by JOSEPH TREVITHICK

In a famous scene from Alfred Hitchcock’s classic thriller Rear Window, injured photographer L.B. “Jeff” Jefferies tries to keep a murderer at bay by repeatedly blinding him with a camera flashbulb.

Whether or not the 1954 movie got them started, the U.S. Army once tried to turn the same basic idea into an actual weapon. During the Vietnam War, the U.S. Army’s Limited War Laboratory—a.k.a. LWL—in Maryland cooked up a so-called “ambush light” for American troops.

During a night-time ambush, the portable lamp would blind enemy forces and make them easier to see … and kill.

It might seem silly, but the project derived from the terrifying nature of infantry combat in Vietnam. The most terrifying form it took was the night-time ambush, where soldiers would spring a sudden attack on their enemies.

During such a surprise attack, ambushed soldiers could suffer extreme casualties in minutes or seconds. The almost pitch-black darkness added to the confusion and horror — even more frightening if the victims of the attack were caught in open terrain.

Thousands of Americans died in ambushes. But U.S. troops also became deadly professionals in the art, and deployed illumination to give themselves a killing edge.

“One of the essential requirements for a successful ambush is the element of complete surprise,” one LWL project report stated. “During night ambushes, success is enhanced if the surprise element is combined with simultaneous illumination.”

To see their enemies, American troops would shoot flares into the air, suddenly lighting up the battlefield. But this tactic would potentially reveal their own positions — spoiling the ambush.

Other times, American troops hid trip-wire flares. When Viet Cong guerrillas tripped the wires, the sudden flash of light would signal to the Americans where to shoot. But those signals weren’t always accurate.