This concern was soon removed, however, for when we brought the matter to the attention of the Joint Chiefs, they hastily reserved our targets from all air attack.
We were fairly sure by now that we would be able to test the Fat Man, the implosion-type bomb, sometime around the middle of July. (At no time was there any idea of testing the gun-type bomb.) Planning for this operation, which carried the code name of Trinity, had begun back in the spring of 1944 when Oppenheimer and I decided that a test might be necessary to make certain that the complex theories behind the implosion bomb were correct, and that it was soundly designed, engineered, manufactured and assembled—in short, that it would work.
We thought then that we might want to explode the first bomb inside a container, so that if a nuclear explosion did not take place or if it was a very small one, we might be able to recover all or much of the precious plutonium. Also, we wanted to prevent its being scattered over a wide area and creating a health hazard that would make it necessary to guard the area against trespassers for many years.
Consequently we ordered from Babcock and Wilcox a heavy steel container, which because of its great size, weight and strength was promptly christened Jumbo. To move it from the manufacturing plant in the East to New Mexico, it had to be loaded onto specially reinforced cars and carefully routed over the railroads. At the nearest railroad stop to the test site it was unloaded onto a specially built trailer with some thirty-six large wheels, and then driven overland about thirty miles to Alamogordo.
But by the time of the test we had decided we would not need to use Jumbo, for we had learned enough to be reasonably certain of a fair-sized nuclear explosion. Even if it were as low as 250 tons, as many of our scientists were predicting, the container would only create additional dangers.
It is interesting to speculate about what would have happened, with the actual explosion of almost twenty thousand tons, if we had used Jumbo. That the heat would have completely evaporated the entire steel casing is doubtful. If it did not, pieces of jagged steel would probably have been hurled for great distances.
The scientist in charge of the test was Dr. K. T. Bainbridge, who had the unusual qualification of being a physicist with undergraduate training in electrical engineering.
[…]
I had ruled out using Los Alamos for the test on grounds of security and also because I doubted if the area could be expanded sufficiently. Later, we decided that we would need a site measuring approximately seventeen by twenty-four miles, that it should be in a generally non-populated area, and that it should be no further from Los Alamos than necessary. I added one special prohibition: that it should have no Indian population at all, for I wanted to avoid the impossible problems that would have been created by Secretary of the Interior Harold L. Ickes, who had jurisdiction over the Bureau of Indian Affairs. His curiosity and insatiable desire to have his own way in every detail would have caused difficulties and we already had too many.
[…]
Air travel has improved considerably since those days. The field we used at Pasadena was very small, and our approach to it was impeded by some high-tension lines at the end of the strip. As he came in, our pilot found himself lined up on the taxiway and quite low. Instead of circling the field, he came in over the wires and then side-slipped, landing with a terrific bounce—both horizontal and vertical. Our landing brought everyone out of the small operations office, including one of my security officers who had missed the plane in San Francisco, and who was waiting to rejoin us in Pasadena. He remarked afterward that, if not the first, at least the second thought that flashed through his mind was: “How am I going to explain the accidental death of Bush, Conant and Groves, without publicity to the project and resulting breaches of security?”
We left the next morning from March Field in Riverside in order to be sure that the predicted Los Angeles fog would not interfere with our taking off.
[…]
The main problem was the weather. We had obtained the very best men that the armed forces had on long-range weather forecasting, and, for a considerable period, they had been making accurate long-range weather predictions for the test site. The only time they were not right was on the one day that counted. The weather that evening was quite blustery and misty, with some rain. Fortunately, the wind seemed to be in the right direction.
We were interested in the weather for a number of reasons: First and foremost, we wanted to avoid as much radioactive fallout2 as possible, particularly over populated areas. This was a matter that had not received any attention until about six months earlier, when one of the Los Alamos scientists, Joseph Hirschfelder, had brought up the possibility that it might be a real problem. For this reason, we felt it would be desirable to explode the bomb when rain was unlikely, since rain would bring down excessive fallout over a small area instead of permitting it to be widely distributed and therefore of little or no consequence. In reaching this decision we could not ignore the old reports that heavy battle cannonading had sometime brought on rain, even though no scientific basis was known for a such phenomenon.
Second, it was extremely important that the wind direction be satisfactory, because we did not want the cloud, if one developed, to pass over any populated areas until its radioactive contents were thoroughly dissipated. It was essential that it not pass over any town too large to be evacuated. The city about which we were most concerned was Amarillo, some three hundred miles away, but there were others large enough to cause us worry. The wind direction had to be correct to within a few degrees.
Third, we wanted suitable flying weather so that we could have observation planes flying over the near-by areas; and finally, we wanted to avoid prior heavy rain or continuous dampness, which might ruin our electrical connections, both for firing the bomb, and for the various instruments.
[…]
I was extremely anxious to have the test carried off on schedule. One reason for this was that I knew the effect that a successful test would have on the issuance and wording of the Potsdam ultimatum. I knew also that every day’s delay in the test might well mean the delay of a day in ending the war; not because we would not be ready with the bombs, for the production of fissionable material would continue at full tilt anyway, but because a delay in issuing the Potsdam ultimatum could result in a delay in the Japanese reaction, with a further delay to the atomic attack on Japan. Obviously, a reasonable time had to be allowed for the Japanese to consider the ultimatum.
