Your claim that "there were no civilians in Hiroshima" is incorrect. 

The fact is Hiroshima was primarily a civilian target. The vast majority of deaths and casualties were civilian. The nukes caught hundreds of thousands of women, children and elderly people on their daily activities.

 The target was the t shaped Aioi Bridge in the middle of Hiroshima's residential district to maximize civilian casualties. The epicenter of the strike was mere meters from Honkawa elementary school.