Each with and incendiary charge and the GPS coordinates of every home/building in a city. Who needs Tokyo/Dresden firebombing anymore.
Which is something the US actually tried. https://en.wikipedia.org/wiki/Bat_bomb
In this particular context, if you're thinking of WWII, it's kind of odd for a person not to think of and compare the concept to https://en.wikipedia.org/wiki/Fu-Go_balloon_bomb
This could be due to some agenda to shame the Allies for their involvement in WW2, or it could just be because WW2 is really the only time in history it was done on that scale and the Allies happened to win the conflict.
I'm going to go with principle of charity and assume the latter...