Aug 4, 2020 7:00 AM

The American Scientists Who Saved London From Nazi Drones

For months, German V-1s terrorized the city. To take them down, US physicists had to develop a “smart fuse”—a task they were told was practically impossible.

Dr. Merle Tuve writes physics equations while a V1 flies above.

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.

Heavy guns were shoddy weapons in large part because of their “bullets.” At the time, rounds either had to hit a plane directly or be preset to detonate near an aircraft. The latter option was truly archaic. You had to estimate where a plane would be in say, 10 seconds, and then set the timer accordingly. Fire an instant too early or too late, and even if you aimed your gun nearly perfectly and grazed a target, rounds would explode thousands of feet away.

For some years, the solution had been obvious—in theory. If scientists could install some sort of sensor inside a round, it could be programmed to blow up in proximity to a plane. In effect, such a device would make an airplane look 50 times bigger to a gun. The problem was that the electronics of the era were extraordinarily delicate, and the pressure inside an anti-aircraft gun could reach up to 20,000 times the force of gravity. The task, in short, was to shrink components as delicate as old radio parts to the size of a tennis ball, cram them inside a bullet, and engineer this new “proximity fuse” to be rugged enough to work as it flew in the air more than 2,000 feet every second while spinning over 250 times.

For this to work, the new “smart” fuse would have to be both small and very sturdy—qualities that seemed to challenge the laws of physics. The task, American scientists were told, was practically impossible.

Years earlier, in 1940, four American physicists with zero background in designing weapons had taken up the challenge of developing the fuse at the request of the US Navy. The project was a true long shot. No one, not even their boss, the engineer Vannevar Bush, thought they would succeed. At first, they couldn’t buy an anti-aircraft gun or easily procure one from the Army or Navy. So the scientist built their own “cannon” out of Shelby steel tubing, a bored-out chunk of metal, and a spark plug. They needed “shells” for tests, so they made them from smaller pipes. They needed a firing range, so they set up an improvised proving ground on a friend’s farm in Virginia.

To buy gunpowder, they looked up “dynamite” in the yellow pages.

Led by a fiery physicist in Washington, DC, named Merle Tuve, the small band of four was organized under the umbrella of the National Defense Research Committee, which would become the research and development hub for new military devices. By the end of the war, Tuve’s staff would number over 1,000. They were known as Section T: T for Tuve. After the atomic bomb, their unlikely smart weapon would turn out to be, in the words of one prominent historian, “perhaps the most remarkable scientific achievement of the war.”

They raced to solve puzzle after puzzle as war raged.

By the end of 1940, Tuve’s group had studied the feasibility of different sensors: fuses that might trigger near the roar of an aircraft engine, or its heat, or a plane’s shadows or glare. The most promising design used a tiny radio device which could trigger if its own signal bounced back off a target. But any fuse was impossible without far tougher electronics.

Building miniature “rugged” batteries was no easy mission. Stacked battery cells of wet-paste electrolytes had to both power the fuse and fit into a space only 2 inches wide and 2.5 inches long, half the size of Eveready’s smallest batteries. For early firing tests, Section T froze larger batteries, sawed them in half, and sealed them in wax. But the most fragile components were the glass vacuum tubes needed as amplifiers (the transistor hadn’t yet been invented). The tubes, which resembled little light bulbs with delicate filaments, had to be smaller than paper clips. The only models tiny enough for the job were used in hearing aids.

To help strengthen the tubes, Tuve hired a 34-year-old assistant professor at Columbia University named Ray Mindlin. He had a taste for Chopin, dry humor, and sports cars. Mindlin was a specialist in materials science. Confident, stylish, with dark bushy eyebrows, he looked like the type of professor who engaged in profound discussions, in hallways, with his hands in his pockets. Asked how things were going, he would reply: “Fair to Mindlin.”

At first, the professor didn’t have security clearance. So Section T told him the tubes were meant for meteorological balloons and had to withstand a long fall to earth.

In early 1941, Mindlin devised a series of diagrams, “design curves,” that broke down how tough each tube part was. It wasn’t so different from how engineers approach bridge design. The tubes even had miniature cantilevers inside, like bridge supports. He worked out the warping and final “yield” points of dozens of minute components: grids, grid wires, and grid posts, getters, press-wire welds, and mica support spacers. He pored over blueprints of tube parts and compared yield points to the muzzle velocities of anti-aircraft guns.

The tube design that emerged was stacked, with platforms like floors in a high-rise that were strengthened by miniature columns. A wee spring, like a shock absorber, was added to the filaments. Mindlin didn’t seem to care how minute the amplifiers were. To him, these weren’t glass tubes the size of paper clips. They were narrow three-story buildings. Slowly, test by test, the little tubes began to grow stronger.

In early 1943, in the South Pacific, the US Navy began using Section T’s fuse against the Japanese air force. Over the course of that year, 75 percent of all rounds fired by their 5-inch guns used standard ammunition. Twenty-five percent used smart fuses—triggered by radio waves rebounding off enemy planes, they blew up within 70 feet of their targets and unleashed lethal barrages of shrapnel. Section T’s device was credited for 51 percent of downed planes. Twelve guns armed with the fuse were just as good as 36 guns that weren’t.

