The United States Army Air Forces launched a bombing raid on Tokyo and other Japanese cities on April 18, 1942, during World War II. Using the aircraft carrier Hornet, Lieutenant Colonel James H. Doolittle led sixteen B-25 bombers in a daring surprise attack that did relatively little damage but improved Allied morale. As a result of the attack, Japan kept four army fighter groups at home in 1942 and 1943, when they were desperately needed in the South Pacific theater of operations. The Japanese were forced to extend their defensive perimeter beyond their initial plans, which left their supply routes exposed.

The beginning of 1942 was a dismal period for the Allies. The United States' war machine had not yet been completely organized after Pearl Harbor. In North Africa, Erwin Rommel's Afrika Korps was wreaking havoc, and in Britain, the Luftwaffe was waging a relentless bombing campaign on the country's major towns. After the Red Army and a harsh Russian winter just outside of Moscow had stopped the German offensive on the Eastern Front, they were prepared to resume it in the summer. The Allies were on the losing end of the Battle of the Atlantic, and the success German U-boat captains were having against Allied commerce earned them the moniker "the second happy time." Japan's military had won a streak of victories that seemed to go on forever, and the country's sphere of influence had grown to encompass places like the Philippines, Hong Kong, Singapore, Indonesia, and Malaysia. The Japanese had scored a Pyrrhic triumph at Wake Island, and the valiant but ultimately futile resistance of Bataan by Filipino and American forces was the only bright spot in an otherwise dismal Pacific theater. In the immediate aftermath of Pearl Harbor, U.S. President Franklin D. Roosevelt tasked his military leaders with carrying out a strike on Japan that would bolster American morale. These were critical days, dominated by holding actions and desperate defensive plans. While the scale of the U.S. response was obviously reduced by the destruction done to the Pacific Fleet at Pearl Harbor, American planners still thought of an aggressive assault against the core of the Japanese empire. The United States would launch a direct air strike on Tokyo. The primary goals of the raid would be to cause material damage by destroying military targets, which would slow down Japanese war production, and to instill fear in the Japanese populace, which would force military leaders to recall combat equipment from other theaters for home defense. The burden on other Allied forces in the Pacific would be lightened as a result of this. It was believed that the raid would do more than just distract the American people from the constant stream of awful news coming from the front lines; it would also demonstrate American resolve to the other Allied forces.

U.S. Navy Capt. Francis S. Low proposed the idea of launching U.S. Army Air Forces bombers from the deck of an aircraft carrier to Adm. Ernest King in January 1942. With Arnold's blessing, "Special Aviation Project No. 1" expanded to include both the Army and the Navy. When Doolittle and Low successfully launched two B-25 Mitchell bombers from the deck of the USS Hornet on February 3, 1942, they proved the strategy could work. After dropping their bombs, the planes would make a beeline for Vladivostok, Russia, or an empty part of China. The talks with the Soviets regarding landing on their territory failed. The B-25s had their weight reduced and their range increased because of these modifications. The defensive turret was removed, but a "tail gun" made of painted broomsticks was installed as a makeshift replacement. Each plane was loaded with either incendiary or high-explosive bombs weighing two thousand pounds, and the mission was conducted at dangerously low altitudes. Captain C. Ross Greening came up with a simpler alternative to the cumbersome Norden bomb sight, dubbing it the "20-cent sight" because of its low cost. For this mission, saving gasoline was more critical than pinpoint bombardment. The 17th Bombardment Group embarked on a three-week mission training program at Eglin Field in Valparaiso, Florida. Cross-country flight, night flying, low-altitude bombing, and navigational training were all provided to pilots and navigators. The gunners were given basic instruction on how to use their equipment. On April 1, 1942, at Naval Air Station Alameda, 16 modified B-25s were hoisted onto the flight deck of the Hornet, and the next day, under the cover of a heavy fog, the carrier proceeded out of San Francisco Bay. Collectively, the flotilla was referred to as Task Force 18. Before heading to the launch point 400 miles (640 km) off the coast of Japan, the USS Hornet had to meet up with the carrier USS Enterprise and William "Bull" Halsey's Task Force 16. The Hornet's flight deck was crowded with B-25s belonging to the raiders; thus, the Enterprise's planes were responsible for aerial patrol and reconnaissance. Gunners aboard the Hornet continued their training as usual, this time utilizing kites as targets for their turret exercise. However, the approach was spread out along a front of 50 miles (80 kilometers), so each flight of three planes had its own unique trajectory. Lieut. Travis Hoover's flight was tasked with attacking northern Tokyo; Captain David M. Jones's flight was responsible for central Tokyo; Captain Edwin J. York's flight was tasked with attacking southern Tokyo and the north-central part of Tokyo Bay; and Captain C. Ross Greening's flight was tasked with attacking Y. The raiders' first plan called for them to take off several hours before daylight, but this was scrapped after discussions with the Navy. A second strategy involved taking off before sunrise, bombing in the early morning, and landing in China before nightfall. The B-25s were to take out at night, bomb their targets, and then fly to unoccupied Chuchow (Quzhou) in China the following morning. Doolittle's plane was supposed to take off first, drop incendiary bombs on military targets in central Tokyo, and light the way for the rest of the raiders. But the military adage that "no plan survives contact with the enemy" was proven true once again.

