This would not work with plutonium, which is what Philip’s “Nagasaki-like” (Wikipedia) design apparently used. The gun design does not create the critical confi

This would not work with plutonium, which is what Philip’s “Nagasaki-like” (Wikipedia) design apparently used. The gun design does not create the critical configuration fast enough to prevent it ‘fizzling’ - the assembly blowing itself apart before the chain reaction has progressed far enough for a nuclear-scale explosion. Instead, you need an implosion device. This is much more challenging, requiring explosive lenses (precisely-shaped charges), multiple precisely-timed detonators, and an initiator that will produce a burst of neutrons just as the explosive’s shock waves reach the center of the fissile assembly. I am sure you are right, though, that the bill of materials did not include the fissile material. Anyone surprised by Phillip’s result was perhaps assuming that it would take something like the Manhattan Project to independently design a bomb.