After trekking for five hours up steep Himalayan slopes, crossing numerous creeks and hacking a trail through bamboo forests, Clayton Kuhles and his guide reached the spot where a U.S. military plane had fallen more than six decades ago.

Out of breath and sweating, he rummaged through the forest-floor vegetation and excitedly pulled out rusted parts of an aircraft engine strewn atop a hill here in India's northeastern state of Arunachal Pradesh. His eyes scanned for clues as he sifted through the debris.