A few Americans have been conscientious objectors (COs) in every one of America's wars. But World War II, the "Good War", posed a special problem for men of conscience. Out of 16 million called to serve in the armed forces, only 42,000 refused to participate in the killing due to religious, moral, philosophical, or political convictions. But rarely for lack of courage: 25,000 served as military noncombatants, often in war zones. Some volunteered for dangerous medical experiments, enduring starvation diets and inoculation with live hepatitis virus. About 3,000 others staffed mental hospitals. Their efforts to change the horrible conditions they found led to lasting reform in the care of the mentally ill. Over 7,000 men refused any alternative service on principle and went to prison. After the war was over, COs continued to work for social and political causes. They helped to relieve the suffering of war survivors by taking the place of soldiers returning from Europe and Asia. Former COs became leaders in the American civil rights movement, the fight to end South African apartheid, and resistance to the Vietnam War.