The bombing of Chongqing (simplified Chinese: 重庆大轰炸; traditional Chinese: 重慶大轟炸, Japanese: 重慶爆撃), from 18 February 1938 to 19 December 1944, was a series of massive terror bombing operations authorized by the Empire of Japan's Imperial General Headquarters and conducted by the Imperial Japanese Army Air Service (IJAAF) and Imperial Japanese Navy Air Service (IJNAF). 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.
According to incomplete statistics, a total of 268 air raids were conducted against Chongqing, involving anywhere from a few dozen to over 150 bombers per raid. These bombings were probably aimed at cowing the Chinese government, or as part of the proposed Japanese invasion of Sichuan which ultimately never occurred.
Opposing forces
China
The centralized command of the Republic of China Air Force integrated many former Chinese warlord air force aircraft and crews, and numerous Chinese-American and other foreign aviators volunteering for service with the Chinese Air Force. Nominally referred to as the Nationalist Air Force of China, at the outbreak of the air war in 1937 it was equipped mainly with US-made aircraft and training, as well as aircraft and training from other foreign sources, including Italian and Japanese army air force instructors. China was not an aviation industrial power at the time, and by the end of 1938 had suffered severe losses through attrition at the Battle of Shanghai, the Fall of Nanjing, the Fall of Taiyuan, and the Fall of Wuhan. The Chinese had found new hope in the lifeline of the Sino-Soviet Non-Aggression Pact of 1937, and Chinese Air Force pilots had almost completely transitioned into the Soviet-made Polikarpov I-15 and I-16 series of fighter-pursuit aircraft by early 1938. Along with a few remaining Curtiss Hawk IIIs which were China's frontline fighter-attack weapon of choice at the beginning of War of Resistance-World War II in 1937. A handful of other fighter-aircraft models were also available to the Chinese, including several Dewoitine D.510 fighters left by the defunct French Volunteer Group (the 41st PS), which was disbanded in October 1938 due to difficulties in combating the Mitsubishi A5M fighter. 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. Consequently, 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.
Primary and auxiliary airbases used by the Chinese Air Force in the Chongqing and Chengdu defense sector included Baishiyi Airbase, Fenghuangshan, Guangyangba, Liangshan, Shuangliu, Suining, Taipingsi, Wenjiang, and Xinjin, among others. There were 18 primary anti-aircraft artillery batteries positioned around Chongqing from 1939 to 1942, not including the air force's anti-aircraft gun units assigned specifically for the defense of the airbases.
As the Chinese government and military forces fell-back and engaged the Japanese advances in new frontline operations in the beginning of 1938 at Wuhan, Taierzhuang, Guangdong and other main battle lines, the Imperial Japanese Army Air Force began harassing the deep-rear with exploratory strikes against the anticipated national fortress of Chongqing, while the Imperial Japanese Navy Air Force was hitting hard at the main battle-front of the temporary wartime-capital Wuhan. 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. The introduction of the Mitsubishi A6M Zero fighter in 1940, the most advanced fighter aircraft produced at the time, ensured the Japanese practically complete air supremacy. 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.
Chongqing's mountainous topography provided significant opportunities for building air-raid shelters, although digging them required difficult manual labor. Critical infrastructure was protected underground, including factories, government facilities, and Chongqing's radio station.
Japan
The majority of the Japanese air raids conducted against Chongqing and other targets around Sichuan were made with squadrons of medium-heavy bombers composed of IJNAF Mitsubishi G3M variants, known under Allied codename "Nell" and the IJAAF Mitsubishi Ki-21 "Sally"; others include the Fiat BR.20 Cicognas ("Ruth"), Kawasaki Ki-48 "Lily", and Nakajima B5N "Kate". Prior to the departure of the crack Japanese naval air units in China for the Pacific War in mid-late 1941, the new successor to the G3M bomber, the Mitsubishi G4M "Betty" and the Aichi D3A dive-bomber were operationally tested in the bombing of Chongqing, followed by newer designs such as the Mitsubishi Ki-67 "Peggy", Nakajima Ki-49 "Helen", and Yokosuka P1Y "Frances" (successor to the G4M), which were deployed in the following years as the bombing of Chongqing continued.
