With a new adaptation of black-light rays, United States Army trucks can be convoyed rapidly at night without the use of lights that might betray their presence to enemy planes overhead. Each truck has mounted at the back a greenish disk, barely noticeable, which glimmers in eerie fluorescence. Only the driver of the truck following can see the “invisible” disk, which glows vividly before his eyes as he sights it along a black-light beam emanating from a point near the windshield of his own truck. The leader of the procession finds his way with the aid of disks of a similar type, mounted on stakes, which are stuck into the ground along the route.