Early WW II: Pearl Harbor was under repair from attacks on the previous December, and the only imminent attack expected was in the Philippines, about as far as one could get from the East Coast. But war officials were not taking chances. After a German submarine was found (and destroyed) off the U.S. eastern coast, the government ordered a “dim-out” to prevent the detection of American ships near the coast. Ships were ordered to run dimmed-out, too, so as to be better blend in with the darkness out at sea and escape submarine attacks, but even an small light thrown from a coastal boardwalk could have been enough to sink a ship.

On this day, April 28, 1942, the dim-out went from an occasional to a nightly occurrence, as everything from residential buildings, to theatre signs, to car headlights were ordered shut off for the night hours.

No country took wartime blackouts more seriously than the British. Their factories that needed to keep working through the night hours had to install blackout paneling or just black paint over any surface through which light could escape. Double doors, similar to those in photographer darkrooms, were installed in many public institutions to prevent people lighting up during entrances and exits. Violators faced hefty fines.