Well, that really is pretty big, but it’s important to note that as bombs go, Hiroshima wasn’t all that big. The destruction was mostly a result of the japanese construction being highly flamable, and when exposed to heat it all went up.
Now, if they compared it to the Tsar Bomba, that would be something. :)
Same happened in Tokyo with the conventional bombing.
15 kilotons
Instant death radius 1.1 miles
It was good enough
And would still quake all but the most determined
And aside from the material being fairly difficult to procure
The bomb itself is not difficult to make for someone relatively skilled with metals and wiring and primary powders ...
Especially if they are less concerned over the survival of the deliverer or use the bomb stationary with a timer or remote trigger or just a very long fuse like mcveigh used
The complication is in the bomb which is sorta typical combustion barometric altitude trigger compilation
The hard part was all the buildup to how does cordite exploding and hence forcing two varyingly enriched sets of uranium rings into one another down a barrel make a Big Bang .....