Counter-measures

When a modern bomber strikes into hostile air, it will carry few guns or defensive rockets--perhaps none. Its best defense against missiles and interceptors will be the countermeasures expert, who does his fighting with electronic bullets. In Aviation Week, Philip J. Klass tells a small part of the large, top-secret story of electronic countermeasures.

The simplest countermeasure, says Klass, is radio jamming that drowns out enemy radar or communications by brute electronic force. This sort of thing is now considered as crude as bayonet fighting. The modern objective is to blind the enemy, make him see double or lead him astray, preferably without letting him know that anything is amiss.

Subs & Ferrets. First step is to learn as much as possible about the enemy's equipment. This is done by submarines and "ferret" planes that eavesdrop on enemy radars and try to record the electronic voices of interceptors and guided missiles. Every shred of information is analyzed, including false information, and a fair idea of the enemy's electronics is built up.

Next step is to devise equipment that will cope in some way with the enemy's latest dodges. About the oldest passive electronic defense is "chaff"* strips of aluminum foil tossed from an airplane to give a reflection that an enemy radar mistakes for another airplane. This worked fine with the comparatively slow bombers of World War II, but the wind-drifted puffs of chaff are too easy to distinguish from fast-flying modern bombers. A promising improvement is to fire rockets loaded with chaff ahead of the bomber as a sort of smoke screen.

More interesting are active countermeasures, most of which depend on one of radar's basic weaknesses. Radar sends out radio waves that "illuminate" the target just like the light from a searchlight. Then it listens for reflections of its own waves and uses their timing and direction to tell where the target is. If the target is a well-equipped airplane, its countermeasures expert knows when he is being illuminated, and he usually knows it long before the reflections from his airplane get strong enough to be detected by the radar.

Warned in advance, he can play many tricks on the radar. One trick is to analyze its waves and then broadcast stronger waves that are just like them. If these are properly timed, the radar that picks them up will see a target at the wrong distance, and it may send a flight of interceptors to shoot down a bomber that is not there.

Most radars can cope with this fairly simple trick, so well-furnished bombers will probably carry decoys to mislead sophisticated radars. When the bombers have been illuminated and are likely to be attacked, they will launch small, fast missiles with transmitters that have been tuned to copy the reflected signals of the enemy's radar or with radar-reflecting devices that make them look bigger than they are. Such a decoy is hard to distinguish from a real bomber, and an attacking interceptor or missile is apt to "lock onto" it and let the bomber escape. Nature thought of this trick long before man did. Many lizards shed their tails when they are hotly pursued. The pursuer captures only the tail; the rest of the lizard escapes and grows another tail.

Code & Flares. All such tricks and more have long been familiar to every military nation, and many cycles of subtlety have been built upon them. Modern radars change their frequencies quickly and also change the length and shape of the pulses they send out. This amounts to a sort of code that the enemy must break, and often he has no time to do it. If he is attacked by a radar-guided missile, he may have only a few seconds to mimic its voice and prompt it to swerve aside into empty air.

When it looks as if a potential enemy has developed quick, automatic devices for breaking a radar's code, more complicated electronic codes must be devised. Some missiles have abandoned radar in favor of heat-sensitive eyes that guide them to the hot tail pipes of an enemy airplane. One answer to this dodge is to release decoys with powerful flares to attract the missile.

Electronic countermeasures have become so vital that many bombers will carry nothing but electronic equipment. Sylvania Electric Products Inc., for instance, is developing a special counter-measures pod to be. carried by a B58 instead of a bomb load or air-to-ground missiles. One or more such B-58s will convoy bomb-armed bombers, shelter them under a canopy of deceitful signals, tell attacking missiles to go away, and, as a last resort, surround the formation with a swarm of small, big-looking decoys.

* Originally called by the code name "Window," it was first used by the British in a big raid on Hamburg, July 24, 1943, when it completely confused the Germans' radars and paralyzed their air defense.

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