During the Second Sino-Japanese War (1937–1945), which is often regarded as the beginning of World War II, the ROCAF participated in attacks on Japanese warships on the eastern front and along the Yangtze river and interdiction and close-air support during the Battle of Shanghai in 1937. Chinese sources estimated the Japanese could field approximately 600 aircraft (from a total of 1,530) against China's 230 combat-ready aircraft. As the Imperial Japanese Army Air Service and the Imperial Japanese Navy Air Service conducted mass-terror bombings against both civilian and military targets, the Chinese Air Force also planned raiding Japanese home island with the Martin B-10 bomber that was suited for the trans-oceanic raid.