On April 18 at 3:10 AM, the Enterprise's American radar operators picked up a Japanese picket boat well outside the patrol area. As more and more Japanese ships showed up on the radar, the task force adjusted its route. At 7:38 a.m., Hornet lookouts sighted a Japanese patrol boat only 18,000 miles (20,000 meters) from the carrier. Despite the fact that the USS Nashville rapidly sank the ship, a transmission was received in the Hornet's radio room warning the Japanese troops of the Americans' presence. Doolittle wanted to launch his planes from a range of 640 to 965 kilometers away from their intended objective, but Halsey was unwilling to risk his precious carriers by approaching the Japanese defenses any closer. Halsey radioed the launch plans to the Hornet. "GOD BLESS YOU AND THE GALLANT COMMAND, COL. DOOLITTLE AND THE GALLANT COMMAND" At the same moment, Halsey sent his own planes into the air to attack the Japanese ships. More than 1,320 kilometers (or more than 820 miles) separated the Hornet and Tokyo at this time. The flight crews were given their final orders, which included a strict prohibition on targeting civilian areas such as the Imperial Palace complex in central Tokyo (which the United States would later firebomb to nearly complete destruction in May 1945). Pilots were told to fly as far west as they could, abandon their planes at sea, and swim or paddle to shore if they were unable to reach the Chinese coast. They were not to divert to the Soviet Union. For most of the planes, this wasn't necessary because a 25-mile-per-hour (40-kilometer-per-hour) tailwind helped them cover the final 1,200 miles (1,900 km) of the trip. Doolittle's B-25 was the first to take off from the deck of the Hornet at 8:20 a.m. after the personnel had boarded their aircraft following the final briefing. Within an hour, all of the invaders had successfully taken off into the sky, despite the rough waves. The journey to the target went off without a hitch. The raiders encountered a multi-engine land-based jet an hour into the trip, and an hour later, they saw a ship they believed to be a camouflaged light cruiser. From then on, they did their best to stay out of sight of the numerous civilian and military vessels that began to appear on the ocean. A landing was made a short distance off track, to the north of Cape Inub. Doolittle's group came upon Tokyo from the north, while the other flights followed orders. As low as the terrain would allow, the raiders looked up to see a fleet of small biplanes, perhaps trainers. About nine Japanese fighters (in three flights of three planes) were detected roughly 10 miles (16 km) north of Tokyo, but they did not initiate combat with the B-25s. The raiders flew at an altitude of 1,200 feet (366 meters) as they closed in on their objectives. They dropped their bombs, retreated to flying above the treetops, and headed west over the city's outskirts. During the operation, aviation pilots allegedly dropped 14 tons of bombs on the Japanese mainland and claimed to have struck nearly all of their principal objectives. Large fires were reportedly seen from several of the planes as a consequence of incendiary bombs, while factories, ammo depots, naval installations, and military barracks were visibly damaged by high-explosive ordnance. Crews reported heavy but inaccurate antiaircraft fire after the operation. The Japanese gunners had good altitude judgment, but their bursts missed the planes entirely to the right or left, so the raiders suffered no casualties from flak.

