[kps]

Japan didn't know until August 9 that the US was able to build plutonium bombs.

Edit since I can't reply: The difference is meaningful when you're deciding whether to surrender. If you know that the US doesn't have enough refined uranium for another uranium bomb, and you have no evidence that the US can build plutonium bombs, then you have grounds to believe the bombing of Hiroshima was not repeatable.

[throw0101d]

> If you know that the US doesn't have enough refined uranium for another uranium bomb […]

There was no way for the Japanese to know what the US was capable of. It was wishful thinking with zero evidence on the part of the Japanese leadership.

[WalterBright]

> There was no way for the Japanese to know what the US was capable of.

The Japanese had their own bomb program underway.

[littlestymaar]

So did the Germans, but it's not because the biggest industrial power on earth (in both demography and industrial output), with its capacities fully intact because the war never took place there, that smaller countries diminished after years of blockade and critical infrastructure bombing can do it too…

If the Japanese projected their own capacity on the US, they were ripe for a bad surprise.