The rapid evolution of radio and radar systems for military use during World War II, and devices to counter them, led to a technological battle that neither the Axis nor the Allied powers could afford to lose. The result was a continual series of thrusts, parries, and counter-thrusts, as first one side then the other sought to wrest the initiative in the struggle to control the ether. This was a battle fought with strange-sounding weapons-"Freya," "Mandrel," "Boozer," and "Window"-and characterized by the bravery, self-sacrifice, and skill of those who took part in it. During the war, however, and for many years after, electronic-warfare systems and their employment during the conflict remained closely guarded military secrets. When that veil of secrecy was finally lifted, the technicalities of the subject helped ensure that it remained beyond the reach of many lay researchers and readers.Long regarded as a standard reference work, Instruments of Darkness has been expanded and completely revised.