MINOT AIR FORCE BASE, N.D. (AP) — Defense Secretary Jim Mattis said Wednesday he has become convinced that the United States must keep all three parts of its nuclear force, rather than eliminate one, as he once suggested.

Some argue that ground-based missiles may no longer be necessary to America's policy of deterrence, and the Trump administration has been reviewing the military's nuclear posture.

Mattis has called the submarine-based component "sacrosanct" and has said it is necessary to retain the ability to fire nuclear weapons from planes.

Together, those three prongs constitute what the...