Allied forces conducted air raids on Japan from 1942 to 1945, causing extensive destruction to the country's cities and killing between 241,000 and 900,000 people. During the first years of the Pacific War these attacks were limited to the Doolittle Raid in April 1942 and small-scale raids on Japanese military positions in the Kuril Islands from mid-1943. Strategic bombing raids began in June 1944 and continued with increasing intensity until the end of the war in August 1945. Allied naval and land-based tactical air units also attacked Japan during 1945.
The United States Army Air Forces (USAAF) campaign against Japan began in earnest in mid-1944. While plans for attacks on the Japanese home islands had been prepared prior to the Pacific War, these could not begin until the long-range Boeing B-29 Superfortress bomber was ready for combat and produced at scale. From June 1944 until January 1945, B-29s stationed in India and staged through bases in China made nine raids on targets in western Japan, but this effort proved ineffective. The strategic bombing campaign was greatly expanded from November 1944, when airfields in the Mariana Islands became available as a result of the Mariana Islands Campaign. Initial attempts to target industrial facilities using high-altitude daylight "precision" bombing were ineffective in significantly degrading Japanese war economy. Much of the Japanese military industry's early-stage manufacturing process was carried out in small, geographically disparate workshops and private homes, reducing the effectiveness of bombing larger factories. Partially in an attempt to address this, beginning February 1945 the USAAF transitioned to a strategy of low-altitude nighttime firebombing against urban areas. This approach caused severe damage to Japan's industrial output, while resulting in widespread urban destruction and high civilian casualties. On 6 and 9 August 1945, the cities of Hiroshima and Nagasaki were mostly destroyed after being struck by American atomic bombs.
Japan's military and civil defenses were ultimately unable to stop or meaningfully hinder Allied air attacks. The number of fighter aircraft and anti-aircraft guns assigned to defensive duties in the home islands was inadequate, and most of these aircraft and guns had difficulty reaching the high altitudes at which B-29s often operated in daytime raids, or operating effectively against them at night. Acute fuel shortages, inadequate pilot training, and a lack of coordination between units also constrained the effectiveness of the fighter force. By June 1945, the Japanese military had decided to cease contesting most Allied air raids, in an effort to stockpile aircraft for defense during the impending invasion of the home islands. Despite the vulnerability of Japanese cities to incendiary bombs, local and municipal firefighting services lacked adequate training and equipment, and few air raid shelters were constructed for civilians. Facing insufficient anti-aircraft defenses, American B-29s were able to inflict severe damage on urban areas, while suffering few losses.
The Allied bombing campaign was one of the main factors that influenced the Japanese government's decision to surrender in mid-August 1945. The morality of large-scale attacks on Japanese cities has been subject to widespread debate, and the American decision to use atomic weapons has been particularly controversial. The most commonly cited estimate of Japanese casualties from the raids is 333,000 killed and 473,000 wounded. Other estimates of total fatalities range from 241,000 to 900,000. In addition to causing extensive loss of civilian life, the raids contributed to a large decline in Japanese industrial production.
Background
United States plans
In 1940, United States Army Air Corps, which was subsumed by the United States Army Air Forces (USAAF) in February 1942, began developing contingency plans for an air campaign against Japan. That same year, the naval attaché to the Embassy of the United States in Tokyo reported that Japan's civil defenses were weak, and proposals were made for American aircrew to volunteer for service with Chinese forces in the Second Sino-Japanese War. The first American Volunteer Group (the "Flying Tigers") began operations as part of the Republic of China Air Force (ROCAF) in late 1941 using P-40 Warhawk fighter aircraft. A second American Volunteer Group was formed in late 1941 and tasked with attacking Japanese targets from bases in China using Hudson and A-20 Havoc medium bombers. The attack on Pearl Harbor on 7 December 1941 led to open hostilities between the United States and Japan and ended the need for covert operations, however, and this unit did not become active. The small number of Second Air Volunteer Group personnel who were dispatched from the United States in November 1941 were diverted to Australia upon the outbreak of war.
Japanese battlefield successes during the opening months of the Pacific War nullified prewar US plans for air raids against the Japanese homeland, and a series of attempts to start a small-scale bombing campaign from bases in China proved unsuccessful. Before the outbreak of war, the USAAF had planned to bomb Japan from Wake Island, Guam, the Philippines and coastal areas in China. However, these areas were rapidly captured by Japanese forces in late 1941 and early 1942, and the USAAF heavy bomber force in the Philippines was largely destroyed when Japanese aircraft attacked Clark Air Base on 8 December 1941.
