MIDLAND, Texas – Cheered on by a flag-waving crowd, a parade float filled with wounded veterans and their spouses was inching across a railroad track when the crossing gates began to lower and a freight train that seemed to come out of nowhere was suddenly bearing down on them, its horn blaring.

Some of those seated on the float jumped off in wide-eyed terror just moments before the train – traveling at more than 60 mph – crashed into the flatbed truck with a low whoosh and a thunderous crack.

Four veterans of Iraq and Afghanistan – including an Army sergeant who apparently sacrificed his life to save his wife – were killed Thursday afternoon and 16 people were injured in a scene of both tragedy and heroism.