WSJ’s Sune Engel Rasmussen is the first civilian to take part in this grueling training with a unit of American Green Berets.

For most of the 369th’s Black members, it would take years, even decades, to receive American military honors.

In March 1916, Americans living in the quiet town of Columbus, N.M., suddenly found themselves attacked by Mexican bandits, and many citizens sought to arm themselves and fight back, both during the ...