In April 1970, 22-year-old James Speed Hensinger, an enlisted man in the U.S. Army’s 173rd Airborne Brigade, was stationed at a compound in Phu Tai, west of the coastal city of Qui Nhon, Vietnam.

Over the course of several nights, a lone Viet Cong fighter had repeatedly crept in among the rocks on a mountain overlooking the base and sprayed the camp with automatic AK-47 fire, perforating the sheet-metal roofs of the Americans’ hooches, killing one man and vexing the rest.

The soldiers were told that an overwhelming response would be prepared for the next time the “sniper” decided to strike.

Hensinger, sensing an opportunity, stuffed his Nikon camera, 50mm f/1.4 lens, and Ektachrome film (with a speed of ISO 64, usually used only in bright daylight) into the pocket of his fatigues. He timed his appearance for guard duty to make sure that he would be assigned to the watch tower with the widest view of the mountain and base.