More specifically, it would take out anything electronic. That means on the battlefield it would take out computers, GPS, targeting, etc. It would essentially level the playing field for an low-tech army. EMP is one of the big dangers of atomic weapons (outside of murder-death-kill) and according to some stories is the reason the soviets kept so much of their equipment at a low-tech level - so it would operate after EMP devastated higher-level electronics.
Thanks for the clarification.
I'm more fearful of the reality of an EMP vs Nuk capabilities