A Continent is Bridged, 1940

This 1940 AT&T film opens with an engineer explaining telephony basics—repeaters, amplifiers, loading coils—to a bowler-hatted visitor in a grand office. In sharp black-and-white or early color, it zooms into a “Repeater Development” door, overlaying lab folders on circuits and vacuum tubes, then pans over formula-strewn papers. A reenactment of the 1915 transcontinental line’s completion follows: men raise poles across deserts, plant a San Francisco-New York sign, and wave an American flag, uniting a nation by wire.