Nowadays we learn about these events through many mediums with television having shown us many moments in modern warfare since the late 1900’s onwards but how did the world first learn of the existence of nuclear weapons and their use in warfare?
When did news first break that America had such weapons of mass destruction? When the bombs first dropped on Hiroshima, did the Japanese survivors know what hit them? Was the American public’s reaction to the bombing positive or negative and were all the facts of its devastation made available? How did the rest of Japan first learn what happened at Hiroshima and what was the reaction?
When we look at movies like Gojira or works like Barefoot Gen we can see just how it permeated the ?Japanese consciousness after the fact, but what was the knowledge before the bombings?
Thanks in advance to all who answer.
In the United States the announcement of the atomic bombings of Japan was a very well-coordinated publicity/propaganda campaign that had been planned by the people who developed the bombs. They sent out pre-written stories about the bombs, how they were made, etc., to newspapers and radio stations. These accompanied press releases from the President and the Secretary of War. One thing you should remember is that newspapers were far more vibrant in the 1940s than today; not only were there many of them, but they were in such demand that there were often multiple issues per day ("evening" vs. "morning" editions). If you were an American in 1945 you would have gotten the information this way, if not from word of mouth from someone else who had gotten it this way. This information began broadcasting a few hours after the Hiroshima attack.
In Japan, the situation was somewhat different. Concurrent with its propaganda/publicity blitz in the US, the US military began broadcasting announcements about the Hiroshima attack over radio towards Japan. This was part and parcel of their general propaganda/"psychological warfare" approach with regards to Japan. They also made propaganda leaflets about the Hiroshima bomb, though these were not dropped until after the Nagasaki attack (for complicated reasons; in short, they hadn't prepared them ahead of time, so the process of making and using them took a few days).
It's not clear to me that the average Japanese citizen would have had access to these announcements. They certainly would not have been encouraged to listen to them. Rather, there was state-run newspaper and radio. The state radio related that Truman had announced that an atomic bomb was dropped on Hiroshima, but did not elaborate beyond that. Some other Japanese radio said Hiroshima had been attacked by B-29s using incendiary devices. It was not until August 8 that newspapers in Japan carried any kind of detailed discussion of the attack, and it was fairly confused. The Japanese cabinet's own survey of Hiroshima had not been completed yet; they were only just confirming it was a "new weapon." By August 9th there were reports of widespread damage and huge casualties in Japanese newspapers.
As for the survivors in Hiroshima, all accounts by them indicate that they initially thought it was a very localized attack that they happened to be in the middle of, and it gradually dawned on them that the entire city had been destroyed. Some reported seeing only one bomber and only one bomb (the difference between being attacked by one B-29 and five hundred is fairly obvious); none knew what they had been attacked by. Some understood it was something different; some thought it was a conventional attack. It was not until some days later that they understood it was an atomic bomb.
As for the longer thread of Japanese understanding and discussion about the atomic bomb — it's a much longer story. Discussion of the atomic bomb and its effects was largely censored within Japan by the US Occupation, who feared that it would cause anti-US sentiment. Study of the attacked cities and survivors continued under joint US-Japanese auspices. Gojira and many 1950s (and later) discussions of the bomb were a reaction both to the end of the US Occupation (1952) and the resurrection of Japanese sentiment following the deaths of Japanese fishermen, and contamination of Japanese tuna, from the US Castle Bravo thermonuclear test in 1954. It was in the mid-1950s that the Japanese solidified their anti-nuclear weapons stance, and began to appropriate Hiroshima and Nagasaki as symbols in a new peace movement that centered around the idea of Japanese nuclear victimhood.
US reactions to the bombings has been complicated, even since the first days of it. While the majority of US population surveyed was enthusiastic about their use against Japan, especially after the bombings were credited (rightly or wrongly) with ending the war, there was always an undertone of uncertainty, because it was recognized that the US had brought this new force into the world, christened it with blood, and that any future major conflict would probably involve such weapons being used against Americans. As a result much of the early discussion of the atomic age was about how to try to contain this new force and avoid its future use — without much success. One sees this uncertainty in the coverage of the bombs even from the day of Hiroshima onward in the US newspapers: immediately the discussion shifted to "what would happen if that happened here?" and discussions about how such weapons could either indicate the end of war (good) or the end of civilization (bad).
There is much more that one can say about the later evolution of US and Japanese views towards nuclear weapons and the atomic bombings; it has been continuous since 1945. Spencer Weart's Nuclear Fear is a great book that discusses shifts in global nuclear attitudes, though it is centered on the US. As for the Japanese, Monica Braw's The Atomic Bomb Suppressed discusses the early days after Hiroshima and during the US Occupation.