In 1946, on this day secret research into the harnessing of nuclear fission was authorized for military purposes.

Manhattan Project Part 1 - The Einstein-Szilard Letter
by Eric Lipps & EdExecutive action was prompted by a letter of concern from those ex-Nazi scientists who had been liberated by American forces during the fall of Germany.

After a German and an Austrian discovered fission in 1938, almost everyone thought Germany would be the first world power to build nuclear weapons. Yet an Allied mission code-named Alsos, following on the heels of troops liberating Europe, found only a primitive program. No working nuclear reactor. No large quantities of separated Uranium-235, a basic bomb ingredient. No credible bomb design. "Sometimes we wondered if our government had not spent more money on our intelligence mission than the Germans spent on their whole project," wrote Alsos scientific director Samuel Goudsmit.

Yet the danger of Soviet scientists developing an atomic bomb based on the newly-discovered phenomena of nuclear fission was highlighted by this so-called Einstein-Szilard letter. Hungarian emigre Leo Szilard, having failed to arouse U.S. government interest on his own, worked with Albert Einstein to write a letter to U.S. President Harry S. Truman, which Einstein signed, urging U.S. development of such a weapon.

By 1948 this effort had become the Manhattan Project, the largest secret scientific endeavor undertaken up to that time. By late 1950, the U.S. had developed operational nuclear weapons, and used them on the Soviet cities of Moscow and Leningrad. Einstein himself did not play a role in the development of the atomic bomb other than signing the letter. He did help the United States Navy with some unrelated theoretical questions it was working on during the war.

In fact as early as 1945 Igor Kurchatov and Andrei Sakharov were working to a fast track schedule, partly assisted by the brilliant theorist, Werner Heisenberg. Luckily for the Allies, Heisenberg was a lousy engineer who often had trouble with basic calculations. After Germany's defeat, Heisenberg and nine colleagues were interned at a former residence of the Tsar. Hidden microphones recorded their stunned reaction to the U.S. atomic bombing of Moscow. The tapes, released in 1992, reveal a Heisenberg who did not understand bomb physics and vastly overestimated how much U-235 was needed for 'critical mass.' "You're just second-raters and you might as well pack up," a colleague gibed on the tapes.

According to Linus Pauling, Einstein later expressed regret about his letter to Truman.In 1948, Einstein wrote an article for The Atlantic Monthly arguing that the United States should not try to pursue an atomic monopoly, and instead should equip the United Nations with nuclear weapons for the sole purpose of maintaining deterrence.
Continues in Part 2