The six crews that might be used were given special instructions on the procedures they were to follow, and at another briefing on August 4, Parsons explained the effects they could expect when the bomb exploded. Most of them knew by now that they were dealing with a special type of bomb, but Parsons’ statement that the force of the explosion would be equivalent to that of twenty thousand tons of TNT came as a complete surprise.
During the period of waiting, the special air-sea rescue plans were settled. They emphasized that no other aircraft would be permitted within fifty miles of the target during a period of from four hours before until six hours after strike time. Not even for rescue operations would this restriction be lifted. Special air-sea rescue facilities were to be provided by both Army and Navy planes and by submarines, and in spite of the necessary restrictions we had placed upon it, rescue coverage in this operation would be far better than average.
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Other air attacks on Japan were to be carried out on the same day as our mission, to divert any Japanese defense actions that might endanger our operation. Hiroshima would be the primary target, with Kokura Arsenal and Kokura the secondary targets, and Nagasaki the tertiary target. The aiming point for Hiroshima was close to the Japanese Army Headquarters.
Hiroshima was a highly important military objective. The Army Headquarters was located in a castle. Some 25,000 troops were in its garrison. It was the port through which all supplies and communications passed from Honshu to Kyushu. It was the largest city, excepting Kyoto, that was still undamaged by American air raids. Its population was believed to be over 300,000, and it was a beehive of war industry, carried on in moderate-sized plants and in small shops as well as in almost every home.
We would use a total of seven planes. One would be sent to Iwo Jima to serve as a spare in case the bomb-carrying plane developed mechanical troubles on the flight from Tinian. Three planes would go ahead, one to each target area, to appraise the local weather and to relay the information back to the bomb-carrying plane, which would be accompanied by two observer planes to the general vicinity of the target. One of these carried special measuring and recording instruments, including some that would be dropped near the target to radio back their readings.
Radar was to be used as an aid but the actual bombing was to be accomplished visually. If this proved to be impossible, the bomb was to be brought back, probably to Iwo Jima, as the plane’s gas supply might not permit the return to Tinian. We were anxious to avoid having it come down at other air bases, for in case of a landing accident we wanted personnel on the ground who would be aware of the special precautions that would have to be taken.
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Provisions were also made for the strike photographs to be taken by the 3rd Photo Reconnaissance Squadron and two photo crews were briefed on their assignment by the 509th’s intelligence officers.
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Parsons had decided with Farrell’s approval to complete the final assembly of the bomb after takeoff. His purpose was to minimize the hazards of a crash on Tinian. I had previously said that I was opposed to this as unwise, because it was unnecessary and because it would be very difficult to do it in cramped conditions in the plane. I was not informed of the plan until it was too late to interfere.
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The original scheduled time was 0915. Thus, in a flight of some seventeen hundred miles taking six hours and a half, Colonel Tibbets had arrived on target only one-half of a minute off schedule.
The 20th Air Force order covering the operation prescribed a turn of 150° after the bomb was released in order to gain a maximum distance from the point of explosion; such a turn, our studies indicated, could be made without undue risk to the plane and its crew.
Immediately after the bomb was dropped from 31,600 feet, the plane began its getaway maneuver. The flash was seen during this turn and fifty seconds after the drop, the shock waves hit the plane. There were two of these, the first the direct shock wave and the second the reflected wave from the ground. By that time the plane was fifteen miles away from the burst.
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The crews of the strike and the two observation aircraft reported that five minutes after release a dark gray cloud of some three miles in diameter hung over the center of Hiroshima. Out of the center of this grew a column of white smoke which rose to a height of 35,000 feet, with the top of the cloud being considerably enlarged.
Four hours after the strike, the photo reconnaissance planes found that most of the city of Hiroshima was still obscured by the smoke cloud, although fires could be seen around its edges.
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Pictures taken the following day showed that 60 per cent of the city was destroyed.
The area devastated at Hiroshima was 1.7 square miles, extending out a mile from ground zero. The Japanese authorities estimated the casualties at 71,000 dead and missing and 68,000 injured.
The most important result achieved by the Hiroshima bombing was not the physical damage, although over 50 per cent of the buildings were totally destroyed, nor was it the fifteen to twenty thousand Japanese soldiers who were killed or severely wounded, nor was it the thousands of other people killed and injured. The important result, and the one that we sought, was that it brought home to the Japanese leaders the utter hopelessness of their position. When this fact was re-emphasized by the Nagasaki bombing, they were convinced that they must surrender at once.
Parsons reported (in special one-time code, of course):
Results clearcut, successful in all respects. Visible effects greater than New Mexico tests. Conditions normal in airplane following delivery.
Received at the same time was this message relayed from the plane:
Target at Hiroshima attacked visually. One-tenth cloud at 052315Z. 3 No fighters and no flak.
At about 4:30 a.m. the Duty Officer delivered General Groves the detailed hoped-for cable from Farrell, as Groves explains (in Now It Can Be Told: The Story of the Manhattan Project), which had been dispatched after the bomber returned to Tinian. It read: