WASHINGTON –  Wounded in both legs and wearing a U.S. Army field coat peppered with bullet holes, 1st Lt. Robert Schmitt led a desperate U.S. hilltop assault against advancing Chinese forces in one of the bloodiest battles of the Korean War. He never returned.

The hunt for thousands of fallen American troops like Schmitt, missing from a conflict fought six decades ago, is about to resume in North Korea as tensions ease between the wartime enemies.

A decade of search operations that led to the recovery and identification of 92 troops was suspended seven years ago, with the U.S. citing worries about the security of its personnel. That ended the only cooperation between the militaries of the two nations, which formally remain at war because the 1950-53 conflict ended with a cease-fire and armistice, not a formal peace treaty....