In March and April 1942, the USAAF attempted to send thirteen heavy bombers to China to attack the Japanese home islands. These aircraft reached India, but remained there as the Japanese conquest of Burma caused logistical problems and Chinese Nationalist leader Chiang Kai-shek was reluctant to allow them to operate from territory under his control. A further thirteen B-24 Liberator heavy bombers were dispatched from the United States to operate from China in May 1942 as the HALPRO force, but were ultimately re-tasked to support Allied operations in the Mediterranean.
In July 1942, the commander of the American Volunteer Group, Colonel Claire Lee Chennault, sought a force of 100 P-47 Thunderbolt fighters and 30 B-25 Mitchell medium bombers, which he believed would be sufficient to "destroy" the Japanese aircraft industry. Three months later, Chennault told United States President Franklin D. Roosevelt that a force of 105 modern fighters and 40 bombers, including twelve heavy bombers, would be able to "accomplish the downfall of Japan" within six to twenty-three months. The USAAF headquarters did not regard these claims as credible, and Chennault's requests for reinforcements were not granted.
Pre-war Japanese defenses
The Japanese government's pre-war air defense strategy to protect the home islands focused on neutralizing enemy air bases. Prior to the war, Japanese strategists believed that Soviet aircraft based in the Russian Far East posed the greatest threat to the Japanese mainland. The Japanese military planned to destroy Soviet air bases within range of the home islands if Japan and the Soviet Union ever went to war. The Soviet Union and Japan only entered hostilities in the final month of the war, by which time Japan lacked the air strength to attack Soviet targets in the Far East.
When the Pacific War began in 1941, the Japanese government believed that the best way to prevent American air raids was to capture and hold the areas in China and the Pacific from which such attacks could be launched. It was expected that the Allies would be unable to re-capture these bases. The Japanese anticipated that the Allies might still make small-scale attacks against the home islands using carrier aircraft. The government chose not to develop strong domestic air defense capabilities, as Japan's industrial resources were unable to maintain offensive air forces in China and the Pacific while also providing an effective defense for the home islands.
Few air units or anti-aircraft batteries were stationed in the home islands during the early months of the Pacific War. In July 1941, the General Defense Command (GDC) was formed to oversee the defense of the home islands. All combat units in this area were assigned to the four regional military districts, the Northern, Eastern, Central and Western districts, which reported directly to the Ministry of War. As a result, the GDC's functions were limited to coordinating communications between the Imperial General Headquarters—Japan's highest military decision-making body—and the military districts.
In early 1942, forces allocated to the defense of Japan comprised 100 Imperial Japanese Army Air Force (IJAAF) and 200 Imperial Japanese Navy (IJN) fighter aircraft, many of which were obsolete, and 500 IJA and 200 IJN anti-aircraft guns. Most of the IJAAF and IJN formations in the home islands were training units with limited ability to counter Allied attacks. The IJA also operated a network of military and civilian observation posts to provide early warning of air attack, and was building a series of radar stations. Command and control of these air defenses was fragmented. The IJAAF and IJN did not coordinate their activities or communicate effectively with each other. As a result, domestic Japanese air defenses were unable to react to a sudden air attack.
Japanese cities were highly vulnerable to damage from firebombing due to their construction, layout and the weak state of Japan's civil defense organizations. Urban areas were typically congested, and most buildings were constructed from highly flammable materials such as paper and wood. Industrial and military facilities in urban areas were often surrounded by densely populated residential buildings. Despite these vulnerabilities, few cities had full-time professional firefighters and relied mostly on volunteers. Professional firefighting forces lacked modern equipment and used outdated tactics. Air raid drills had been held in Tokyo and Osaka since 1928, and from 1937 local governments were required to provide civilians with manuals that explained how to respond to air attacks. Regardless, few air-raid shelters and other air defense facilities for civilians and industry were constructed prior to the Pacific War.
Early raids
Chinese raid
The Republic of China Air Force (ROCAF) conducted a single attack on the Japanese home islands during the Second Sino-Japanese War. On 19 May 1938 two ROCAF Martin B-10 bombers dropped propaganda on Nagasaki, Fukuoka, Kurume, Saga and other locations on Kyushu. These leaflets did not have a meaningful effect on Japanese civilians, but demonstrated that China could potentially conduct small-scale air attacks on Japan. The Japanese military later incorrectly concluded that the ROCAF had aircraft capable of mounting attacks at a range of 1,300 miles (2,100 km) from their bases, and took precautions against potential raids on western Japan when Chinese forces launched an offensive during 1939.
Doolittle Raid
USAAF aircraft bombed Japan for the first time in mid-April 1942. In an operation conducted primarily to raise morale in the United States and to symbolically avenge the attack on Pearl Harbor, sixteen B-25 Mitchell medium bombers were transported from San Francisco to within range of Japan on the aircraft carrier USS Hornet. These aircraft were launched on 18 April, and individually bombed targets in Tokyo, Yokohama, Yokosuka, Nagoya and Kobe. Local Japanese air defense units were taken by surprise, and all the B-25s escaped without serious damage. The aircraft then continued to China and the Soviet Union, though several crashed in Japanese-held territory after running out of fuel. Japanese casualties were 50 killed and over 400 wounded. About 200 houses were also destroyed.
Although the Doolittle Raid caused minimal damage, it had several other important ramifications. The attack raised morale in the United States and its commander, Lieutenant Colonel James H. Doolittle, was seen as a war hero. The weak state of the country's air defenses greatly embarrassed the Japanese military leadership, and four fighter groups were transferred from the Pacific to defend the home islands. Partially in an attempt to prevent further naval air raids, the IJN launched an offensive in the Pacific Ocean which ended in defeat at the Battle of Midway. The Japanese Army also conducted the Zhejiang-Jiangxi campaign to capture the airfields in central China at which the Doolittle Raiders had intended to land. This offensive achieved its objectives and resulted in the deaths of 250,000 Chinese soldiers and civilians; many of these civilian deaths were due to war crimes. The destruction of these airfields and heavy casualties incurred during the fighting badly damaged China's war effort. The IJA also began developing fire balloons capable of carrying incendiary and anti-personnel bombs from Japan to the continental United States.
Bombing of the Kuril Islands
Following the Doolittle Raid, the next air attacks on Japan were made against the Kuril Islands in mid-1943. The liberation of Alaska's Attu Island in May 1943 during the Aleutian Islands campaign provided the USAAF with airfields within range of the Kurils. As part of the preparations for the liberation of Kiska Island in the Aleutians, the Eleventh Air Force conducted a series of raids against the Kurils to suppress Japanese air units stationed there. The first of these attacks was made against southern Shumshu and northern Paramushiru by eight B-25s on 10 July. The Kurils were attacked again on 18 July by six B-24 Liberator heavy bombers, and the unopposed liberation of Kiska (Operation Cottage) took place on 15 August.
The Eleventh Air Force and U.S. Navy units continued to make small-scale raids on the Kuril Islands until the closing months of the war. The USAAF attacks were broken off for five months following a raid on 11 September 1943 when nine of the twenty B-24s and B-25s dispatched were lost, but raids by US Navy PBY Catalinas continued. In response to the American attacks, the IJN established the North-East Area Fleet in August 1943, and in November that year Japanese fighter strength in the Kurils and Hokkaidō peaked at 260 aircraft. The Eleventh Air Force resumed offensive operations in February 1944 after it had been reinforced with two squadrons of P-38 Lightning escort fighters, and it continued to attack targets in the Kurils until June 1945. While these raids caused little damage, they caused the Japanese to divert large numbers of aircraft and other military assets to defend their northern islands against a potential United States invasion.
Operation Matterhorn
Preparations
In late 1943, the United States Joint Chiefs of Staff approved a proposal to begin the strategic air campaign against the Japanese home islands and East Asia by basing B-29 Superfortress heavy bombers in India and establishing forward airfields in China. This strategy, designated Operation Matterhorn, involved the construction of large airstrips near Chengdu in inland China which would be used to refuel B-29s traveling from bases in Bengal en route to targets in Japan. Chennault, by now the commander of the Fourteenth Air Force in China, advocated building the B-29 bases near Guilin, closer to Japan, but this area was judged too vulnerable to counterattack. However, the decision to build airstrips at Chengdu meant that Kyūshū was the only part of the home island chain within the B-29's 1,600-mile (2,600 km) combat radius. Construction of the airfields began in January 1944, and the project involved around 300,000 conscripted Chinese labourers and 75,000 contracted workers.