Report of the British Mission to Japan
Hiroshima
Typical small earth-covered back yard shelter with crude wooden frame, less than 100 yds. from the centre of damage which is to the right. There was a large number of such shelters, but whereas nearly all those, as close as tins one had their roofs forced in, only half were damaged at 300 yds., and practically none at half a mile from the centre of damage. See paragraph 41.