1939年8月2日，愛因斯坦出於對人類命運的極大關註，應其他幾位科學家的請求，寫信建議美國務必搶在德國之前制造出原子彈。壹封由別人起草、愛因斯坦簽名的信中寫道：
Albert Einstein
Old Grove Rd.
Nassau Point
Peconic, Long Island
August 2nd, 1939
F.D. Roosevelt
President of the United States
White House
Washington, D.C.
Sir:
Some recent work by E.Fermi and L. Szilard, which has been communicated to me in manuscript, leads me to expect that the element uranium may be turned into a new and important source of energy in the immediate future. Certain aspects of the situation which has arisen seem to call for watchfulness and, if necessary, quick action on the part of the Administration. I believe therefore that it is my duty to bring to your attention the following facts and recommendations:
In the course of the last four months it has been made probable – through the work of Joliot in France as well as Fermi and Szilard in America – that it may become possible to set up a nuclear chain reaction in a large mass of uranium by which vast amounts of power and large quantities of new radium-like elements would be generated. Now it appears almost certain that this could be achieved in the immediate future.
This new phenomenon would also lead to the construction of bombs, and it is conceivable – though much less certain – that extremely powerful bombs of a new type may thus be constructed. A single bomb of this type, carried by boat and exploded in a port, might very well destroy the whole port together with some of the surrounding territory. However, such bombs might very well prove to be too heavy for transportation by air.
The United States has only very poor ores of uranium in moderate quantities. There is some good ore in Canada and the former Czechoslovakia, while the most important source of uranium is Belgian Congo.
In view of the situation you may think it desirable to have more permanent contact maintained between the Administration and the group of physicists working on chain reactions in America. One possible way of achieving this might be for you to entrust with this task a person who has your confidence and who could perhaps serve in an inofficial capacity. His task might comprise the following:
a) to approach Government Departments, keep them informed of the further development, and put forward recommendations for Government action, giving particular attention to the problem of securing a supply of uranium ore for the United States;
b) to speed up the experimental work, which is at present being carried on within the limits of the budgets of University laboratories, by providing funds, if such funds be required, through his contacts with private persons who are willing to make contributions for this cause, and perhaps also by obtaining the co-operation of industrial laboratories which have the necessary equipment.
I understand that Germany has actually stopped the sale of uranium from the Czechoslovakian mines which she has taken over. That she should have taken such early action might perhaps be understood on the ground that the son of the German Under-Secretary of State, von Weizs?cker, is attached to the Kaiser-Wilhelm-Institut in Berlin where some of the American work on uranium is now being repeated.
Yours very truly
Albert Einstein
總統先生：
最近，費米和西拉德兩位教授曾把他們的壹些研究報告，以手抄本的形式送交我們。這些報告使我們深信：不久的將來，鈾將成為壹種新的並且是極為重要的能源。根據目前某些方面的情況來看，我們政府應該在這方面及時警覺，同時，在必要時得采取迅速行動。因此，我認為有責任提醒您註意下列的壹些事實以及我的勸告。
在過去的四個月，由於法國的約裏奧·居裏和美國的費米及西拉德的努力，使得在大量的鈾中能夠引起壹種鏈式核反應，大有實現的希望。在這種反應中，能產生極大的能量，同時也會產生大量新的像鐳壹樣的放射性元素。現在我們幾乎可以確定，在不久的將來就能完成這種反應。
這種新現象同時也提示我們，可以制造壹種新型炸彈。雖然把握較小，但這種想法還是可信的。壹顆這樣的威力極大的新型炸彈，可用船舶將它運送到壹個港口，並予以引爆。它的力量足夠炸毀整個港口四周的壹些地區。然而，可惜的是這些炸彈的重量太大，不便於空中運輸。
在美國，僅有中等數量的貧鈾礦，在加拿大和捷克有稍好壹點的鈾礦，而最好的鈾礦是在剛果。
這樣看來，也許您會想到，政府行政機構與在美國致力於鏈式反應研究的科學家之間，最好能有壹些密切的聯系。要達到這種目的的可能辦法是您把這項任務委托給壹個您所信任的人，最好他沒有官員的身份，他的工作可以包括下列數項：
（1）接近政府各部門，使它們知道進壹步的研究發展，他對政府的決策提出建設性的意見，同時還要特別註意“維護鈾礦在美國的供應”。
（2）加速實驗工作，目前進行實驗工作的預算僅限於幾個大學的實驗室而已，為了加強實驗工作，我們可以準備基金（假使這筆基金的確需要的話）。通過這位工作人員的關系首先可以向壹些誌願負擔這筆費用的私人來借貸，其次我們爭取壹些工業實驗室的合作，這些實驗室都具有我們所需要的設備。
據我所知，德國人在事實上已經停止出售他們接管的捷克鈾礦開采出來的鈾。他們如此的早期行動，或者可被認為是由於德國副國務卿的兒子馮·韋斯裏克任職於柏林威廉皇家學院，而這個學院裏，和美國壹樣，鈾的研究工作，正在反復地進行著。
您的十分忠實的
阿爾伯特·愛因斯坦
羅斯福在白宮辦公室裏，默默地研究了愛因斯坦的信，開始感到舉棋不定。但當他想到德國正在加緊研制原子彈時，就暗暗下了決心。經過壹星期的全面考慮，他對來信作了肯定的回答，並發出了進行核試驗研究的指令。
不知道完不完整.