The battle began in mid-July and, initially, the Luftwaffe concentrated on attacking shipping in the English Channel and attacking coastal towns and defences. From 12 August, Goering shifted his focus to the destruction of the RAF, attacking airfields and radar bases. Convinced that Fighter Command was now close to defeat, he also tried to force air battles between fighter planes to definitively break British strength. However, Goering grew frustrated by the large number of British planes that were still fighting off his attacks. On 4 September, the Luftwaffe switched tactics again and, on Hitler's orders, set about destroying London and other major cities. Eleven days later, 15 September 1940,on what became known as 'Battle of Britain Day', the RAF destroyed the huge incoming Luftwaffe formations in the skies above London and the south coast.
It was now clear to Hitler that his air force had failed to gain air superiority so, on 17