Late in a life lived unnervingly near the nuclear abyss, William J. Perry is on a mission to warn of a "real and growing danger" of nuclear doom.

The 88-year-old former defense secretary is troubled by the risks of catastrophe from the very weapons he helped develop decades ago.

Atop his worry list: a nuclear terror attack in a major U.S. city or a shooting war with Russia that, through miscalculation, turns nuclear.

He said in an interview that a terrorist attack using a nuclear bomb or improvised nuclear device could happen "any time now - next year or the year after."

Perry played a central role in developing and modernizing nuclear forces throughout the Cold War. He was a technology whiz-kid and later a three-time senior Pentagon executive.