World War II, on the other hand, led to unparalleled social and political upheaval. Although Penang Island had been designated as a fortress, Penang fell to the Imperial Japanese Army on 19 December 1941, after suffering devastating aerial attacks. The British covertly evacuated Penang's European populace; historians have since contended that "the moral collapse of British rule in Southeast Asia came not at Singapore, but at Penang".Penang Island was subsequently renamed "Tojo-to", after Japanese Prime Minister Hideki Tojo. The period of Japanese occupation was renowned for the Imperial Japanese Army's massacres of Penang's Chinese populace, known as "Sook Ching" to the locals. Women in George Town were also coerced to work as comfort women by the Japanese. Meanwhile, the Port of Penang was put to use as a major submarine base by the Axis Powers.