A severe electromagnetic threat is caused by the detonation of nuclear devices. Such explosions generate photons (gamma rays) which through the Compton Effect produce fast electrons forming the source currents for intense electromagnetic fields.

Typical E-fields are unidirectional pulses with a rise-time of a few nanoseconds, decay time of the order 1us, with a peak amplitude of 50kV/s or so. This threat is important when considering the hardening of military systems and some important civilian systems (eg communications facilities).