Kate Wagman
Kate Wagman voted up Korvo One's answer

During WWII Tesla offered the US gov a weapon which would stop any aircraft from flying over the borders, by burning out their electronics. The US  gov turned him down, but when he died (prior to the end of the war) his notebook containing this idea was lost. This is why everything about Tesla was … Read more

Kate Wagman
Kate Wagman voted up Rooster Cogburn's answer

This PDF is fairly long but well detailed. But you will get some answers other than a EMP device.

Electronic and Information Warfare