From Science Alert:
As it turns out, this was the first time the Japanese public at large had ever heard one of their emperors’ voices, but for scientists at the Los Alamos Laboratory in New Mexico – aka Project Y – the event had a more pressing significance.
It meant the functional heart of the third atom bomb they’d been working on – a 6.2-kilogram (13.7-pound) sphere of refined plutonium and gallium – wouldn’t be needed for the war effort after all. If the conflict had still been raging, as it had for almost five straight years, this plutonium core would have been fitted into a second Fat Man assembly and detonated above another unsuspecting Japanese city just four days later.