At its narrowest point, the English Channel separating the UK from France is only about 20 miles wide – but that was enough to save it from at least two empires bent on conquest – Napoleon’s France in the 18th century and Hitler’s Germany in the 1940s. Having taken control of all of Western Europe, Germany set their sights on England – but a sail across the channel would be foolhardy until Germany could get dominance of the skies. Britain had homefield advantage (it was not unheard of for shot-down British pilots parachuting safely down to London and catching a cab back to headquarters) but Germany had the superior air force. Still, Britain held fast, and Hitler, in frustration, changed strategy.

On this day, December 29, in 1940 Germany began using incendiary bombs in raids over London. Given that much of the city structures were still made of wood, this caused tremendous damage – but it failed, as Hitler hoped, to demoralize the population, and actually strengthened Britain’s defensive capability.

With the switch from the military to civilian targets, Britain was able to repair the factories and air defenses, making a German landing even more difficult. But the damage to London proper was great. Enrie Pyle, an American war correspondent described the scene after one such nighttime raid: “You have all seen big fires, but I doubt if you have ever seen the whole horizon of a city lined with great fires – scores of them, perhaps hundreds. There was something inspiring just in the awful savagery of it.”