According to the Department of Defense, the Air Force base is the only installation to have two legs of the nuclear triad: strategic bombers and intercontinental ballistic missiles.
He's reviewing and touring the US nuclear missile arsenal.
At Minot, Mattis toured a missile alert facility used to control ICBMs and a storage area where airmen maintain ICBM warheads.
Mattis said he has considered reworking the current nuclear posture known as the triad: nukes launched from USAF jets, USA navy submarines, or the ground. But he told reporters flying with him that his view has changed.
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"You want the enemy to look at it and say, this is impossible to take out in a first strike, and the [U.S.] retaliation is such that we don't want to do it", he said, according to AP.
Mattis's trip will also include a stop at U.S. Strategic Command in Omaha, Neb., the command in charge of nuclear forces.
The nuclear triad is the multi-tiered system that employs land-based nuclear missile silos, airborne nuclear-capable aircraft, and seaborne ballistic missile submarines to provide the USA military with strike capabilities anywhere in the world on short notice.
The Washington Post said that Mattis' remarks on the system known as the triad "came amid an ongoing review of the US nuclear weapons program and as tensions with North Korea remain high as that regime works toward developing a nuclear missile of its own".