On 5 June 1941, in midst of the increased brutality of the new ""Operation 102"" ("102"号作战) bombing campaign to capitulate China's war of resistance, the Japanese flew more than 20 sorties, bombing the city for three hours. About 4,000 residents who hid in a tunnel were asphyxiated. With the start of full-scale war between the Soviet Union and Nazi Germany on 22 June 1941, and with Generalissimo Chiang Kai-shek looking for increased support from the Americans through the Lend-Lease Act of which was extended to China on 06 May 1941, all new fighter aircraft produced by the Soviets were now directed to the battlefronts against Nazi Germany.