Both atomic bombs detonated in Japan during World War II did not hit the ground before exploding. The hilly terrain of Nagasaki protected the region somewhat from the blast, whereas the flatter layout of Hiroshima left it more vulnerable and exposed to the full force of the atomic bomb.
The first bomb, code-named "Little Boy," exploded 2,000 feet above the city of Hiroshima. The second bomb, which was code-named "Fat Man," detonated at a height of 1,800 feet above the city of Nagasaki. Fat Man had a heavier payload than Little Boy, as the names imply, but Little Boy was more destructive, taking out 5 miles of the city as compared to Fat Man's 2.6 miles.