the weapon was designed at Los Alamos but decided upon at Tinian, for safety on takeoff and in the event visual bombing proved impossible, in which case Tibbets had orders to bring the bomb back. Three of Tibbets' full complement of fifteen B-29's flew a last test that last day of July with a dummy Little Boy. They took off from Tinian, rendezvoused over Iwo Jima, returned to Tinian, dropped unit L6 into the sea and practiced their daredevil diving turn. “With the completion of this test,” writes Norman Ramsey, “all tests preliminary to combat delivery of a Little Boy with active material were completed.” That unit would be number Lll, and the sturdy tungsten-steel target holder screwed to its muzzle, the best in stock, was the first one Los Alamos had received; it had served four times for firing tests at Anchor Ranch late in 1944 before being packed in cosmoline for the voyage out to Tinian.
Since everything was ready, Farrell telexed Groves to report that the mission could be flown on August 1; he would assume that the Spaatz directive of July 25 authorized such initiative unless Groves replied to the contrary. The commanding general of the Manhattan Project let his deputy's interpretation stand. Little Boy would have flown on August 1 if a typhoon had not approached Japan that day to intervene.
So the mission waited on the weather. On August 2, Thursday, the three B-29's that carried Fat Man preassemblies arrived from New Mexico. The assembly team of Los Alamos scientists and military ordnance technicians went to work immediately to prepare one Fat Man for a drop test and a second with higher-quality HE castings for combat. The third preassem-bly would be held in reserve for the plutonium core scheduled to be shipped from Los Alamos in mid-August. “By August 3,” recalls Paul Tib-bets, “we were watching the weather and comparing it to the [long-range] forecast. The actual and forecast weather were almost identical, so we got busy.”
Among other necessities, getting busy involved briefing the crews of the seven 509th B-29's that would fly the first mission for weather reporting, observation and bombing. Tibbets scheduled the briefing for 1500 hours on August 4. The crews arrived between 1400 and 1500 to find the briefing hut completely surrounded by MP's armed with carbines. Tibbets walked in promptly at 1500; he had just returned from checking out the aircraft he intended to use to deliver Little Boy, usually piloted by Robert Lewis: B-29 number 82, as yet unnamed. Deke Parsons joined him on the briefing platform. A radio operator, Sergeant Abe Spitzer, kept an illegal diary of his experiences at Tinian that describes the briefing.
The moment had arrived, Tibbets told the assembled crews. The weapon they were about to deliver had recently been tested successfully in the United States; now they were going to drop it on the enemy.
Two intelligence officers undraped the blackboards behind the 509th commander to reveal aerial photographs of the targets: Hiroshima, Kokura, Nagasaki. (Niigata was excluded, apparently because of weather.) Tibbets named them and assigned three crews — “finger crews” — to fly ahead the day of the drop to assess their cloud cover. Two more aircraft would accompany him to photograph and observe; the seventh would wait beside a loading pit on Iwo Jima as a spare in case Tibbets' plane malfunctioned.
The 509th commander introduced Parsons, who wasted no words. He told the crews the bomb they were going to drop was something new in the history of warfare, the most destructive weapon ever made: it would probably almost totally destroy an area three miles across.
They were stunned. “It is like some weird dream,” Spitzer mused, “conceived by one with too vivid an imagination.”
Parsons prepared to show a motion picture of the Trinity test. The projector refused to start. Then it started abruptly and began chewing up leader. Parsons told the projectionist to shut the machine off and improvised. He described the shot in the Jornada del Muerto: how far away the light had been seen, how far away the explosion had been heard, the effects of the blast wave, the formation of the mushroom cloud. He did not identify the source of the weapon's energy, but with details — a man knocked down at 10,000 yards, men 10 and 20 miles away temporarily blinded — he won their rapt attention.
