The nuclear element of the bomb came into the hands of the 393rd Bombardment Squadron, the business end of the 509th Composite Group, which included support personnel for the 393rd’s pilots. The 509th had been constituted the previous October at Wendover Field, Utah, on the edge of the great salt flats that had long discouraged travelers to the American west but now provided a practice range for the unit’s fliers. The group was commanded by Paul W. Tibbets, a 29-year-old lieutenant colonel who had extensive experience as a bomber pilot in Europe. When given his command, Tibbets had been told about the Manhattan Project, the offspring ofwhich might win the war. He would be given the best pilots and crews, the new, state-of-the-art B-29 bomber (which would arrive in Utah that December), and access to whatever resources he needed to make his group work, though he was not to tell his men what kind of weapon they would be carrying. Tibbets would build the 509th to a strength of 1,800, 117 of whom were formed into thirteen B-29 crews and trained, unwittingly, to drop atomic bombs. They practiced over Utah, Nevada, and California through the winter of 1944-5. In clear daylight, they flew to 30,000 feet, took aim at circular targets inscribed for them on the desert floor or at a white raft in California’s Salton Sea, and released monstrously heavy bombs made of concrete and with high explosives lodged in their noses. These were painted orange and thus christened ‘pumpkins’. Tibbets instructed his men to turn sharply, at 155 degrees, just after they had released their pumpkins, and to fly away quickly once they had made their drops. In their off hours men blew off steam over the border in Nevada casinos, but they were closely monitored by security police. No one was to talk about what they were doing or the size or shape of the pumpkins. Transgressors were banished to a base in the Aleutian Islands for the rest of the war.17
Through the spring, as firebombs devastated Tokyo and officials chose other Japanese cities to be spared temporarily for subsequent atomic bombings, Tibbets continued to drill his fliers. He sent a group to Batista Field in Cuba, whence they practiced carrying heavy loads for distance over water, dropping 10,000-pound bombs accurately from high altitude, then returning to base with a limited supply of fuel. Tinian’s airbase, already home to B-29s flying missions over Japan, began receiving elements of the 509th late in the spring; Tibbets and his pilots and crews arrived on 15 June. There they practiced some more, dropping pumpkins on Japanese targets in the Marianas and Carolines through mid-July, then dropping the bombs on cities in Japan starting on the 19th. Curtis LeMay himself approved each mission; Tibbets was withheld from all of them. (The 393rd ultimately conducted thirteen pumpkin attacks on Japan, with the final mission numbered 14, reserving lucky 13 for Hiroshima.) Command hoped not only to prepare its crews for the a-bomb runs, but to lull the Japanese into thinking that attacks by single B-29s failed to amount to much and were hardly worth opposing. ‘The pumpkins were respectable bombs,’ recalled an engineer for the 509th, though not worth Japan’s trouble of sending up scarce fighter planes or even sounding citywide alarms. Apart from these raids, 509th crews appeared mostly to sit in their mysteriously well-guarded compound while men in other units took on duties far more frequently and at greater risk. The 509th huts were thus on the receiving end of rocks tossed resentfully over the barbed-wire perimeter. The men grinned and bore it and even named their well-used movie theater ‘The Pumpkin Playhouse’. They still did not know why they were there.18
They finished assembling Little Boy on the last day of July. Brigadier General Thomas Farrell, on Tinian as Groves’s deputy, wired his boss that the bomb could be dropped as early as the next day. But the weather looked bad, and there was a bit more to do. On 2 August, Tibbets, with his bombardier Thomas Ferebee, met LeMay at the general’s headquarters on Guam. LeMay confirmed what they had long discussed: Little Boy’s target was Hiroshima, a southern port city on Japan’s Inland Sea. LeMay had a recent reconnaissance map of the city, and he asked Ferebee to choose an aiming point. Ferebee quickly spotted the Aioi Bridge, a distinctive T-shaped structure that spanned the (Ota River close to the center of the city; the others approved. Seven B-29s would take part in the mission: three would fly ahead, over Hiroshima and the alternative targets of Kokura and Nagasaki (the latter a fresh addition to the targets’ list), to check on the weather; another would be flown to Iwo Jima, where it would serve as a backup carrier for Little Boy if something went wrong with the bomb-bearing plane in flight; and two more—Charles Sweeney’s Great Artiste and George Marquardt’s prosaically named No. 91—would accompany the atomic bomber, carrying blast measurement instruments and cameras respectively. The seventh B-29 would be piloted by Tibbets himself. It had never been named.
Back on Tinian on Saturday 4 August, Tibbets summoned the crews of the mission bombers to the unit’s briefing hut. He had two officers pull aside drapes to reveal blackboard-mounted maps of the three target cities. He then stepped aside for William ‘Deke’ Parsons, head of the Manhattan Project’s Ordnance Division, who was instrumental in developing the uranium gun at the heart of Little Boy and who would arm the bomb on mission day and fly with Tibbets. Parsons had brought with him a film clip of the Trinity test and started to screen it for the men, but the projector jammed irretrievably—whereupon Parsons described the blast from memory. He never used the words ‘atomic’ or ‘nuclear’, but he warned the pilots against straying too close to the mushroom cloud the anticipated explosion would generate. They could not know for certain what would happen, Parsons concluded, but the consequences of a successful drop were likely to be enormous. Tibbets then finished the session with reminders about routes and timings and reassurances concerning rescue should any of the planes be forced down over water. He told the crewmen not to say anything about the mission, in letters home or on base. He ended with a pep talk—and the declaration that the bomb ‘would shorten the war by at least six months’. Thus sobered, and encouraged, the men shuffled off to contemplate their course. Tibbets then took his crew for a final rehearsal over Tinian. He flew straight and level and Ferebee released a pumpkin over the sea. It all checked out.