Eighty-five years ago this month, the December 1940 issue of Practical Mechanics had this illustration of the barrage balloons that were a familiar sight over London. My mid-1940, about 1400 such balloons had been deployed there and in other British cities. Each was tethered to a truck. They carried a steel cable to make navigation at lower altitudes dangerous or impossible. Enemy bombers were forced to higher altitudes. This made them more vulnerable to anti-aircraft fire, since the relative motion, as seen from the ground, would be much slower than a plane zooming by at ground level.