Radio: Ether's Ack-Ack

With the dogged persistence of antiaircraft batteries blazing away at attacking bombers, Axis radio transmitters are fighting off United Nations' broadcasts with strange and unpleasant noises. When World War II began, Nazi jamming was unpredictable. Today Germany, Italy and Japan all jam regularly, systematically, most of the time.* In spite of their efforts, their jamming is far from 100% effective. The jammer's basic difficulty is that a determined listener can follow a speaker's voice through almost any kind of a din, can grasp the gist of a message even though he hears only a word here & there.

In principle, jamming is...