My father also flew out of Guam on B-29’s. He was the Co-Pilot and said he was on Tinian when the bomb arrived,he said he had no idea what it was. He died in 1992 of ALS (Lou Gehrig disease).
3 of us ended also serving the U.S. Air Force, mostly from the inspiration from dad.
There's a great book out there titled, The Last Mission.
It chronicles it well.
http://pweb.netcom.com/~jb29miss/