The Second Sino-Japanese War began on 7 July 1937 with the Marco Polo Bridge incident in the Republic of China and is described by some historians as the start of World War II, as full-scale warfare erupted with the Battle of Shanghai, and ending when the Empire of Japan surrendered to the Allies in August 1945. The Chinese Air Force faced the Imperial Japanese Army and Navy Air Forces and engaged them in many aerial interceptions, including the interception of massed terror-bombing strikes on civilian targets, attacking on each other's ground forces and military assets in all manners of air interdiction and close air support; these battles in the Chinese skies were the largest air battles fought since World War I, and featured the first-ever extensive and prolonged deployment of aircraft carrier fleets launching preemptive strikes in support of expeditionary and occupation forces, and demonstrated the technological shift from the latest biplane fighter designs to the modern monoplane fighter designs on both sides of the conflict.

Overview China was not an aviation-industrial power at the time, and relied on foreign countries for its military aircraft, but did have a fledgling aircraft industry that produced a few indigenous experimental aircraft designs and foreign aircraft designs under license, including about 100 Hawk III fighter-attack planes, China's frontline fighter-attack plane of choice when war broke out in 1937, at the CAMCO plant based at the Hanzhou Jianqiao Aerodrome. 15 Chinese-American pilots along with Chinese pilots of other foreign nationalities formed the first unofficial volunteer group of pilots to join provincial/warlord air force units in the early-mid 1930s, and ultimately integrating into the front-line air units of the centralized command of the Nationalist Air Force of China by 1937, in the unified-front for imminent war against Imperial Japan. These volunteers included future ace-fighter pilots Art Chin, John "Buffalo" Huang, Wong Pan-Yang, plus Hazel Ying-Lee (who was not allowed to fly in combat as a female), Louie Yim-qun, Chan Kee-Wong et al.

As the battles of Shanghai, Nanjing, Taiyuan, and other regions dragged on near the end of 1937, the initial Chinese Air Force inventory of mostly American-made aircraft had become largely depleted, and the Soviet Union came to China's aid by supplying the bulk of aircraft to the Chinese Air Force for the next four years of war under the Sino-Soviet Treaty of 1937, and dispatching a Soviet Volunteer Group of aviators to assist with the combat operations in China; Chinese fighter pilots having mostly converted into the Polikarpov I-15 and I-16 series of fighter aircraft by early-1938. According to records from the USSR, 563 fighter planes and 322 bombers were provided to China by the Soviet Union, and these included the twin-engined Tupolev SB medium bombers and 4-engined Tupolev TB-3 heavy bombers, with the addition of Polikarpov I-153 fighters; the Chinese Air Force would remain with these increasingly obsolescent aircraft through 1941 as the Japanese made tremendous technological advancements to their combat aircraft designs and powerplant technology.Soviet Fighters in the Sky of China (1937-1940), by Anatolii Demin and A. Kosmonavtika.Soviet Fighters in China Soviet Bombers in China (1937-1940), by Anatolii Demin and Vladimir Kotel'nikov.Soviet Bombers in China Soviet Fighters in the Sky of China IV (1937-1940), by Anatolii Demin and A. Kosmonavtika.Soviet Fighters in China IV

Following the Japanese invasion of French Indochina, the United States took actions to assist the Republic of China against Imperial Japan, with the oil and scrap metal embargo and freezing of Japanese assets in the summer of 1941, and along with the Lend-Lease Act of which China was included as a beneficiary on 6 May 1941, the American Volunteer Group (a.k.a. "Flying Tigers") entered the war in December 1941 with the task of protecting the main Allied supply-line into China; the cross-Himalayan air-route known as "The Hump", between the Harbor of Rangoon in Burma, British bases in India, and the Chinese wartime port-of-entry in Kunming, China, and consequently, with the attack on Pearl Harbor, the U.S. officially joined the war against Japan.

1937 Battle of Shanghai/Nanjing

At the outbreak of full-scale conflict of the Second Sino-Japanese War/World War II in August 1937, the Chinese Air Force had 645 combat aircraft, of which about 300 were fighter planes. Japan had 1,530 army and navy aircraft, of which about 400 were deployed in China.Air Warfare: an International Encyclopedia Vol. 1, 2000, edited by Walter J. Boyne, (e-book), pp. 125–127.Air Warfare: The frontline Chinese fighter squadrons were equipped primarily with the Curtiss Hawk IIIs and Hawk IIs, followed by Boeing P-26 Model 281 Peashooter, and Fiat CR.32. Bomber-attack aircraft consisted primarily of the Curtiss A-12 Shrikes, Douglas O-2s, Heinkel He 111, Martin B-10s and Northrop Gammas. The air war in China had become a testing-zone for the latest biplane fighter designs confronting the new generation of monoplane fighter and bomber aircraft designs; the world's first aerial combat and kills between modern monoplane fighter would occur in the skies of China.

In August 1937 Claire Lee Chennault accepted the offer to assume position as an "air combat adviser"Air Warfare: an International Encyclopedia Vol. 1, 2002, edited by Walter J. Boyne, (e-book), Chennault, p. 124.Air Warfare: of Chiang Kai-shek, and to train new fighter pilots at the Republic of China Air Force Academy, which was forced to move from the Jianqiao to the Wujiaba Aerodrome due to the war situation.

