American citizens who were convicted of spying on behalf of the Soviet Union. The couple was accused of providing top-secret information about radar, sonar, jet propulsion engines, and valuable nuclear weapon designs; at that time the United States was the only country in the world with nuclear weapons. Convicted of espionage in 1951, they were executed by the federal government of the United States in 1953 in the Sing Sing correctional facility in Ossining, New York. Their sentences (especially Ethel's) were felt to be unjust by many people all over the world including luminaries such as Frida Kahlo, Dashiell Hammett, Albert Einstein, Pablo Picasso, Jean-Paul Sartre and Pope Pius XII. Protests were held. President Eisenhower let the sentence stand and they were both executed.