Ulam worked with Edward Teller on the Manhattan Project. He found that Teller’s “Super” bomb design was unworkable, so they co-created the Teller-Ulam Design, which is the basis for all thermonuclear weapons.

After the Nazi rise to power, Szilard fled Germany for Britain and assisted refugee scholars in finding new jobs. Forseeing another European war, he moved to the US to work on creating a nuclear chain reaction. In 1939, he wrote the letter for Albert Einstein's signature that resulted in the Manhattan Project.

Frisch later collaborated with Rudolf Peierls to design the mechanism for the detonation of an atomic bomb in 1940. He was also involved with the Manhattan Proiect and conducted research in the Los Alamos Laboratory.

Meitner was praised by Albert Einstein as the "German Marie Curie".

She was the aunt of fellow physicist and collaborator Otto Robert Frisch, who was also Jewish.

Peirels came under scrutiny after Klaus Fuchs, a compatriot whom he had recruited to the Manhattan Project, was exposed as a Soviet spy in 1950. The scrutiny remained for many years, restricting Peierls' ability to operate as a scientist in America.

Wigner, along with Einstein, Szilard, Teller, and others, played a major role in advocating to the American government for the Manhattan Project, which developed nuclear weapons for use in WW2. From 1942 to 1945, he worked on the Manhattan Project at the University of Chicago.

In 1939, along with Szilard, Wigner, Teller, and others, Einstein worked to alert the American government of the necessity of developing atomic weapons in anticipation of a future conflict with Germany. They believed that Germany could win the race to the atomic bomb, and that "Hitler would be more than willing to resort to such a weapon."

Teller advised Israel on nuclear matters, and on the building of a hydrogen bomb in particular. He also persuaded the CIA to end attempts at inspecting the Negev Nuclear Research Center in Dimona.

After WWII, Oppenheimer became chairman of the General Advisory Committee of the newly created US Atomic Energy Commission. He lobbied for international control of nuclear power to avoid nuclear proliferation and escalation.

On August 29, 1939, Weizmann sent a letter to Neville Chamberlain stating in part: "I wish to confirm in the most explicit manner... that the Jews stand by Great Britain and will fight on the side of the democracies."