The raid had its start in a desire by President Franklin D. Roosevelt, expressed to Joint Chiefs of Staff in a meeting at the White House on 21 December, 1941, that Japan be bombed as soon as possible to boost public morale after the disaster at Pearl Harbor.
The concept for the attack came from Navy Captain Francis Low, Assistant Chief of Staff for Anti-submarine Warfare, who reported to Admiral Ernest J. King on 10 January 1942, that he thought that twin-engined Army bombers could be successfully launched from an aircraft carrier after observing several at a naval airfield in Norfolk, Virginia, where the runway was painted with the outline of a carrier deck for landing practice. It was subsequently planned and led by Doolittle, a famous civilian aviator and aeronautical engineer before the war.
Requirements for the aircraft for a cruising range of 2,400 miles (3,900 km) with a 2,000 pound (900 kg) bomb load resulted in the selection of the North American B-25B Mitchell to carry out the mission. The B-26 Marauder, B-18 Bolo, and B-23 Dragon were also considered, but the B-26 had questionable takeoff characteristics from a carrier deck, and the B-23's wingspan was nearly 50% greater than the B-25's, reducing the number that could be taken aboard a carrier and posing risks to the ship's island. The B-18, one of the final two types considered by Doolittle, was rejected for the same reason.
Subsequent tests with B-25s indicated they could fulfill the mission's requirements. Doolittle's first report on the plan suggested that the bombers might land in Vladivostok, shortening the flight by 600 miles (1,000 km), on the basis of turning over the B-25s as Lend-Lease. However, negotiations with the Soviet Union (which was not at war with Japan) for permission were fruitless.
 TrainingLt. Col. Doolittle wires a Japanese medal to a bomb, for "return" to its originators.
When planning indicated that the B-25 was the aircraft best meeting all specifications of the mission, two were loaded aboard the aircraft carrier USS Hornet at Norfolk, Virginia, and subsequently flown off the deck without difficulty on 3 February 1942. The raid was immediately approved and the 17th Bomb Group (Medium) chosen to provide the pool of crews from which volunteers would be recruited. The 17th BG had been the first group to receive B-25s, with all four of its squadrons equipped with the bomber by September 1941. The 17th not only was the first medium bomb group of the Army Air Corps, but in the spring of 1942, also had the most experienced B-25 crews. Its first assignment following the entry of the United States into the war was to the U.S. Eighth Air Force.
The 17th BG, then flying antisubmarine patrols from Pendleton, Oregon, was immediately moved cross-country to Lexington County Army Air Base, Columbia, South Carolina, ostensibly to fly similar patrols off the east coast of the United States, but in actuality to prepare for the mission against Japan. The group officially transferred to Columbia effective 9 February, where its combat crews were offered the opportunity to volunteer for an "extremely hazardous" but unspecified mission. On 17 February the group was detached from the Eighth Air Force.
Initial planning called for 20 aircraft to fly the mission, and 24 of the group's B-25B Mitchell bombers were diverted to the Mid-Continent Airlines modification center in Minneapolis, Minnesota. Modifications included:
Two bombers also had cameras mounted to record the results of bombing.
The 24 crews selected picked up the modified bombers in Minneapolis and flew them to Eglin Field, Florida, beginning 1 March 1942. There the crews received intensive training for three weeks in simulated carrier deck takeoffs, low-level and night flying, low-altitude bombing, and over-water navigation. Navy Lt. Henry Miller supervised their takeoff training and accompanied the crews to the launch. For his efforts, Lt. Miller is considered an honorary member of the Raider group. Lt. Col Doolittle stated in his after action report that an operational level of training was reached despite several days when flying was not possible because of rain and fog. One aircraft was heavily damaged in a takeoff accident and another taken off the mission because of a nose wheel shimmy that could not be repaired quickly enough.
On 25 March, the remaining 22 B-25s took off from Eglin for McClellan Field, California. They arrived on 27 March for final modifications at the Sacramento Air Depot. A total of 16 B-25s were subsequently flown to Alameda, California, on 31 March. Fifteen raiders would be the mission force and a 16th aircraft, by last minute agreement with the Navy, would be squeezed onto the deck to be flown off shortly after departure from San Francisco to provide feedback to the Army pilots about takeoff characteristics. (The 16th bomber was made part of the mission force instead.)