Missiles. The striking power of the Air Force has been further strengthened by the addition of missiles. Of particular significance has been the development of the intercontinental ballistic missile (ICBM). A breakthrough in thermonuclear research in 1952-53 made it possible to build smaller atomic warheads, and led to the decision to develop the ICBM. The highest national priority was assigned to the program, for which the sole responsibility for development and eventual operation was given to the Air Force. The Atlas and the Titan, two ICBM's of alternate configurations designed to travel 5,500 miles, were placed on accelerated development schedules. The Atlas had its first successful test launching in 1957, at which time the Titan had reached the static testing stage. In the field of intermediate range ballistic missiles (IRBM), the Air Force Thor and the Army Jupiter, both of 1,500-mile range, were ordered into production during 1957. The Snark, an air-breathing missile, was placed in production, and the first of these missiles were in service use by the end of 1957. It has a speed of 600-700 miles per hour and is highly accurate and fully operational. Among the Air Force's other nonballistic missiles, either in production or in operation, are: the Falcon, Genie, and Rascal (air-to-air); the Bomarc (surface-toair); and the Matador (surface-to-surface).

Air Defense. When the Soviet Union exploded an atomic device in 1949, it underscored the need for an effective round-the-clock system of air defense of North America, including not only manned interceptors and antiaircraft weapons but also a continent-wide electronic warning system. By 1953 a net of 75 radar stations was in operation. However, the system was still defective. As a gap-filler program, beginning in 1954, the Air Force placed over 300 small automatic radar sets between the larger radar stations. Meantime, following negotiations between the United States and Canada, a chain of radar stations across southern Canada, known as the Pinetree Line, was jointly undertaken and completed by the end of 1955.

This was a beginning; but the need

increased for a continental warning and control system that would provide at least two hours' notice of an enemy bomber attack. To this end the United States and Canada agreed in 1953-54 to build two additional lines of radar. The Mid-Canada Line was installed by Canada along the 55th parallel; it was completed in 1957. The Distant Early Warning Line or "DEW Line," lying along the 69th parallel (inside the Arctic Circle) and extending 3,000 miles from the east coast of Greenland to northern Alaska and the Aleutian Islands, was started by the United States early in 1955. Completed DEW Line facilities, costing $500,000,000, went into operation under the Air Force in August 1957.

Additional air defense measures include manned interceptors for the Air Defense Command; U. S. Army missiles for close-in defense; U. S. Navy radar picket ships; airborne early warning and control planes, and "Texas Towers," which are fixed radar stations built 100 miles out to sea on the continental shelf."

Another important contribution to air defense was begun in 1955 when basic planning for the SAGE (SemiAutomatic Ground Environment) system was completed, and construction of technical facilities begun. When it is completed, SAGE will provide a system of complicated electronic "brain" devices that gather information from several points, simultaneously furnish data needed for the solution of complex air defense problems, and provide radarscope views of an air battle within a geographical area.

Still another startling innovation in communications, and hence in the improvement of the air defense complex, was the perfecting of the "White Alice" communications system. This employs a network of unorthodox-looking convex steel screens 60 feet high and weighing 100 tons each, which serve as directional transmitting antennae to focus a powerful radio signal, much as the curved mirror of a searchlight focuses candlepower. Just as the searchlight beam may be seen by a distant watcher, so the faintest portion of a radio beam is detected far beyond the horizon by a relay station, then amplified and trans

For further data on Army contributions to continental defense against air attack, see chapter 3.