Exactly the same as Dresden and Tokyo - start here: http://www.frot.co.nz/design/conspiracies/atomic-bombs-are-a-complete-con-job-they-dont-even-exist/

Hiroshima:

Also check out: http://www.frot.co.nz/design/conspiracies/no-nukes-were-dropped-on-hiroshima-and-nagasaki/