In January 1945, US president Roosevelt arranged to bring his son James back from service in the South Pacific so that he could be present at the fourth inauguration.* James said that they still had a lot of fighting to face and that since the invasion of Japan was bound to be bloody, he could not be sure he would ever return to see his father again.
"James," said Roosevelt, "there will be no invasion of Japan. We will have something that will end our war with Japan before any invasion takes place." James asked what it was, but Roosevelt said, "I am sorry; even though you are my son, I cannot tell you. Only those who need to know, know about it. But it is there, it is something we certainly will use before you or any of our sons die in an invasion of Japan."
一九四五年一月，美國總統羅斯福安排兒子詹姆斯回國出席他第四次總統就職儀式*。當時詹姆斯在南太平洋服役，說軍隊還須多處作戰，而進攻日本之戰必然慘烈，他未必能夠活着回國見父親。
羅斯福說：「詹姆斯，我們不會進攻日本。我們有一件東西，可以終止和日本的戰爭，不必進攻。」詹姆斯問那是什麼，羅斯福說：「對不起，你雖然是我兒子，也不能告訴你。這東西，必須知道的人，才會知道，但確實已經在我們手上，也一定會使用，以免你或任何美國人死在進犯日本的戰事之中。」
*羅斯福是美國唯一四度當選的總統，其後國會立法，禁止總統任期超過兩屆。