We worked with a Dr. Edward Doll, a civilian with a Ph.D. from Caltech in electrical engineering who was our immediate boss in charge of the electronics of the weapons. There were the same electronics in both Hiroshima and Nagasaki, but different types of bombs. We were being trained to help with the development of the electronics in the fusing system, and then to fly these things when it was finally developed and the bomb was ready. Radar is very critical. Dropped from 30,000 ft., the bombs weighed 5 tons and they were approaching the ground at the speed of sound. They were intended to have maximum blast effect so they could not be detonated when they hit the ground because the ground would absorb a lot of the energy. They had to be detonated above the ground, at about 1500-1800 ft. At 1500 ft above the ground, you only have one and a half seconds for this thing to decide it’s going to detonate when it’s supposed to.
On one of the trips to Los Alamos, I went in the library to see if I could learn what was going on. The words “nuclear” and “atomic” were never permitted to be spoken outside of that high-tech area of Los Alamos. It was never spoken at Wendover. I found a well-worn book that had been withdrawn from publication but one that talked about the nuclear fission and possibility of making of atomic bombs, so I realized that that’s what we were working on.
The B-29s would fly with test bombs and drop it on targets on the Salton Sea desert and one of our group would go with each mission. We moved our test equipment from one plane to another and didn’t develop relationships with any particular crew. We were not crew memberswe moved from one to another. Our program moved overseas in June of 1945 to Tinian Island. There were four big runways and 400 B-29s based there, and several more based in Guam and Saipan. And now we’re flying the Hiroshima mission.
Most people don’t know the fact the Enola Gay had stenciled on its nose the names of just the nine crew members, the normal crew members. But there were three others on board, and one of them was Captain William S. Parsons, who was in military command of Los Alamos. In other words, he and Oppenheimer ran Los Alamos. He was the mission commander. If anything went wrong, this particular mission was valued at $2 billion. I was to tell him if there was a problem and I was to tell him also if the problem was serious enough that they should take the bomb back to Tinian
We had breakfast after midnight and were taken by a truck out to the plane. My role was to test the electronics on the bomb all the way from the battery that operated the circuitry to the timing clocks and the barometric switches and the radars that had to be turned on.
The arming of the bomb was about half an hour before the bomb was dropped. My last job was to climb into the bomb bay and remove those three testing plugs, painted green and each about the size of a saltshaker. Those plugs isolated the testing system from the bomb, so there was no chance of any voltage getting from the bomb to the testing system. I pulled those plugs and put in three red firing plugs to arm the bomb. From that point on, the bomb was running itself.
The focus was entirely on making sure that thing worked. I knew from test drops that it took about 43 seconds from the time that the plane jerked up--when the bomb left--to the time of the flash or explosion. I counted to myself to 43. Nothing happened, and that was my moment of real worry. A couple of seconds later, the flash came--reported by people from the front of the plane--and I knew that I had miscounted the time and that the thing actually worked.
People were looking down and seeing this enormous cloud coming up and the destruction spreading out from the base--with flames and black smoke and white smoke. And that's the point that it's somber because you know a lot of people are getting destroyed down there with the city. No joy at that point. But it was a job that was done.
Everyone by this time was tired. When we landed, the plane was greeted by several hundred people, a whole group of Army, Navy, Air Force generals and admirals. I was lost in the crowd, so it didn't make any difference. The crew went off to a debriefing. Nobody knew particularly what my role or our group's role was, so I went back to my tent. Sitting on the edge of my bunk was a Navy lieutenant whom I had grown up with from the first grade--my best friend Jack Scott. I didn't know he was even on the island, but he said, "Come to the Navy base on the other end of the island. We have a good officers' mess there, and we'll have a good meal and a good bar." So we drove down there and had dinner, and there were several Navy officers there. One of them turned to me and asked, "What did you do today?" I'd heard a lot of their stories, so I thought I'd make just one remark. I said, "I think we ended the war today."
A shorter version of this account appears in the Aug. 1, 2005 issue of TIME Magazine