Americans Julius and Ethel Rosenberg (pictured) were executed as spies for passing nuclear weapons secrets to the Soviet Union.

Julius Rosenberg and Ethel Rosenberg were an American married couple who were convicted of spying for the Soviet Union, including providing top-secret information about American radar, sonar, jet propulsion engines, and nuclear weapon designs. Convicted of espionage in 1951, they were executed by the federal government of the United States in 1953 using New York's state execution chamber in Sing Sing in Ossining, New York, becoming the first American civilians to be executed for such charges and the first to be executed during peacetime. Other convicted co-conspirators were sentenced to prison, including Ethel's brother, David Greenglass, Harry Gold, and Morton Sobell. Klaus Fuchs, a German scientist working at the Los Alamos Laboratory, was convicted in the United Kingdom. For decades, many people, including the Rosenbergs' sons, have maintained that Ethel was innocent of spying and have sought an exoneration on her behalf from multiple U.S. presidents.

A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either nuclear fission or a combination of fission and nuclear fusion reactions, producing a nuclear explosion. Both bomb types release large quantities of energy from relatively small amounts of matter.