I did mention that it was called the Plumbbob Series and these were tests which… on alternate explosions. They were either Livermore or Los Alamos. Both of them had devices they were testing.

The Livermore devices were named after mountains and the Los Alamos devices were named after scientists, which I thought was typical of the two institutions. The first explosion that I saw was called Smoky. That was named after the Smoky Mountains and this is the picture that I saw. This is what I saw when I turned around after looking away for 10 seconds. This is what I saw and this picture doesn't really give an idea of the scale. I would suppose that it was.... certainly several football fields in length and the mushroom cloud was just beginning to form, the fireball and so on. It was unbelievably impressive.

Then I mentioned that, after we saw the explosions, which were very early in the morning, we went back to get a little sleep and in the course of this, I heard the sound of these helicopters. And Carson Mark, who was the director of the Theoretical Division who had authorised me to come, was a very droll Canadian. And I said, 'They're flying'. And Carson said, 'They're flying and flying'. Without offering any explanation to who was flying or why they were flying. And I was very much under the stricture of the need to know and I felt that there was nothing that I needed to know and I didn't ask any questions.

But after a while, after years went by; the Plumbbob Series, like the rest of the tests, were kind of unclassified, or partially declassified, so you could learn that in the course of the Plumbbob Series, there were several thousand soldiers who witnessed the test, and they were marched to ground zero. And the helicopters had to do with the manoeuvres of these soldiers, as I learned later.

Some of them got leukaemia, presumably attributable to the exposure to radiation. We didn't get any radiation. I was… we were all something like 10n miles away. But I mentioned last time that the shockwave was certainly noticeable. It was a very, rather unpleasant click in the ear. And as one knows, one of the main sources of damage in Hiroshima was the shockwave, which produced winds that were stronger than any cyclone wind, and knocked over the cooking fires that the Japanese were using, and caused a lot of fire damage in Hiroshima.a