The letter from Einstein to Roosevelt
In the United States, emigrant scholars decided to alert the U.S. administration. However, the perseverance of the Hungarian Jews Léo Szilard, Edward Teller and Eugene Wigner was needed to convince Einstein to sign the letter they had written in order to persuade President Franklin Roosevelt of the dangers of nuclear weapons on 2 August, 1939.
The following is a translated fragment from the Einstein-Szilard letter to Roosevelt: "... In the very near future, this new phenomenon (the chain reaction) could lead to the construction of a new type of bomb that is extremely powerful. A single bomb of this type, carried by boat and exploding in a port, might very well destroy the whole port, together with a part of the surrounding area... ".
Roosevelt's response, to Sachs Alexander, the President's Privy Councillor was: "We must act". After this statement, Einstein played no role in the atomic project, even though this energy came from his famous formula E = m.c². Roosevelt created the "Uranium Committee", equipped with a budget of 6,000 dollars in August 1939. The Italian physicist Fermi, a refugee, built a first prototype of a nuclear reactor, also called the "atomic battery" because it superimposed layers of graphite and uranium to test the chain reaction. Otto Frisch and Fritz Peierls demonstrated through calculation that a very small amount of uranium 235 could cause an explosion equivalent to several thousand tons of TNT (trinitrotoluene, the most powerful chemical explosive) in England, early 1941.
On 7 December 1941, the Japanese destroyed the U.S. fleet at Pearl Harbour; on 9 December, the United States joined the war; on 16 December, Roosevelt decided to equip the country with nuclear weapons. Huge resources were mobilised - the project would cost 2 billion dollars.