Tibbets took over again. They were now the hottest crews in the Air Force, he warned them. He forbade them to write letters home or to discuss the mission even among themselves. He briefed them on the flight. It would probably go, he said, early on the morning of August 6. An air-sea rescue officer described rescue operations. Tibbets closed with a challenge, a final word Spitzer paraphrases in his diary:
The colonel began by saying that whatever any of us, including himself, had done before was small potatoes compared to what we were going to do now. Then he said the usual things, but he said them well, as if he meant them, about how proud he was to have been associated with us, about how high our morale had been, and how difficult it was not knowing what we were doing, thinking maybe we were wasting our time and that the “gimmick” was just somebody's wild dream. He was personally honored and he was sure all of us were, to have been chosen to take part in this raid, which, he said — and all the other big-wigs nodded when he said it — would shorten the war by at least six months. And you got the feeling that he really thought this bomb would end the war, period.
The following morning, Sunday, Guam reported that weather over the target cities should improve the next day. “At 1400 on August 5,” Norman Ramsey records, “General LeMay officially confirmed that the mission would take place on August 6.”
That afternoon the loading crew winched Little Boy onto its sturdy transport dolly, draped it with a tarpaulin to protect it from prying eyes — there were still Japanese soldiers hiding out on the island, hunted at night by security forces like raccoons — and wheeled it to one of the 13 by 16-foot loading pits Kirkpatrick had prepared. A battery of photographers followed along to record the proceedings. The dolly was wheeled over the nine-foot pit on tracks; the hydraulic lift came up to relieve it of its bomb and detachable cradle; the crew wheeled the dolly away, removed the tracks, rotated the bomb 90 degrees and lowered it into the pit.
The world's first combat atomic bomb looked like “an elongated trash can with fins,” one of Tibbets' crew members thought. With its tapered tail assembly that culminated in a boxed frame of stabilizing baffle plates it was 10 feet long and 29 inches in diameter. It weighed 9,700 pounds, an armored cylinder jacketed in blackened dull steel with a flat, rounded nose. A triple fusing system armed it. The main fusing component was a radar unit adapted from a tail-warning mechanism developed to alert combat pilots when enemy aircraft approached from behind. “This radar device,” notes the Los Alamos technical history, “would close a relay [i.e., a switch] at a predetermined altitude above the target.” For reliability Little Boy and Fat Man each carried four such radar units, called Archies. Rather than an approaching enemy aircraft, the bomb Archies would bounce their signals off the approaching enemy ground. An agreed reading by any two of the units would send a firing signal into the next stage of the fusing system, the technical history explains:
This stage consisted of a bank of clock-operated switches, started by arming wires which were pulled out of the clocks when the bomb dropped from the plane's bomb bay. These clock switches were not closed until 15 seconds after the bomb was released. Their purpose was to prevent detonation in case the A[rchie] units were fired by signals reflected from the plane. A second arming device was a [barometric] pressure switch, which did not close until subject to a pressure corresponding to 7000 feet altitude.
Once it passed through the clock and barometric arming devices the Little Boy firing signal went directly to the primers that lit the cordite charges to fire the gun. Externally the fusing system revealed itself in trailing whips of radar antennae, clock wires threaded into holes in the weapon's upper waist and holes in its tapered tail assembly that admitted external air to guarantee accurate barometry.
Loading the bomb was delicate: the fit was tight. A ground crew towed the B-29 to a position beside the loading pit, running onto a turntable the main landing gear on the wing nearer the pit. Towing the aircraft around on the turntable through 180 degrees positioned it over the pit. The hydraulic lift raised Little Boy to a point directly below the open bomb doors. A plumb bob hung from the single bomb shackle for a point of reference and jacks built into the bomb cradle allowed the crew to line up the bomb eye.
“The operation can be accomplished in 20 to 25 minutes,” a Boeing engineer commented in an August report, “but is a rather ticklish procedure, as there is very little clearance with the catwalks and, once installed, nothing holds the bomb but the single shackle and adjustable sway braces bearing on it.”
Though he flew it as his own, Robert Lewis had never named B-29 number 82. The day of the loading Tibbets consulted the officers in Lewis' crew — but not Lewis — and did so. The 509th commander chose not pinups
