These brass are simply trying to justify more defense spending with their pseudoscientific hoo-hah.  NK doesn't have a miniaturized warhead yet, nor is their Hawaii-capable ICBM anything like a reality.  Gotta have both before they become a serious threat, and that's at least a decade away or more -- because the difficulty curve only gets steeper from where they are now, particularly with sanctions.

Besides, any attack will come not from an ICBM but a sub-launched cruise missile a handful of miles offshore.  No warning interval and no defense.

Mind you, O'ahu is certainly a fat target.  But talking about buildings with thick concrete walls as effective fallout shelters is also hoo-hah.  Without proper air filtration systems, generators and fuel supplies, etc. etc,, the food, water and sanitation are a short-term joke that will only delay the inevitable -- and not for very long.   Half a kiloton?  8k casualties?  Yeah, right.  A real bomb will leave 500k dead on O'ahu. Ponder that.