British Editions

From the back cover of the 1971 Arrow edition

The three guerillas made a raid for food and supplies. The defenders kept them off with lasers. So they used the stranse new weapons that they. had found. The illusion "machines. ,They worked well. Twenty-four phantom men who fought like veterans, helped to carry the captured supplies into the mountains.
Later they conjured up a complete army of illusions: ~iant vampires. man-eating plants, Valkyries, cannibal children.

The trouble was, when they switched off the machines: the phantoms didn't goaway....

From the back cover of the 1987 Arrow edition

Earth has been taken over by a strange a lien force - creatures whose instinct for survival overrides any human resistance. Then a vital weapon - with the power of electronically warping the mind-falls into the hands of a terrori st grou p still strong enoug h to oppose the a I iens. A weapon so powerful that it cannot be controlled. The control of Earth is in the balance- and the balance is a terrifyingly precarious one.