During the Sino-Japanese War (1937-1945), the ROCAF participated in attacks on Japanese warships on the eastern front and along the Yangtze river including interdiction and close-air support for the Battle of Shanghai in 1937. The Chinese frontline fighter aircraft initially comprised mainly of the Curtiss Hawk II and III's and the Boeing P-26C model 281, and engaged Japanese fighters in many major air battles beginning on the 14th of August 1937, when Imperial Japanese Navy warplanes raided Chienchiao airbase; "814" has thus become known as "Air Force Day". Chinese Boeing P-26/281 fighters engaged Japanese Mitsubishi A5M fighters in what was the world's first instances of aerial dogfighting and kills between all-metal monoplane fighter aircraft. A unique mission in April 1938 saw two Chinese Martin B-10 bombers fly a mission over Japan, but dropping only anti-war leaflets over the Japanese cities of Nagasaki and Saga. It was a war of attrition for the Chinese pilots, as many of their most experienced ace fighter pilots, such as Lieutenant Liu Tsui-Kang and Colonel Kao Chih-Hang were lost. A half-year into this second Sino-Japanese War, which is considered the beginning of World War II in Asia, the Chinese Air Force inventory of frontline American Hawk II and III's and P-26C/281's were soon superseded by faster and better armed Russian-made Polikarpov I-15's and I-16's as support from the Soviet Union became greatly augmented and American support faded.
Through attrition and loss of their most experienced fighter pilots in the first half of the Second Sino-Japanese War, the Republic of China Air Force ultimately suffered irreversible losses in combat against the Japanese, and by the beginning of 1942 the ROCAF was practically annihilated by Japanese aircraft, particularly with the introduction of what was then the most advanced fighter-aircraft in the world; the Mitsubishi Zero. The ROCAF was eventually supplemented with the establishment of the Flying Tigers and very heavily armed and armored Curtiss P-40 Warhawks, and subsequently rebuilt each year following Imperial Japan's attack on Pearl Harbor with new aid and vigor from the United States.
The Sino-Japanese War started on the 7th July, 1937. At that time Chinese sources estimated that the Japanese could field approximately 600 aircraft (from a total of 1,530) against China’s 230 combat aircraft. During the first phase up to 1939, aerial bombing of enemy bomber formations was tried with indifferent results,and leaflet-dropping raids carried out over Japanese cities. The Japanese bombing raids were also fiercely contested, sometimes with significant Japanese losses. After suffering heavy losses in the Battle of Wuhan in October 1938, most airforce units were withdrawn for reorganisation and training.
It was reconstituted into seven Groups, one separate Squadron and four Volunteer Groups. In 1940 the Russian Volunteer Group was stood down. By the end of 1941 the airforce had 364 operational aircraft of which 100 P-40s were operated by the American Volunteer Group.US replacement aircraft began to arrive in March 1942.They included A-29, P-40, P-43, and P-66 types, and in 1945 B-25s,B-17s and P-51Bs and Ds.
In 1944, the USAAF 15th Airforce commenced joint operations in the China theatre. By this time the Chinese Airforce was mostly equipped with current operational aircraft types and was superior in all respects to the opposing Japanese air forces which remained.
(this is an incomplete list and will be expanded)
The entry of the USA into the war with Japan at the end of 1941 led to the receipt of Lend-Lease equipment from the United States, including aircraft. American Lend-Lease aviation equipment had already begun to arrive in China as early as the middle of 1941, though that includes the first shipments before January 1942 which arrived under the guise of purchases. Including previously purchased American aircraft, US soon replaced USSR as the largest supplier for the Chinese Nationalist air force during the war (Including the Second Sino-Japanese War that actually broke out in 1931 when Japan invaded Manchuria). The US aircraft supplied to China in its struggle against the Japanese invaders included: A-12, A-17, A-19, A-29, B-10, B-17, B-24, B-25, B-29, C-19, C-43, C-45, C-46, C-47, C-100 (Gamma 2E light bomber version), Curtiss F11C Goshawk, P-12, P-26, P-36, P-38, P-40, P-43, P-47, P-51,P-61, P-66, and PB4Y.
Retraining on American aircraft occurred for the most part in India. (Karachi and other cities), where Chinese pilots were sent both as groups and as entire units. As early as the end of 1941 Chinese pilots, mainly recently graduated from flight schools, began to be sent to the USA for longer training and mastery of American aircraft.
The first American P-43A fighters were received by the 4th Air Group (21st - 24th Squadrons) in March 1942. They retrained in Kunming, but for the new aircraft the pilots sequentially flew in small groups to India. On 24 April the deputy commander of the 24th Squadron, Wu Zhenhua, crashed on the flight to Kunming. On 12 May, Chen Lokun, the flight commander of the 24th Squadron was killed during a training flight, crashing into a tree during landing. In July for unclear reasons the P-43 of the 4th Air Group commander, Zheng Shaoyu, caught fire in the air and the pilot was killed. On 3 August 1942 during a training flight the deputy group commander Chen Sheng crashed. A similar series of crashes accompanied the mastery by the Chinese of almost every new machine. (It is notable that in Chinese sources the family names are given only of the perished commanders of various ranks, while the losses amongst the line pilots are hardly even noted.) Concluding their conversion to the P-43A in early August 1942, the group returned to Chengdu.
In February 1943, preparing for transition to the new American air equipment, the Chinese transferred to India the primary training groups from their flight schools. Only training for reconnaissance and photography continued to be carried out in China. In March 1945 the cadets completing primary training in India were sent to America to train further. By that time the number of cadets dispatched had reached 1224, of whom 384 managed to return to China and participate in combat. In all, from 1942 to 1945 420 training aircraft were sent from the USA to China through India, including 20 AT-6, 8 AT-7, 15 AT-17, 150 PT-17, 127 PT-19, 70 PT-22, and 30 BT-13, and also 10 Beechcraft D-17 medical aircraft.
Following the failure of Hawk 75 production, the aviation factory planned to organize assembly of the export version of the Curtiss-Wright CW-21 Demon, light fighter. Three aircraft and 32 sets of components were ordered from the USA. The factory at Leiyun worked until April 1942, when on account of Japanese attacks it had to be evacuated to Kunming. From 1943 to 1946 the aircraft factory, which was dispersed in the ravines neighboring Kunming, assembled an experimental series of nine fighter monoplanes, probably from components of the Hawk 75M and 75A-5, and CW-21. To a degree they were similar to the American prototypes and their further fate is unknown. In western sources the first example figures under the strange designation XP-0.