In March 2002, on a mountain near the Afghanistan-Pakistan border known as the Whale’s Back, a company from the vaunted U.S. 10th Mountain Division joined 400 Canadian troops and a handful of U.S. Navy Seals on an assault to clear enemy positions, bunkers and suspected cave complexes.

The undulating rock overlooked a valley through which Taliban and al-Qaida fighters were escaping into mountain passes that led them to safety in Pakistan’s hinterlands a few kilometres away...