<P> Hansell's successor, Major General Curtis LeMay, assumed command in January 1945 and initially continued to use the same precision bombing tactics, with equally unsatisfactory results . The attacks initially targeted key industrial facilities but much of the Japanese manufacturing process was carried out in small workshops and private homes . Under pressure from United States Army Air Forces (USAAF) headquarters in Washington, LeMay changed tactics and decided that low - level incendiary raids against Japanese cities were the only way to destroy their production capabilities, shifting from precision bombing to area bombardment with incendiaries . Like most strategic bombing during World War II, the aim of the air offensive against Japan was to destroy the enemy's war industries, kill or disable civilian employees of these industries, and undermine civilian morale . </P> <P> Over the next six months, the XXI Bomber Command under LeMay firebombed 67 Japanese cities . The firebombing of Tokyo, codenamed Operation Meetinghouse, on March 9--10 killed an estimated 100,000 people and destroyed 16 square miles (41 km) of the city and 267,000 buildings in a single night . It was the deadliest bombing raid of the war, at a cost of 20 B - 29s shot down by flak and fighters . By May, 75% of bombs dropped were incendiaries designed to burn down Japan's "paper cities". By mid-June, Japan's six largest cities had been devastated . The end of the fighting on Okinawa that month provided airfields even closer to the Japanese mainland, allowing the bombing campaign to be further escalated . Aircraft flying from Allied aircraft carriers and the Ryukyu Islands also regularly struck targets in Japan during 1945 in preparation for Operation Downfall . Firebombing switched to smaller cities, with populations ranging from 60,000 to 350,000 . According to Yuki Tanaka, the U.S. fire - bombed over a hundred Japanese towns and cities . These raids were devastating . </P> <P> The Japanese military was unable to stop the Allied attacks and the country's civil defense preparations proved inadequate . Japanese fighters and antiaircraft guns had difficulty engaging bombers flying at high altitude . From April 1945, the Japanese interceptors also had to face American fighter escorts based on Iwo Jima and Okinawa . That month, the Imperial Japanese Army Air Service and Imperial Japanese Navy Air Service stopped attempting to intercept the air raids in order to preserve fighter aircraft to counter the expected invasion . By mid-1945 the Japanese only occasionally scrambled aircraft to intercept individual B - 29s conducting reconnaissance sorties over the country, in order to conserve supplies of fuel . In July 1945, the Japanese had 1,156,000 US barrels (137,800,000 l) of avgas stockpiled for the invasion of Japan . About 604,000 US barrels (72,000,000 l) had been consumed in the home islands area in April, May and June 1945 . While the Japanese military decided to resume attacks on Allied bombers from late June, by this time there were too few operational fighters available for this change of tactics to hinder the Allied air raids . </P> <P> The discovery of nuclear fission by German chemists Otto Hahn and Fritz Strassmann in 1938, and its theoretical explanation by Lise Meitner and Otto Frisch, made the development of an atomic bomb a theoretical possibility . Fears that a German atomic bomb project would develop atomic weapons first, especially among scientists who were refugees from Nazi Germany and other fascist countries, were expressed in the Einstein - Szilard letter . This prompted preliminary research in the United States in late 1939 . Progress was slow until the arrival of the British MAUD Committee report in late 1941, which indicated that only 5 to 10 kilograms of isotopically enriched uranium - 235 were needed for a bomb instead of tons of natural uranium and a neutron moderator like heavy water . </P>

Who ordered the attack on hiroshima and nagasaki