On this day in 1953, Julius and Ethel Rosenberg were executed for conspiracy to commit espionage for their part in helping the Soviet Union develop a plutonium implosion device like this one.
Fat Man Blueprints
Ironically, the pro-communist German scientist, Klaus Fuchs, did much more to assist the Soviets with their nuclear program than the Rosenbergs, but he was not executed. I wonder... if the Rosenbergs had been German, like the Red Fox, rather than Jewish, would they have been executed? I doubt it.