The top man at the Pentagon James Mattis visited Minot Air Force Base in North Dakota on Wednesday home to America's powerful nuclear arsenal.
The remote military facility houses more than 100 nuclear-tipped ICBMs, as well as nuclear-ready B-52 strategic bombers.
His visit comes less than two weeks after North Korea detonated its most powerful nuclear device to date.
While his trip was planned long before Pyongyang's recent string of military provocations, it gives Washington a chance to flex its own nuclear muscle.
Mattis had delivered a stark warning to the regime following its nuclear test, saying it would be met with a "massive military response" if threatened the U.S. or its allies.
The Pentagon chief also told reporters on Wednesday that the U.S. needs to maintain all three pillars of its nuclear triad, rather than phasing out one, as he had suggested in the past.
The nuclear triad refers to the three means at Washington's disposal of delivering nuclear weapons -- namely strategic bombers, land-based ICBMs, and submarine-launched ballistic missiles.
Some critics have argued, that ground-based missiles may no longer be necessary in maintaining America's nuclear deterrence.
In June, the U.S. inventory of Minuteman-III ICBMs was reduced by 50, for four-hundred missiles in total the lowest number since 1962.
Yu Joonhee, Arirang News.