Japanese Prime Minister Baron Kantaro Suzuki, whose Cabinet was divided on whether to fight on, replied to the declaration using the word mokusatsu . The Americans interpreted this as "to ignore." But it could have also been read as "no comment," which might have hinted at a more compliant response.
But by then the components of Little Boy, a gun-type bomb using Uranium 235, had already arrived at Tinian, the vast B-29 base 1,200 miles south of Tokyo.
Since its capture in 1944, Tinian had become a mammoth fixed aircraft carrier. Its six 10-lane runways could launch a B-29 every 15 seconds. The 509th settled in, surrounded by an air of mystery.
Tail gunner Sgt. Robert Caron of Tibbets' crew amused himself by stealing lumber from the Officers' Club to make a porch for his Quonset hut. Flight Engineer Sgt. Wyatt Duzenbury hunted Japanese at night, looking for souvenirs. Navigator Capt. Theodore Van Kirk and Maj. Thomas Ferebee, the bombardier, played poker when not dropping last-minute "pumpkins" into the Pacific.
The Target Committee, headed by Maj. Gen. Leslie Groves, who had directed the Manhattan Project that created the bomb, had drawn up a list of cities. The criteria were that it be a military and-or industrial city and one unscathed by bombing so that the effects of a nuclear explosion could be evaluated.
The problem was that much of Japanese manufacturing was scattered piecemeal through residential areas.
The amount of lethal radiation from a bomb was an uncertain quantity to scientists, but the bomb was to go off at 1,850 feet, so, it was believed, it would kill by blast, not rays.
J. Robert Oppenheimer, director of the Los Alamos facility that designed the weapon, figured on 20,000 killed, assuming the populace was in shelters.
Hiroshima, a military town of 280,000 civilians and 43,000 soldiers--and 23 American POWs in the city's castle--had been hit by two bombs from four carrier planes and once by a single B-29. Four people were killed.
LeMay had intentionally left it unscathed. It was target No. 1, with Niigata and Kokura Arsenal alternates if Hiroshima was unfeasible because of weather. (The bombing would have to be visual, not by radar, to assess the results. On Aug. 4, Nagasaki was subbed for Niigata due to weather.)
The next day, Tibbets summoned the base sign painter from a softball game to paint his mother's name on B-29 No. 82.
Little Boy was gingerly winched into the bomb bay. It was 10-feet, 6-inches long, 29 inches in diameter and 9,700 pounds, about 92 pounds of it U-235 produced in ounces per day at Oak Ridge, Tenn.
Capt. William Parsons, a Navy ordnance expert, had decided to arm the bomb in flight lest it explode in a takeoff crash.
Each man was issued a cyanide capsule. Radar Specialist Lt. Jacob Beser--Little Boy's trigger was set off by radar transmitters geared to precise altitude--was given the frequencies on rice paper so he could eat them if facing capture.
"All set, Dooz?" Tibbets asked his 32-year-old flight engineer, a one-time tree surgeon who thought the cargo looked like a tree trunk.
"All set, colonel."
"Dimples eight-two from north Tinian tower," radioed the traffic controller. "Take off to the east on Runway A for Able."
At 2:45 a.m. on Aug. 6, 1945, Tibbets gunned his overloaded bomber.
"I never saw a plane use that much runway," said Brig. Gen. Thomas F. Farrell, Groves' deputy on the island. "I thought Tibbets was never going to pull it off."
In his tail cubbyhole, gunner Caron in his Brooklyn Dodgers baseball cap asked: "Colonel, are we carrying a chemist's nightmare?"
"Not exactly," Tibbets replied.
"How about a physicist's nightmare?" he asked, taking a wild guess.
"He gave me a really funny look," Caron recalled, and said: 'That's about it.' "
Seven B-29s in all made up Operation Centerboard. One was standing by on Iwo Jima, an island captured in February at the cost of almost 6,000 Marine lives, in case Enola Gay broke down. Over Iwo Jima, Tibbets formed into a V as two observer and instrument bombers joined him. Up ahead, three weather planes scouted the targets.
One of the observers was Harold Agnew, a physicist at Los Alamos. He was the only one who also had been present at Enrico Fermi's historic squash court in Chicago in 1942, when man's first controlled nuclear reaction produced about enough energy to light a cigarette.
He had come full circle, from spark to bomb.
"I had lost a lot of friends in the Pacific war," Agnew said. "Some New Mexico National Guardsmen had been on the Bataan Death March. I had a chip on my shoulder."
Cruising at 205 knots, Tibbets got the weather report for Hiroshima: A 10-mile hole in the clouds over the city. "Advice: Bomb primary."
Tibbets began climbing. At 31,600 feet, he turned to 264 degrees and slowed to 200 knots. Ahead, clearly visible, was the T-shaped Aioi Bridge, Ferebee's aiming point.
"She's yours, Tom," Tibbets said to the bombardier, veteran of 63 combat missions in Europe.
"I've got it," Ferebee replied.