GRID: America's frail defense against a nuclear-tipped threat

The first major U.S. military attempt to explore electrical effects in the upper atmosphere was a brutal, secretive and unsettling affair. It came in 1962, with a hydrogen bomb test called Starfish Prime. The 1.4-megaton warhead detonated at 250 miles over the mid-Pacific Ocean, creating an electromagnetic pulse that blew out streetlights and shut down telephone systems in Hawaii, 898 miles away. Officials today warn that a U.S. enemy like North Korea could use an EMP to badly damage the U.S. grid.