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The EC-121 first pinpoints a radar site and then, by analyzing the signal picked up, determines just what that particular radar is used for. The experts can tell whether the radar under observation is meant to warn of possible threats from an enemy, whether it is intended to guide defensive surface-to-air missiles, or whether it is designed to control a network of offensive nuclear weapons. The aircraft's antennas, tuned to a wide range of radio frequencies used in military communications, can overhear conversations between major command posts 200 miles away and thus plot troop movements and combat readiness. Analysis of EC-121 data can reveal how much traffic is moving in and out of a military airfield.
One ingenious way to test a potential enemy's alertness is known as "exercising." That means feeding a fake signal back to the adversary's tracking radar at precisely timed intervals to simulate an intrusion in his airspace. The defender is lured into sending his interceptors aloft and activates all his secret radar equipment to bag this fictitious intruder. Meanwhile, from a distance, the spy plane can carefully monitor everything that is done by the enemy in order to meet the electronically manufactured threat. There is no indication, however, that the downed EC-121 was "exercising."
All this is part of U.S. intelligence gathering designed to prepare against any kind of military attack—for instance, a North Korean strike at South Korea. It also helps to keep the U.S. from getting caught in the kind of nuclear-blackmail situation that would have resulted had photo reconnaissance not turned up the Soviet IRBM installations in Cuba in 1962. Sophisticated electronic satellites have made some of the monitoring flights redundant, but the lumbering EC-121 is still more versatile and reliable, if more vulnerable to attack than a satellite orbiting in space.
The Soviets, naturally, have electronic spies of their own. Their trawler fleet makes up their most visible snooping force, showing up regularly in the South China Sea off Viet Nam and seaward from Cape Kennedy during U.S. space shots. The Soviets launch military reconnaissance satellites as regularly as does the U.S. TU-95 Bear turboprop converted bombers have been working near Alaska, since the early 1960s. Most recently they have been keeping tab on the U.S. Sixth Fleet in the Mediterranean—sometimes flying with Russian markings, sometimes with Egyptian. A shorter-range reconnaissance airplane, the TU-16 Badger, until a year aeo made frequent flights down the Pacific coast of Japan to spy on Japanese radar installations; it earned the nickname "Tokyo Express." But since the sort of military information that is secret in Communist countries is often openly available in the West, the Soviet Union generally has an easier espionage chore than the U.S.