I would add that at the time when the bomb was dropped on Japan, it also wasn't entirely clear what it really means. For everyone in the military, it was just one Big Effing Bomb, nothing more. Not very much unlike the MOAB nowadays.
That radiation and fallout are scarier than the blast, it took a very long time to sink in.
Remember that at the time, there were Fluoroscopes (read, X-Ray machines) even in shoe stores, so people could see how their foot fits in various shoes. And they were not the modern low-radiation kind. The only light on the screen came from the X-Rays themselves exciting the coating, so to be usable in broad daylight, they pumped enough radiation through people's feet and shop employees to sometimes outright cause immediate radiation burns.
They kept being used willy nilly like that until well into the 50's.
The USA itself exposed some of its own troops needlessly to radiation and fallout, just to test its what-to-do-when-nuked tactics and partially just to see what happens.
It took a long time for the "radiation = effing scary" idea to sink in, and partially that's what made the cold war work when it did. Both powers were a lot more inclined to think of nukes as just freaking huge explosives in the beginning, and thought they can just tell their troops to duck and cover in the trenches. ETA: They even came up with ideas as dumb as _tactical_ nukes, really, small rockets or even artillery shells you'd lob at the enemy a couple of miles from your own position, at the time.
