You're correct, but the circumstances of the first atomic attack caused significant delays for accurate information to reach the Imperial General Headquarters.

You're correct, but the circumstances of the first atomic attack caused significant delays for accurate information to reach the Imperial General Headquarters. The first info stated that Hiroshima was devastated in an air raid, but the officers at high command considered this to be an error due to the lack of reports of hundreds of American bombers over the city on that day. However, they were unable to get any communication from Hiroshima (note that the military headquarters was at the Hiroshima Castle which was completely destroyed). It didn't take days, but it did take many hours for Tokyo to realize that indeed Hiroshima was devastated in an attack. Some officers even thought it was a traditional bombing raid and that there was a technical issue or even sabotage with their communication lines between Hiroshima and Tokyo. Tho Officer Corps at first had little knowledge to understand that it might have been an atomic attack, and that therefore the war had changed in a very serious manner.