On 8 March LeMay issued orders for a major firebombing attack on Tokyo the next night . The raid was to target a rectangular area in northeastern Tokyo designated Zone I by the USAAF which measured approximately by . This area was divided by the Sumida River , and included most of Asakusa , Honjo and Fukagawa Wards . These wards formed part of the informally-defined Shitamachi district of Tokyo , which was mainly populated by working-class people and artisans . With a population of around 1.1 million , it was one of the most densely populated urban areas in the world . Zone I contained few militarily significant industrial facilities , though there were a large number of small factories which supplied Japan 's war industries . The area was highly vulnerable to firebombing , as most buildings were constructed from wood and bamboo and were closely spaced . Due to this vulnerability , it had suffered extensive damage and heavy casualties from fires caused by the 1923 Great Kantō earthquake . The United States ' intelligence services were aware of how vulnerable the region remained to fire , with the Office of Strategic Services rating it as containing the most combustible districts in Tokyo
1923 Great Kantō earthquake
1923 Great Kantō earthquake
Bombing of Tokyo (10 March 1945)