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Because ABM-produced X rays and neutrons could sweep such large segments of the skies clear of threatening ICBMs, defense planners believe a relatively small number of Spartan missile batteries—costing a total of $4 billion—could defend the entire continental U.S. against the kind of primitive missile attack that China may well be able to launch by the mid-1970s. They could also provide protection against a few Soviet ICBMs that might be launched accidentally.
But even the installation of many Spartan batteries—backed up by smaller and faster Sprint missiles for short-range interception of ICBMs that penetrate the X-ray curtain—would not provide sufficient protection against a determined and massive attack by the Soviet Union. Using shielding, decoys, multiple and maneuverable warheads and radar-jamming chaff or nuclear explosions, the Russians could confuse and overwhelm U.S. defenses—just as the U.S. could overcome theirs.
* An ICBM two miles from the blast will receive only one-quarter of the X-ray energy that hits a missile one mile away. At a distance of three miles, the impacting X-ray energy will be only one-ninth as large.