civil defense, nonmilitary activities designed to protect civilians and their property from enemy actions in time of war. A civil defense program usually includes measures taken during peace (e.g., building home shelters or air raid warning practice), measures to warn civilians of an impending attack, to protect them during attack, and to save their lives and property after attack. Civil defense grew in proportion to the use of aircraft in modern warfare, becoming significant during World War II, when both sides engaged in the strategic bombing of civilian populations. After World War II the existence of nuclear weapons, the development of long-range bombers and missiles, and the ever-present possibility of war encouraged the establishment of comprehensive civil defense systems. The principal U.S. civil defense agency was established by executive order in 1950, and in 1961 civil defense functions were transferred to the Defense Dept. Opinion in the United States has traditionally been divided over the value of civil defense programs. Opponents of civil defense have maintained that, given the destructiveness of modern weapons, warning and shelter systems are useless and merely encourage war hysteria. Proponents of civil defense have asserted that, since a major danger from a nuclear attack is radioactive fallout, an adequate shelter program can save the lives of a large portion of the population. After the beginnings of a détente with the Soviet Union and the People's Republic of China in the 1970s, interest in civil defense in the United States, which peaked at the height of the cold war, began to decline; that decline was furthered by the break up of the Soviet empire. However, most industrialized countries still maintain some form of civil defense.