I didn't understand how true this was until someone in the pebble reactor camp pointed out that these ideas were already known before the Manhattan project, and that there was a moment where the direction of investment was still up in the air and the war hawks won. I figured that was something someone discovered in the 80's and took a while to popularize. Nope.
This is a weird history of nuclear fission.
The Manhattan project developed nuclear fission to make bombs
The weapons programs were extended to generate power