Julius and Ethel Rosenburg

U.S. communists who were executed in 1953 for passing on nuclear secrets to the Soviet Union . During World War II, Julius obtained U.S. military secrets as an electrical engineer on defense projects; meanwhile, Ethel's brother, David Greenglass, gave the Rosenbergs nuclear data he obtained while working as a machinist on the atomic bomb project at Los Alamos , New Mexico . This information was turned over to Harry Gold, courier for the Soviets' U.S. espionage ring.

The Rosenbergs were arrested in 1950 after the discovery that another Harry Gold contact, Los Alamos physicist Klaus Fuchs, had delivered nuclear secrets to Moscow . The Rosenberg trial became a cause celebre among liberal activists and death penalty opponents, and debate still rages about the extent of their guilt. But a wealth of evidence, including some recently-released material, indicates Julius was in fact guilty as charged -- an enthusiastic Soviet spy, though perhaps not a terribly effective one. Ethel, though a devoted communist, may have been charged to bring pressure on Julius; her culpability remains a matter of more serious debate. The Rosenbergs were the first U.S. civilians to be executed for espionage.