In the 1940s, with the Second World War in full swing,
Japanese scientists sketched out a plan to build a microwave weapon to shoot
down enemy bombers. That idea, perhaps the earliest description of an
electromagnetic bomb, encapsulates much of what military officials still hope
to achieve with such weapons: disabling electronics (or, in some cases, people)
using a powerful energy beam, without causing any collateral physical damage.
The US military's attempts to make a practical weapon based on this idea have
so far resulted in only one system — at least as far as it has revealed
publicly. The Air Force has built the Active Denial System, a non-lethal
high-power microwave weapon supposedly able to deter an angry mob by creating
the sensation of being burned.