The early hours of June 13, 1944, were unseasonably cold.

In east London, on a high plateau south of the Thames, British firemen awoke in darkness to the sounds of air-raid sirens. They trudged from their watchmen’s hut and crossed the tarred parade ground and roadway toward the small, brick, concrete-roofed fire station of their army base. They were used to the sirens and knew the routine. But something that morning felt different.

Gunfire was echoing in the gloom, but it sounded distinct from the usual volleys. Normally Londoners could hear the deep booms of the 3.7-inch cannons that the anti-aircraft crews used to bring down the Luftwaffe bombers. But today the clatter was lighter, from 40-millimeter Bofors guns, suggesting a lower-flying target.

Searchlight beams crossed the low-hanging clouds. Locked briefly in a glowing ray, an enemy aircraft rushed by them “at incredible speed,” one fireman recalled. It was far faster than British Spitfires or even the Luftwaffe’s breakneck Messerschmitts. Crimson flames jetted from the clacking object.

Was it an ultra-fast German bomber executing a sneak attack? It soared over St. Paul’s Cathedral toward the heart of the city, and raced over the ships floating on the Thames, downstream of the Tower Bridge, where supplies were being loaded for France. Gunners on the armed ships opened fire with all they had, illuminating the dark early morning with tracer bullets—dashes drawn in space like so many bioluminescent discharges. West of the Isle of Dogs, above Rotherhithe, the flame from the back of the craft died, and the engine quieted. The firemen waited—it felt like an eternity—for the impact sound of the “crashing” pilot.

After hearing a distant explosion, they returned to sleep.

Witnesses who glimpsed the four Nazi aircraft that reached English soil that morning came to similar conclusions as the firemen. The objects looked like crippled planes. From below, observers saw “nothing but a black shape with sheets of flame spurting out behind it.” Dark silhouettes appeared over farms like burning black swords knifing through night.

It was not until a few days later, when 73 of them reached greater London, that citizens began to learn the truth of the German “buzz bombs.” They were V-1s, 4,900-pound winged missiles flying on autopilot. London newspapers announcing the arrival of “pilotless warplanes” assured readers, “Our scientists will defeat it.” The Evening Standard ran a column titled “How the Robot Works.” Another article, “How to Spot Ghost Planes,” detailed the craft’s telltale characteristics: its “terrific speed,” the flames from its exhaust, and its loud buzzing vibrations. The peculiar aircraft weren’t “crashing.” Their noisy engines were cutting out above the city, leaving the 1,800-pound warheads to drift down silently to their marks. “When the engine of the pilotless aircraft stops,” the Evening News advised, Londoners should take cover, as “it may mean that the explosion will soon follow—perhaps in five to 15 seconds.”

In the first two weeks of the siege, the German air force launched an estimated 1,585 drones, over 1,100 of which successfully crossed the Channel. British Royal Air Force pilots managed to shoot down only 315 of them. Five hundred and fifty-eight struck greater London.

Ack-ack guns, which usually defended the capital against Luftwaffe bombers, went silent. Shooting at the V-1s over the city, after all, could only succeed in bringing the pilotless aircraft down on their intended target. Gun sites went silent as flocks of noxious drones moaned and blustered, dove, exploded, and wrecked the city anew. After three weeks, Prime Minister Winston Churchill disclosed, the V-1s had claimed 2,752 lives and injured some 8,000, devastating figures not seen in London since the end of the Blitz three years prior.

The Allies’ anti-aircraft defenses hadn’t been useful then, either. In the early weeks of the Blitz, it had taken an average of 20,000 rounds from ack-ack cannons to drop a single German bomber. As one American physicist recalled: “It would be just a sheer stroke of luck to hit anything.” Now, once again, it was clear that the anti-aircraft battalions would stand little chance. Flying at over 400 miles per hour, the V-1s made for exceptionally fast targets. Even in locations where gun crews were cleared to fire, their speed made them difficult to track. According to one commander, the resultant shooting “was both wild and inaccurate.” British gunners were hitting only 9 percent of the drones.