Raids
In the first two days of the Operation 100 (100号作战) bombing campaign, 54 and 27 Japanese bombers raided Chongqing on 3 and 4 May 1939 respectively, dropping approximately a 3:2 ratio of Type 98/25 high explosive "land bombs" (98 dropped on day one) and Type 98/7 incendiary bombs (68 dropped on day one). The first raid killed almost 700 residents and injured 350 more. Major Deng Mingde led the 22nd Pursuit Squadron (of the 4th Pursuit Group) Polikarpov fighters against the bombers on 3 May, shooting down seven bombers but losing two pilots including his deputy commander, the veteran Zhang Mingsheng. 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.
The pre-dawn attack on 4 May resulted in far more casualties, with over three thousand deaths, injuring almost 2,000 more, and leaving about 200,000 homeless. Although the attacking force was smaller and dropped fewer bombs, there was no interception of the bombers by the Chinese Air Force whose airbases in the Chongqing region were not yet set up for nighttime operations.
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.
The Japanese began to embark more nighttime bombing raids against Chongqing in summer of 1939 in an effort to reduce confrontation and casualties from defending Chinese Air Force fighters; however, the Chinese pilots began operating nighttime interceptions over Chongqing with some success in shooting down the nighttime bombers using "lone wolf" fighter tactics previously deployed during the Battle of Nanking two years earlier (and similar to the Wilde Sau tactics the Luftwaffe would deploy a few years later). The interceptions involved the coordination with a series of manually operated ground-based searchlights illuminating and tracking incoming bombers which can then be seen and targeted by the solitary fighter pilot; fighter ace Liu Zhesheng shot down a bomber on the night of 3 August 1939 flying "lone wolf" in an I-15bis during such a nighttime interception mission over Chongqing, among several other kills he claimed while battling for the defense of Chongqing. In the following night, Capt. Cen Zeliu would also claim a nighttime kill of a bomber while at the controls of an I-15bis.
"The Japanese bombers appeared over Chungking on moon-lit nights when they could easily see the major landmarks... from time to time, on command of their formation leader, all the bombers would open up a defensive barrage of fire in direction most likely of attack by fighters. The performance was effective. It was like a gigantic broom of fire sweeping the starry sky."
— K. Kokkinaki, Soviet pilot, witnessing the spectacle of night-time air-raids over Chongqing in 1939
Monks of the Ciyun Temple contributed greatly to rescuing and saving lives of residents over the course of the half-decade-long bombing campaigns over Chongqing.
Some foreign journalists and diplomats who witnessed the bombing of Chongqing described it as "China's apocalypse".
By mid-1940, the IJNAF G3M Model 21 bombers that formed the primary aircraft of the carpet-bombing campaign against Chongqing and Chengdu had become largely relegated to nighttime bombing attacks, while daylight raids were being replaced with the new and improved Model 22/23 G3Ms equipped with the higher-octane rated and supercharged Kinsei 51 engines, boosting the power of each of the twin-engined bombers by 500 horsepower and greatly enabling the schnellbomber strategy further above the general obsolescence of the defending Chinese fighter aircraft now struggling to gain speed and altitude to make even a single head-on pass against the high-speed/high-altitude IJNAF bombing runs, and even more vulnerable to the massed-firepower of those heavy bomber formations.
Also by mid-1940, the Japanese had employed new tactics to stave off attacks from defending Chinese fighters; the Chinese air raid early warning network would alert the Chinese fighter squadrons to scramble their fighters toward approaching Japanese bomber formations (ideally with ample time to attain sufficient altitude ahead of the raids); however, they were being monitored by fast IJNAF C5M (IJAAF designation Ki-15) scouting-attack planes at high altitudes which would radio instructions to the bombers to circle out of range as the Chinese fighters rose to meet the bombers; once the Chinese fighters had run low on fuel and returned to base, the scouts would then redirect the bombers to attack the Chinese fighters on the ground refueling. While the Chinese soon cracked the code used by the C5M crews relaying messages to the bomber formations, some of the countermeasures used by the Chinese pilots were to launch a pair of I-16s that were almost fast enough to intercept the C5M in pursuit, but enough to force the scouts away, while a second flight of fighters were launched against returning Japanese bombers as the first flight of Chinese interceptors returned to disperse in smaller auxiliary airbases to refuel, although successful interceptions were still limited against the IJNAF bombers as the Polikarpovs struggled in particular against the new Model 22/23 G3M bombers.