" Rather than sleep, Tibbets crawled through the thirty-foot tunnel to chat with the waist crew, wondering if they knew what they were carrying. "A chemist's nightmare," the tail gunner, Robert Caron, guessed, then "a physicist's nightmare." "Not exactly," Tibbets hedged. Tibbets was leaving by the time Caron put two and two together: 'Tibbets stayed a little longer, and then started to crawl forward up the tunnel. I remembered something else, and just as the last of the Old Man was disappearing, I sort of tugged at his foot, which was still showing. He came sliding back in a hurry, thinking maybe something was wrong. "What's the matter?" I looked at him and said, "Colonel, are we splitting atoms today?" This time he gave me a really funny look, and said, "That's about it. "