Resistance was put up by the Chinese Air Force and the National Revolutionary Army's anti-aircraft artillery units in defense of the provisional wartime capital of Chongqing and other targets in Sichuan.

While the Chinese victory at the Battle of Kunlun Pass kept the Burma Road open, the ever increasing Japanese blockade of imports into China, particularly after Chongqing was cut off from the sea after losing Nanning in the Battle of South Guangxi, and with war now looming in Europe, the supplies needed by the Chinese were barely trickling in, and the Chinese Air Force had to make do with the increasingly poor flying performance and maintenance problems of these Soviet-made fighters burning low-grade 65–75 octane fuel in the first few years defending Chongqing and Chengdu while massive formations of Japanese aircraft benefiting from great technological advancements and burning 90+ octane fuel were flying ever-faster and higher, almost beyond practical reach of the obsolescent Chinese fighter aircraft; the British Royal Air Force for example were supplied directly by their own aircraft industry while benefiting from tremendous improvements in their fighter aircraft speed, acceleration and high-altitude performance by upgrading from the standard 87 octane fuel to the "secret 100 octane" formula later in the Battle of Britain.

The exploratory strikes on Chongqing began on 18 February 1938, and continued sporadically at relatively low intensity until the commencement of "Operation 100" on 3 May 1939, when airbases of newly-captured territories, specifically in Hubei province including Wuhan, allowed the Japanese to establish airbases and logistics to stage a sustained campaign of massively coordinated joint-strike operations with the Imperial Japanese Navy Air Service heavy bomber units.

[11] U.S. support for China had begun in earnest in 1941 following the Japanese invasion of French Indochina, with the oil and steel embargo against Japan, and consequently, the Japanese raid on Pearl Harbor; beginning in 1942, barrels of 100-octane avgas began to increasingly trickle into China through the cross-Himalayan air-route known as "The Hump" – mostly destined for United States Army Air Force (USAAF) operations – and the Chinese Air Force were provided with new American Republic P-43 Lancer pursuit planes, which in theory with its very fast high-altitude performance and good firepower from its four 50 cal (12.7 mm) M2 Browning machine guns, was quite the upgrade the Chinese Air Force needed to effectively hit back at the Japanese raiders, but it was proven to be extremely unreliable and may have killed more of its own pilots than the enemies, including veteran pilot and 4th PG CO Major Zheng Shaoyu whose P-43 caught fire during a ferrying flight back to combat operations in China and was killed in the ensuing crash.

Zhang tried to save his damaged plane, but it became engulfed by fire, and while bailing-out and parachuting to safety, he was severely burned; he was then attacked by locals who thought he was a Japanese airman as he laid on the ground, barely able to mutter a sound to identify himself, and rescued four hours later, succumbing to his battle wounds the following day in a hospital.

Two months later, after tens of thousands of deaths, in retaliation for firebombing, the United States embargoed the export of airplane parts to Japan, thus imposing its first economic sanction against that nation.

[17] The Japanese air raids against Chongqing had become increasingly intense and destructive as the "joint air strike force" of the Imperial Japanese Army and Navy bomber formations began to comprise upwards of 150–200 bombers per raid, under the new codename "Operation 101" (101号作战), and massed defensive machine gun and cannon fire from the bomber formations were very effective against the slow Chinese fighter aircraft further handicapped with burning low-grade fuel, much of which came by way of French Indochina and processed locally; locally sourced oil came by way of the Yumen Laojunmiao oil wells in Gansu province beginning in the summer of 1939, which produced 90% of the native petrol (250,000 tons) for China during those war years.

The Chinese would be dealt with a serious blow a few weeks later in July 1940 when the British yielded to Japanese diplomatic pressure and closed the Burma Road, which was China's primary lifeline for material and fuel needed in the defense of Chongqing and Chengdu.

[29] On 11 August 1941, in what would be the last-recorded dogfight between the Chinese Air Force fighters and the IJNAF Zeroes before all active Zero squadrons were pulled out of China in preparations for Operation Z (the Pearl Harbor attack mission), future Japanese ace-fighter pilots Gitaro Miyazaki and Saburō Sakai were part of the escort of an Operation 102 bomber attack and fighter sweep of Chinese air bases between Chongqing and Chengdu, and encountered Chinese I-153 and I-16 fighters at Wenjiang Airbase; while shooting down all those that managed to take off or strafing those still taxiing down the runways, Saburo Sakai described how five Zeroes then struggled to shoot down the one last opponent still in the air that "was an absolute master" as it "snap-rolled, spiralled, looped and turned through seemingly impossible maneuvers... like a wraith", but Sakai himself only managed to finally shoot down the acrobatic biplane fighter pilot when he was forced to slow-roll in a climb while trying to clear over the top of a hill west of Chengdu.

The belly of the Chinese fighter suddenly exposed right into the gunsight of Sakai's Zero, who fired cannon shells that "tore through the floorboards of the biplane", sending it down in a wide spin and exploding as it hit the hillside.

On 30 August 1941, Lt. General Saburo Endo, commander of the Imperial Japanese Army's 3rd Sentai, having already received intelligence reports regarding an upcoming military conference in Chongqing held by Generalissimo Chiang Kai-shek, and the precise location for it, led a massive strike from Wuhan consisting of 205 bomber-attack planes, with Saburo Endo himself personally leading the assassination strike on Yunxiu Villa (specifically the Yunxiu Tower); at first, it made a low-level bombing run for accuracy, but was severely hampered by intense bursts of anti-aircraft fire that, according to him, "knocked me up away from my seat several times", and then having to increase altitude to 5,500 meters to make the bombing run instead, killing two guards west of Yunxiu Tower, but failing to kill the Generalissimo, who recorded in his diary how he felt the immense shocks of the bombing and suffering of the people who experienced the torment not just day and night, but for over four years.

Following the Japanese attack on Pearl Harbor in December 1941, the United States declared war on Japan, and President Roosevelt sought an immediate counterattack for the humiliation of Pearl Harbor; in the urgency to keep China resupplied for the new Sino-US joint effort in the war against Japan, General Joseph Stilwell was sent to Generalissimo Chiang Kai-shek on a top secret arrangement for the transfer of North American B-25 Mitchell bomber support equipment, radio-homing navigational aids and 100-octane avgas into China to support the planning of what was to become the Doolittle Raid against the Japanese home islands.

The badly needed high-octane avgas and new equipment in China for the renewed war effort against the Empire of Japan were now increasingly being freighted via the risky Himalayan air-route known as "The Hump".

[citation needed] In March 2006, 40 Chinese who were wounded or lost family members during the bombings sued the Japanese government, demanding 10,000,000 yen (628,973 yuan) each, and asked for apologies.