Most of the raiders set sail for the China coast from the south after departing Tokyo. The weather over the East China Sea turned terrible, even if it was clear above Japan. In an effort to fly above the storm, the pilots increased their height, and by the time they reached the Chinese coast, they were 6,000 feet (1.8 km) in the air. The visibility was so low that the raiders had to rely only on their instruments. Doolittle, whose plane still had a working command radio, tried to contact Chuchow but got no answer. He ordered the evacuation of his crew when gasoline ran low. Doolittle followed after setting the plane on autopilot, but not before checking the time: it was 9:20 p.m., 13 hours to the minute after he had taken off from the Hornet. Doolittle's jet made a safe landing on Chinese territory, and he and his crew were able to get in touch with the local authorities right away. Doolittle requested that the director of the branch government in western Chekiang (Zhejiang) province, General Ho Yang Ling (He Yangling), keep watch along the coast for any downed aircraft or boats that might have made it ashore. After a few days on the road, Doolittle's crew made it to Chungking (Chongqing). Doolittle wired Arnold from the American embassy in Chungking at dawn on April 20 to report that they had successfully bombed Tokyo with four extra planes and personnel. It is assumed that all Chinese aircraft crashed on the coast due to the storm. So far, China has accounted for five complete crews. Corporal Leland Faktor, Sergeant William Dieter, and Corporal Donald Fitzmaurice were the three members of crews that made it to China who were killed in mishaps involving bailouts or crash landings. Of the 16 crews, just three didn't make it to Chungking. Captain Edwin J. York, who was in charge of the third group of planes to arrive in Tokyo, ran out of fuel and had to make an emergency landing near Vladivostok. After spending almost a year in Soviet detention facilities, he and his team "escaped" into British and Soviet-occupied Iran. Their "escape" was a complex NKVD operation designed to return the Americans to the United States while offering the Soviets plausible deniability with the Japanese, who were still on friendly terms at the time. After ejecting over China, two crews were captured by Japanese forces, one near the coast and the other near Lake Poyang. The Chinese made fruitless attempts to buy the freedom of the captured flight men. The Japanese held four of the raiders hostage until the war's conclusion. One of them, Lieutenant Robert J. Meder, passed away in 1943 from dysentery. In October 1942, the Japanese hanged Lieutenant Dean Hallmark, Lieutenant William Farrow, and Sergeant Harold Spatz. Although the bombing caused relatively minor material destruction, it had a profound emotional impact on both the United States and Japan. Doolittle was given the Congressional Medal of Honor and appointed brigadier general after the operation, and the Army Air Forces utilized it as a recruiting tool. Thirty Seconds Above Tokyo (1943), written by pilot Captain Ted W. Lawson, became a best-seller and was later turned into a film starring Spencer Tracy as Doolittle. The presence of American bombers over Tokyo prompted the Japanese to hasten the building of their defensive perimeter, despite the fact that they had not previously considered the likelihood of an attack on their home islands. The invasion of the Midway Islands in the Pacific would be the climax of these events. Adm. Chester Nimitz, commander of the Pacific Fleet, received orders to intercept the Japanese naval force when U.S. cryptanalysts cracked the Japanese JN25 naval code. U.S. naval air power then destroyed Japan's first-line carrier strength at the Battle of Midway (June 3-6, 1942), which turned the course of the Pacific War. The Japanese army was conducting a horrific campaign of reprisals in southeastern China while the navy was fighting for its own existence. Even though the Second Sino-Japanese War had stalled by 1942, the Doolittle Raid brought attention to the danger presented by airfields in Nationalist-controlled areas along the Chinese coast. Japanese strategists quickly began plotting a campaign to deactivate the airfields and punish anyone who had helped the Americans in the days following the raid. A Japanese drive into Chekiang and Kiangsi (Jiangxi) began in early June 1942, and the cruelty directed at the local civilian population evoked memories of the Nanjing Massacre. Villages were destroyed because appreciative Americans left trinkets and keepsakes behind, including parachutes, cigarettes, and pieces of military equipment. The provincial capital of Kiangsi, Nancheng (Nanchang), was obliterated and its population wiped out by Japanese bombing raids. During the three-month retaliation campaign, an estimated 250,000 civilians were slaughtered. Unit 731 of the Japanese military's famed germ warfare program moved into Chekiang and Kiangsi as the army was about to evacuate. Those who had survived the early Japanese attacks were decimated by dysentery, typhoid, and cholera that had been planted in the area. A museum honoring the Chuchow (Quzhou) locals who helped American air crews during the Doolittle Raid opened in 2018.