I didn’t know that. Chuck Sweeney, the pilot of Bock’s Car, gives a pretty good accounting of the mission. They were to under orders bomb “visually” even though they had a crude ground mapping radar.
Due to bad weather they had to shift to Nagisaki (Kokura was the primary & it was socked in.) Sweeney was low on fuel having missed a rendevous with a photographic plane. Add in the fact that the bomb was armed prior to take-off, you can pretty much guess that Sweeney’s ‘miracle’ was that the clouds ‘parted’ just enough to allow visual bombing. They really needed to get rid of that puppy as they didn’t have enough fuel to bring it home. (They might have vaporized the Island of Tinnian & all the US servicemen there if they’d crashlanded.
Bottom line: Sweeneys drop was wide of the mark and a more powerful bomb (than Hiroshima’s) did less damage.
I wouldn't have wanted to carry that unwelcome guest home either. I would have dumped it in the sea if I had to (just like that nuke that was dropped a few miles offshore of Savannah - it hasn't bothered anybody and has been there for years - periodically the environmentalists raise a stink, but since nobody knows where it is now and it's probably sunk deep in the mud, nobody can do anything about it.)