Operation Sea Lion was the German plan for the invasion of the British Isles. The plan was to beat down the Royal Air Force (RAF) engage the Royal Navy in the Atlantic and the Mediterranean and sweeps the English Channel of mines and then invade. The planned air battle had four phases: Attack British shipping in the Channel; attack British coastal air fields; attack inland air fields and radar installations; attack towns and cities. Control of the air with the destruction of the RAF was deemed necessary as a prelude to invasion. On August 25th a German bomber pilot, off course, erred and bombed London with the RAF launching a retaliatory attack against Berlin. This changed the air war and the RAF, while outnumbered, fought the Luftwaffe to a standstill inflicting heavy losses. On September 1940 the Battle Britain basically ended with Operation Sea Lion indefinitely postponed.