From a purely technical point of view, also, it was desirable to avoid a postponement, for the chances of short circuits and a misfire would increase appreciably with every hour that our connections were subjected to excessive moisture.
[…]
It had originally been scheduled for 4 a.m. on July 16. This hour had been fixed with the thought that an explosion at that time would attract the least attention from casual observers in the surrounding area, since almost everyone would be asleep. We expected there would be a tremendous flash of light, but thought it would not be great enough to waken many people who were well removed from the burst. Then, too, we wanted the darkness for our photography.
[…]
As the hour approached, we had to postpone the test—first for an hour and then later for thirty minutes more—so that the explosion was actually three and one half hours behind the original schedule. While the weather did not improve appreciably, neither did it worsen. It was cloudy with light rain and high humidity; very few stars were visible. Every five or ten minutes, Oppenheimer and I would leave the dugout and go outside and discuss the weather. I was devoting myself during this period to shielding Oppenheimer from the excitement swirling about us, so that he could consider the situation as calmly as possible, for the decisions to be taken had to be governed largely by his appraisal of the technical factors involved.
[…]
Everyone was told to lie face down on the ground, with his feet toward the blast, to close his eyes, and to cover his eyes with his hands as the countdown approached zero. As soon as they became aware of the flash they could turn over and sit or stand up, covering their eyes with the smoked glass with which each had been supplied.
[…]
As I lay there, in the final seconds, I thought only of what I would do if, when the countdown got to zero, nothing happened. I was spared this embarrassment, for the blast came promptly with the zero count, at 5: 30 A.M., on July 16, 1945.
My first impression was one of tremendous light, and then as I turned, I saw the now familiar fireball. As Bush, Conant and I sat on the ground looking at this phenomenon, the first reactions of the three of us were expressed in a silent exchange of handclasps. We all arose so that by the time the shock wave arrived we were standing.
I was surprised by its comparative gentleness when it reached us almost fifty seconds later. As I look back on it now, I realize that the shock was very impressive, but the light had been so much greater than any human had previously experienced or even than we had anticipated that we did not shake off the experience quickly.
Unknown to me and I think to everyone, Fermi was prepared to measure the blast by a very simple device. He had a handful of torn paper scraps and, as it came time for the shock wave to approach, I saw him dribbling them from his hand toward the ground. There was no ground wind, so that when the shock wave hit it knocked some of the scraps several feet away. Since he dropped them from a fixed elevation from near his body which he had previously measured, the only measurement he now needed was the horizontal distance that they had traveled. He had already calculated in advance the force of the blast for various distances. So, after measuring the distance on the ground, he promptly announced the strength of the explosion. He was remarkably close to the calculations that were made later from the data accumulated by our complicated instruments.
I had become a bit annoyed with Fermi the evening before, when he suddenly offered to take wagers from his fellow scientists on whether or not the bomb would ignite the atmosphere, and if so, whether it would merely destroy New Mexico or destroy the world. He had also said that after all it wouldn’t make any difference whether the bomb went off or not because it would still have been a well worth-while scientific experiment. For if it did fail to go off, we would have proved that an atomic explosion was not possible. Afterward, I realized that his talk had served to smooth down the frayed nerves and ease the tension of the people at the base camp, and I have always thought that this was his conscious purpose. Certainly, he himself showed no signs of tension that I could see.
[…]
These plans proved utterly impracticable, for no one who had witnessed the test was in a frame of mind to discuss anything. The reaction to success was simply too great. It was not only that we had achieved success with the bomb; but that everyone—scientists, military officers and engineers—realized that we had been personal participants in, and eyewitnesses to, a major milestone in the world’s history and had a sobering appreciation of what the results of our work would be. While the phenomenon that we had just witnessed had been seriously discussed for years, it had always been thought of as a remote possibility—not as an actuality.
[…]
Several days after I got back to Washington, Dr. R. M. Evans, of the du Pont Company, came to see me about some of the operating problems at Hanford. After we had finished and as he was leaving, he turned, his hand on the doorknob, and said, “Oh, by the way, General, everybody in du Pont sends you their congratulations.” I quickly replied, “What are you talking about?” He answered, “It’s the first time we ever heard of the Army’s storing high explosives, pyrotechnics and chemicals in one magazine.” He went on to add that the radio announcement on the Pacific Coast had been teletyped in to Wilmington from Hanford. My only response was: “That was a strange thing for the Army to do, wasn’t it?”
[…]
Mr. Stimson’s diary for Sunday, July 22, 1945, is most enlightening:
Churchill read Groves’ report in full. He told me that he had noticed at the meeting of the Three yesterday that Truman was much fortified by something that had happened, that he had stood up to the Russians in a most emphatic and decisive manner, telling them as to certain demands that they could not have and that the United States was entirely against them. He said, “Now I know what happened to Truman yesterday. I couldn’t understand it. When he got to the meeting after having read this report, he was a changed man. He told the Russians just where they got on and off and generally bossed the whole meeting.” Churchill said he now understood how this pepping up had taken place and he felt the same way.
