American concerns over air defense of the continental United States were at their most grave in the 1950s. The descent into cold war in the late 1940s, the confrontation of two hostile political systems in distant Korea, and the Soviet development of atomic weapons earlier than expected by American military experts came together to stimulate popular pressures for a shield against manned bombers reaching the American heartland from the North Pole. The effect on the newly independent Air Force was significant-it required that the Air Force modify its weapons inventory, just as the service had settled on a strong strategic nuclear offensive force to deter an enemy attack. The new requirements for strategic defense threatened to compete heavily for resources with the Strategic Air Command, itself undergoing a buildup and the introduction of new airplanes and a ballistic missile force. The Air Force nevertheless soon realized that the prospect of an attack by bombers armed with nuclear weapons was real. At least a rudimentary defense system, one capable of growing in strength and sophistication as demands dictated, would be needed to persuade the Soviets that an attack might not succeed. The postwar Air Defense Command, an administrative and planning backwater compared to the Strategic Air Command, suddenly assumed far greater significance, absorbing a larger portion of the defense budget. The expansion of the air defense effort after the mid-1950s had an impact on service roles, forcing the Air Force to consider issues it had not addressed in the past. An effective guided missile defense in the latter part of the decade brought the U.S. Army into the Continental Air Defense Command. Continental implications of the defense problem went beyond dividing responsibilities for tracking and destroying incoming attackers. A wide range of international political issues attended the emplacement of a defensive warning system, for much of its construction had to be on Canadian soil. Even here, the Air Force willingly proceeded, convinced that early warnings of an attack received from the net deployed in arctic regions would improve the survivability of the SAC force that would launch the counterblow.