August 6, 1945, was a clear, blue Monday morning in the city of Hiroshima. At 7:09 air raid sirens shattered the morning air as allied weather planes flew over, driving a city of around 345,000 people indoors and into shelters. About 15 minutes later, the planes left, the skies emptied and the all-clear sounded; Hiroshima woke back up and started their Monday over again.