They were soldiers preparing to go to war, sometimes for the second or third time. They were also sons, daughters, fathers and a mother-to-be.

They were 21-year-old Jason Dean Hunt, who his sister said was proudest behind the wheel of his Bradley Armored Vehicle, from rural Oklahoma; Francheska Velez, 21, who was looking forward to the birth of her first child, from Chicago; and Amy Krueger, 29, a sports and outdoors enthusiast, from tiny Kiel, Wis.

These...