On 14 August 1937 the Chinese Air Force fighter squadrons sortied for the defense of Shanghai and Nanjing, capital of the Republic of China. In the afternoon of 14 August 1937, two groups of nine Japanese Mitsubishi G3M long-range bombers were launched from Japanese Taiwan on a mission to bomb Jianqiao Airfield in Hangzhou, Zhejiang, and Guangde Airfield in Anhui. The 21st and 23rd Squadrons, led by Kao Chih-hang, the Group Commander of the Chinese 4th Pursuit Group, took off from Jianqiao Airfield to intercept the Japanese bombers, despite the fact that some of the fighters had just flown in from Zhoukou and had not been refueled. Kao attacked a G3M bomber and scored a direct hit sending it plummeting to the ground in flames, and he also damaged another G3M bomber; it was the first air-to-air victory for the Chinese Air Force. Meanwhile, three other Hawk IIIs attacked a third G3M bomber and shot it down. The second group of Japanese G3M bombers attacking Guangde Airfield was intercepted by the 22nd Squadron of the 4th Pursuit Group and the 34th Squadron. Squadron Commander Cheng Hsiao-yu of the 22nd Squadron shot up the right engine and the wing fuel tank of one G3M bomber, forcing it to ditch before returning to its air base. The aerial battles in the afternoon of 14 August were a resounding victory for the Chinese Air Force, in which the Chinese Hawk III fighters destroyed four Japanese G3M long-range bombers without losing a single plane to the Japanese. In addition, two G3Ms were also shot down by ground anti-aircraft fire.

On the following day at dawn 15 August, 12 Japanese Type 89 torpedo bombers were intercepted over Hangzhou by 21 Hawk IIIs of the Chinese 4th Pursuit Group led by Group Commander Kao Chi-hang. The Chinese shot down eight bombers. In the afternoon 20 Japanese G3M bombers on a raid to Nanjing were intercepted by 26 Chinese fighters from the 8th, 17th, 28th and 34th Squadrons flying eight Boeing 281 P-26 Peashooters, five Gloster Gladiators, 13 Hawk IIIs and Hawk IIs. The Chinese shot down four and damaged six Japanese G3M bombers.

On 16 August, the Japanese launched two raids with a total of 11 Japanese G3M bombers on the airfield near Nanjing; they were intercepted by five Chinese fighters from the 17th and 28th Squadrons. The Chinese shot down three Japanese bombers, and lost three fighters. On 17 August Chinese Hawk III fighters flew 17 sorties shooting down one Japanese bomber; the Chinese lost two aircraft. From 20 August to the end of the month, daily aerial engagements took place between the Chinese and Japanese planes, and the Japanese facing unexpected tenacity from the Chinese pilots, suffered prohibitive losses made worse by the sacrifice of armored protection in exchange for supposed-advantage of lighter-weight and higher-performance of the newer Japanese aircraft designs. In that period the Chinese shot down 24 Japanese planes and lost 11 aircraft.

In order to compete against the highly advanced Mitsubishi A5M fighters of the IJNAF, Colonel Kao Chih-hang ordered maintenance crews to remove the bomb-racks, fuel tank cowlings, and landing lights to save weight and reduce drag off the Hawks. On 12 October 1937, Kao led an aggressive seek-and-destroy mission consisting of six Hawk IIIs, two Boeing P-26/281 "Peashooters", and a Fiat CR.32 to engage approaching Japanese fighter aircraft. A group of Mitsubishi A5Ms soon appeared on approach to Nanking and Col. Kao led his group into a melee, where Maj. John Wong Pan-Yang, a Chinese-American volunteer pilot from Seattle flying one of two P-26 "Peashooters", drew first blood shooting down the A5M piloted by PO1c Mazazumi Ino. Captain Liu Cuigang shot down another A5M that was sent crashing down into a "Mr. Yang's residence in southern Nanking", and Colonel Gao scored a double-kill against the A5Ms, including that of shotai leader WO Torakuma. The outnumbered Chinese pilots were able to defeat the Japanese fighter group flying the technologically superior Mitsubishi A5M "Claudes".

Battle of Taiyuan

As the frontline battlefields raged at the Battle of Shanghai and Battle of Nanking, pressing demands for aerial support at the Battle of Taiyuan in the northern front and Canton in the southern front, forced the Chinese Air Force to split the 28th PS, 5th PG based at Jurong Airbase in the Nanking defense sector into two smaller squadrons, and then dispatching half of the squadron to the south in Guangdong under the command of Lt. Arthur Chin, and the other half to the north at Taiyuan under the command of Capt. Chan Kee-Wong. Battle of Nanchang The Japanese launched pre-emptive airstrikes against Chinese Air Force assets at the Laoyingfang and Qingyunpu Airbases beginning in 1937; these were engaged by new Chinese Polikarpov fighters obtained under the Sino-Soviet Non-Aggression Pact of 1937. Summary of 1937 In the first four months of the war from July to November 1937, the Chinese Air Force flew 137 sorties, attacking Japanese army positions, and engaged in 57 air battles with Japanese airplanes; the Chinese Air Force shot down 94 Japanese planes and damaged 52 on the ground, but lost 131 aircraft.China and the United States: a new Cold War History, 1998, p. 264, edited by Xiaobing Li, Hongshan Li, University Press of America, The Chinese Air Force pilots fought well despite their airfields being under constant Japanese air attacks. To commemorate the heroic acts and sacrifices of the Chinese pilots in defense of their homeland, the Republic of China declared 14 August the Chinese Air Force DayFly Boys of Generalissimo, by Samuel Hui.Fly Boys of Generalissimo known as the "814 Day", the day on which the Chinese Air Force scored its first air-to-air victory. In this initial phase of the war, the outnumbered Chinese had no replacements for their lost planes and many experienced pilots killed in action, while the Western powers turned its back to the war situation, the Chinese began turning to the Soviet Union for new aircraft and various other combat equipment and war materials, while the Japanese were able to replace their lost planes with even more advanced aircraft, and continued to train new pilots.

1938 Battle of Taierzhuang

Chinese B-10 bombers over Nagasaki