First, the good news: Beijing is not building a microwave weapon to zap you into submission. Now, the bad: the Chinese are kind of interested in using electromagnetic radiation to fry your computers. Especially if you happen to live in Taiwan.

Those are the conclusions for a pair of secret reports, recently declassified and unearthed by the National Security Archive.

For years, a determined caucus of doomsayers in the U.S. have done their best to raise the alarm about the dangers of a king-sized electromagnetic pulse (EMP) wiping out American electronics. The result: a return, if not quite to...