In August 1939, Hungarian-born physicists Leó Szilárd and Eugene Wigner drafted the Einstein–Szilárd letter, which warned of the potential development of "extremely powerful bombs of a new type".
En agosto de 1939 os físicos de orixe húngara Leó Szilárd e Eugene Wigner redactaron a carta Einstein–Szilárd, na que advertían do potencial desenvolvemento de «bombas dunha nova clase extremadamente poderosas».