Actually neither is really true. The “gun type” weapon, the one that was dropped on Hiroshima, they were certain would work and didn’t even need to be tested. Uranium 235 being so scarce and laborious to produce.
Plutonium was different, and the calculations indicated that the “gun type” mechanism would not work. The implosive lens type system was very complicated and needed to be tested, and this was the “fat boy” design tested at Trinity site, and later, dropped on Nagasaki, Japan.
One of the physicists wondered briefly if an atomic explosion might ignite the atmosphere, but this was quickly shut down by more calculations. It does make for a good story.
Thank you very much for your clarifications...I did a deeper dive into what you recounted.
Apparently, it was Oppenheimer who had a bet with another scientist and the bet was that the Trinity test would fail. Being that the plutonium implosion type of bomb was just designed and implemented, I would guess that there would be some doubt as to its initial success.
So the statement by Leahy may not have been an example of pompous poorly informed opinion. Or he may have thought that he was opinionating on the failed plutonium “gun-type” weapon.
It was Teller who believed it was possible that the chain reaction after the blast would ignite the atmosphere, and it was Oppenheimer who ran the calculation to show that the atmosphere was not dense enough to support that scenario.
The plutonium bomb was initially tested as a “gun-type” device similar to the uranium bomb. That turned out to be unfeasible. So the scientists had to design the plutonium implosion type. Which was more complicated and had to be tested.
I have read a few books on the Manhattan project but although they are good, they don’t get into the deep, technical details, also, it would seem that my memory failed me a bit here.
Again, thank you for your comments.