But the scientists were determined to improve the device. They erected a slew of buildings on a desolate tract southeast of Albuquerque, New Mexico, to use as a firing range. Stretched across dusty terrain between the Sandia and Manzano Mountains, the clandestine facility was longer than Manhattan and over twice as wide. Construction workers built bare-bones living quarters out of cinder blocks and paved 8 miles of road. Boundary warnings were posted across a 15-mile span. The station included a 1,700-gallon redwood water tank, a windmill to pump the well, storage sheds, and a shop building. There were corrals and a barn for the horses. Patrolling cowboys worked security in the barren foothills.

Blueprints of the Nazi V-1 arrived at the ranch on March 3, 1944, some three months before the drone would begin to terrorize London. The Allies weren’t exactly sure yet what the pilotless aircraft looked like, but from various intelligence sources, American engineers sketched out their best guess as to the weapon’s dimensions. Within two days, Merle Tuve’s scientists had assembled a full-scale model of the drone, covered it in chicken wire to reflect radio waves, and strung it up between the two towers. With only a 20-foot wingspan, it was much smaller than a normal aircraft—a little over half the width of a Japanese Zero. Gunners needed the most sensitive fuses available to ensure that rounds exploded at the ideal distance: within 25 feet. An analysis of the New Mexico tests concluded that if the anti-aircraft guns were accurate enough in their aim, the fuse had an 86 percent chance of knocking a V-1 out of the sky.

Within days, the test results were on their way to England.

By the middle of July 1944, more British citizens had been killed by German V-1s than had been lost over the first fifteen days of the Battle of Normandy.

Prime Minister Winston Churchill was holding meetings every other night with Royal Air Force leadership and General Frederick Pile, head of Anti-Aircraft Command. Pile argued forcefully that the existing defensive strategy against the V-1s wasn’t working. RAF airplanes, which still had first priority over the guns to police the skies and engage with the pilotless aircraft, were simply not gaining enough of an advantage over the Nazis’ terror weapons.

“All right,” Churchill replied, “from next Monday … General Pile is to have a free hand.”

Now, with General Pile in charge, the anti-aircraft guns would be relocated to the southern coast and given free rein to fire the smart fuse. Section T’s radio fuses had already begun to arrive in bulk in April. At Pile’s request, British gunnery instructors had been indoctrinated with the basics of the device. So had American anti-aircraft battalions stationed in England.

The coast of France was so close to one new American position that troops using binoculars could read the clock on the city hall tower of Calais.

“On a clear day,” said Ralph Griffin, an American gunner stationed near Dover, “we could see the Buzz Bombs almost as soon as they were launched.”

Under moonless, dark skies, night firing was an otherworldly event. At first, the pilotless aircraft appeared as mere “pin heads” glowing in the black, specks of fire groaning in the distance. At the sight of a V-1 quickening in the darkness, nervous gunners focused “on the little ball of fire.” The search beams locked onto V-1s, tips of guns flashed bright cotton-candy explosions, bursting flak flashed, and multicolored tracer bullets drew curved lines into the sky.

A V-1 warhead exploded by ack-ack fire would illuminate the night with a “terrific burst of yellow flame” followed by, after several seconds, a concussive blast wave that jarred the gunners, shook the earth, and whipped the tents.

At first, the American gunners found the V-1s to be maddeningly elusive targets. “But after we got proximity fuses,” one recalled, “we started to knock them down. We got to where we could get them if they were in range.”

Section T was on the coast also, training the gunners. One of Tuve’s friends, the physicist Ed Salant, arrived on July 30. He practically lived with the coastal batteries, motoring in an Army Jeep along narrow country roads in the blackout, scrambling between the gun sites.

In that first week after the guns had been shifted to the British coast, the percentage of V-1s shot down by Allied batteries had risen from 9 to 17 percent. Seventeen percent of V-1 “kills” then quickly grew to 24 percent. As the weeks passed, with the help of better radar and aiming devices, Section T’s smart fuse began to master the V-1.

Twenty-four percent became 46. Then the figure hit 67. Then 79.

Salant estimated that only 100 shells fitted with the fuse were needed, on average, to shoot a drone out of the sky—a figure five or six times better than standard fuses could deliver. General Pile noted that his best batteries were “getting one bomb for every 40 rounds.” Ten times better than regular fuses.

By September, the V-1 attack on England was effectively stopped.

“More was learned about the potentialities of anti-aircraft work in 80 days,” Pile recalled, “than had been learned in the previous 30 years.” He thanked Salant personally.

“Our reputation in the knowledgeable circles here is very high!” Salant wrote on September 5, 1944, in a letter back to Section T. “You can be sure that the [fuse] has saved the lives of thousands here. I do not believe we are through with the flying bomb, but I do not believe it will be a serious menace to London anymore.”

Londoners were “aware of danger,” Salant wrote, “but they were no longer oppressed by it.” Across the country, blackout restrictions, intended to hide English cities from Nazi bombers, were relaxed for the first time in years. Children, some too young to have ever seen working street lamps, gathered in the streets to see them illuminated.

Excerpted from 12 Seconds of Silence: How a Team of Inventors, Tinkerers, and Spies Took Down a Nazi Superweapon by Jamie Holmes to be published by Houghton Mifflin Harcourt on August 4, 2020. Copyright © 2020 by Jamie Holmes. Used by permission.

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