They have long since outlived their design life and for at least 18 years none of them has been tested in an operationally realistic way (that is, with an underground nuclear detonation).

CENTERFORSECURITYPOLICY: Stopping START

SEOUL, South Korea (AP) Even before she takes office Monday as South Korea's first female president, Park Geun-hye's campaign vow to soften Seoul's current hard-line approach to rival North Korea is being tested by Pyongyang's recent underground nuclear detonation.

NPR: SKorea's New Leader Faces NKorea Nuke Crisis

In February, the country conducted its third underground detonation of a nuclear device, possibly using enriched uranium rather than the plutonium employed in previous tests.

FORBES: Can U.S. Defenses Cope With North Korea's Missiles?