In message , at 14:56:57 on Tue, 12
Oct 2010, AndyW remarked:
IIRC, the Japanese got the Hiroshima message just fine, and probably
would've surrendered given a bit more time. Nagasaki was sending a
totally different message: telling the Soviets that the first nuke
wasn't a fluke.

The first was a simple bomb to shock the Japanese, the second was a
effectively a field test of a different type of nuke.
The first one was a simple, ineffecient but reliable design that basically
involved slamming two subcritical masses of uranium together. Fairly sure
that it would work.
The second was much more risky design involving compressing plutonium very
precisely to increase neutron density enough to start a chain reaction.
There was a risk that this would not work as it pushed engineering to it's
limit. Bad idea to use it as a message, as it happened it was a very
effective message.

But if it hadn't worked, surely they'd just keep schtum about it, and
try again another day.
--
Roland Perry