Corpses of suffocated Chongqing residents lie outside the Jiaochangkou air-raid shelter. On June 5, 1941, the Japanese flew more than 20 sorties against Chongqing, bombing the city for 3 hours. About 2,500 civilians were asphyxiated when the crowds rushed to return to the inadequate number of shelters. The bombing was part a Japanese air campaign targeting the Chinese Kuomintang provisional capital of Chongqing. A total of 268 air raids were conducted against Chongqing from February 18, 1938 to August 23, 1943. The bombing sorties numbered at more than 6,800, with more than 11,500 bombs dropped, mainly incendiary bombs. The targets were usually residential areas, business areas, schools, hospitals, focusing on non-military targets. Since 1999 the city sonuds an air raid siren every June 5 to commemorate the tragedy.