WW2 bombs of this size where and of course still would be incredibly powerful before the Nuclear bombs were detonated and we entered the nuclear age "conventional" munitions had already hit the point where an entire city could be destroyed in a few attacks.
For those interested in this sort of thing look up attacks on Dresden ,Hamburg and Tokyo.
"Night of 9-10 Mar, Operation Meetinghouse: 279 B-29 bombers dropped incendiary bombs and destroyed 267,000 buildings and homes or 41 square kilometers of Tokyo. Americans estimated 88,000 killed, 41,000 injured, and 1,000,000 displaced. Tokyo Fire Department estimated 97,000 killed and 125,000 wounded. Tokyo Metropolitan Police Department estimated 124,711 casualties and 286,358 destroyed buildings and homes."
Ok that was nearly 300 planes but i am sure you get the point.
For the anti nuclear lobby its worth noting that we could wipe out a city quite happily even without the "A" bomb.