Not only would everything be devastated in the immediate vicinity of the blast but an EMP (electromagnetic pulse) could wipe out almost anything that uses electricity (including cars and battery-powered phones, radios, and flashlights) throughout a much wider area.
Unfortunately, the lack of U.S. nuclear testing since 1992 has also contributed to uncertainty about the adequacy of steps to protect conventional military gear from the effects of high-energy, electromagnetic pulse(EMP) attacks.