to be used only if all other options had failed.