Seven-League Maps

A great advance in wartime communication, already helping to clear the confusing Battle of the Mediterranean, was revealed last week in Electronics:

Flying over enemy territory, a reconnaissance observer spies, for example, an enemy force cunningly deployed to command a road below. The observer sketches the enemy position on a map, puts the sheet on a facsimile transmitter beside him. A few minutes later, at a U.S. base hundreds of miles away, the commanding officer pulls a sheet off a receiving machine, has a duplicate of the observer's drawing.

The observer sketches with a black pencil on a map printed in red. The transmitter, which is insensitive to red, sends only the black marks; consequently, if an enemy receiver intercepts the message, it shows only meaningless scrawls. But at headquarters the message is decoded by placing the transmitted sketch over a map duplicating the observer's.

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