(in World War II) Attacks by bomber aircraft on military and civilian targets. As part of his Blitzkrieg tactics, Hitler deployed dive-bombers in the offensives in Poland (1939) and western Europe (1940). In August 1940 the first major German offensive was launched against Britain, a series of daylight attacks by bombers, many of which were destroyed by fighter aircraft of the Royal Air Force in the Battle of Britain. A German night-bombing offensive on civilian targets then began which lasted until May 1941. The Allied air offensive against Germany and the occupied countries grew in intensity throughout the war. The development of radar to intercept aircraft and direct gunfire revolutionized the Allied bombing offensive. Increasing resources were made available to the British Bomber Command under Air Marshal Sir Arthur Harris, and daylight raids by the US Air Force, combined with British night-bombing, endeavoured to obliterate key German cities. Meanwhile the bulk of German bombing power was turned to the Eastern Front, where fighter-bombers supported the army, attacking besieged cities, such as Leningrad and Stalingrad. Pilotless flying bombs (V1s) and rocket missiles (V2s), launched against southern England during 1944 and 1945, did relatively little damage. In the Far East a massive bombing offensive was launched by US forces against Japanese cities in October 1944. On 6 and 9 August 1945 respectively, US aircraft dropped the world’s first atomic bombs on the Japanese cities of Hiroshima and Nagasaki, bringing the war against Japan to a close.