The famous Einstein–Szilárd letter, sent to President Franklin D. Roosevelt on August 2, 1939:
It was drafted primarily by Hungarian physicist Leo Szilárd (with contributions from Eugene Wigner and Edward Teller), and signed by Albert Einstein because his name carried the greatest weight in public and political circles. The letter warned of the potential for nuclear fission to release enormous energy and urged the U.S. government to begin serious research into atomic weapons before Nazi Germany could develop them.
Here is the full text of the letter (transcribed exactly as it was sent):
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 almost certain – 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 now 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 this situation you may think it desirable to have some 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 a private person 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 Weizsäcker, is attached to the Kaiser-Wilhelm-Institut in Berlin where some of the American work on uranium is now being repeated.
Yours very truly,
(signed)
Albert Einstein
Historical Context and Significance
- Timing: Written just weeks before Germany invaded Poland (September 1, 1939), marking the start of World War II.
- Delivery: The letter was hand-delivered to Roosevelt by Alexander Sachs on October 11, 1939 (Einstein did not meet Roosevelt personally).
- Immediate Outcome: Roosevelt responded by forming the Advisory Committee on Uranium (October 21, 1939), which later evolved into the Manhattan Project after Pearl Harbor and after further pressure from scientists (including the 1941 MAUD Committee report from Britain confirming chain-reaction feasibility).
- Long-term Impact: The letter is widely credited as one of the key triggers that led to the U.S. atomic bomb program, culminating in the bombings of Hiroshima and Nagasaki in August 1945.
Einstein’s Later Regret
Einstein himself later expressed deep regret over signing the letter. In a 1947 interview he said:
“Had I known that the Germans would not succeed in developing an atomic bomb, I would have done nothing.”
In a 1954 letter he called the atomic bomb “the greatest disaster to befall mankind,” and he became a strong advocate for nuclear disarmament and international control of atomic energy.
Summary of the Letter’s Core Warning
The letter warned that nuclear fission (recently discovered by Otto Hahn and Fritz Strassmann in 1938, and explained by Lise Meitner and Otto Frisch) could lead to:
- a self-sustaining chain reaction releasing vast energy (power source).
- the possibility of extremely powerful bombs (weapon).
It urged government action to secure uranium supplies and accelerate research before Nazi Germany could weaponize the discovery.
This letter remains one of the most consequential scientific communications in history, marking the moment when the scientific community formally alerted political leadership to the terrifying military potential of nuclear energy.