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From Atkinson’s The Guns at Last Light

A GI shivering in an Ardennes foxhole asked, after his first glimpse of a German Me-262 jet streaking overhead, “How come we don’t ever have any secret weapon?” Yet thousands of enemy troops now sensed what many American soldiers still did not know: that a secret weapon no bigger than a radio tube was being used in ground combat for the first time across the Bulge, enhancing the killing power of U.S. Artillery with what one enthusiast would call “the most remarkable scientific achievement of the war” except for the atomic bomb.

The new weapon’s origin dated to 1940, with a recognition that on average 2,500 antiaircraft artillery shells would be needed to bring down a single enemy plane. Both field artillery antiaircraft rounds exploded either on contact or when a fuze detonated the shell after a preset flight time; neither technique offered killing precision. Scientists and engineers instead sought a fuze that could sense proximity to the target, causing a shell to blow up not when it randomly reached an altitude of ten or fifteen thousand feet, but rather when it detected an airplane within the kill radius of exploding fragments. Such a fuze would have to withstand the stupendous strain of cannonading, including a g-force of twenty thousand upon leaving a gun muzzle and the centrifugal forces of a shell spinning at five hundred rotations per second. It would also have to be simple enough the build by the millions on an assemble line, and sufficiently miniaturized to squeeze into a shell nose roughly the size of an ice cream cone.

The resulting device, eventually known by the code designations “VT” or “T-98,” and by the code name “pozit,” contained a tiny radio transmitter, which broadcast a signal in flight. When the beam bounced off a solid object, a receiver in the fuze detected the reflected signal and tripped a firing circuit that detonated the shell. A 5-inch pozit shell, fired by the USS Helena in the South Pacific, had for the first time brought down a Japanese plane in January 1943. But for eighteen months the fuze could be used only over water or friendly territory, for fear that if the enemy retrieved a dud, Axis engineers could copy the design. Pozit shells were secretly used against V-1s aimed at London-British officials considered them up to five times more effective than time-fuzed rounds-and to defend Cherbourg harbor and the Mulberries off Normandy. More recently, British Lancaster bombers had flown and emergency consignment of pozit fuzes from a Cincinnati plant to Antwerp for use against German flying bombs.

Pozit variants had been developed for the field artillery, using radio signals bounced off the approaching ground to detonate shells fifty or seventy-five feet up. Experiments in North Carolina showed that regardless of terrain, weather, or darkness, even entrenched targets were highly vulnerable to a lethal spray of steel shards from such airbursts. One senior Army general called it “the most important new development in the ammunition field since the introduction of high explosive projectiles.”

With approval from the Charlie-charlies, SHAEF in lat fall fixed Christmas as the day gunners in Europe could open fire with pozit shells. More than a thousand commanders and staff officers were briefed on the secret, with firing demonstrations in six Allied armies. Hitler hastened the day: when HERBSTNEBEL began. Eisenhower moved up the release by a week. A gunner in the 99th Division described “piles of shells with many men using wrenches and hammers to bang off the one [fuze] and install the other.” Withing days of the first use by field artillerymen, reports described “the slaughter of enemy concentrations east of Bastogne and interdictions of the principle enemy supply routes west of St. Vith. “Twelfth Army Group cheerfully reported that the pozit fuze “is a terror weapon.” SHAEF concluded the “the enemy has been severely upset.

Three hundred American companies would soon mass produce nearly two million fuzes a month at $20 each. “The new shell with the funny fuze is devastating,” Patton wrote the Army ordnance chief in late December. “The other night we caught a German battalion, which was trying to cross the Sauer River, with a battalion concentration and killed by actual count 702.” Such exaggerations-and Patton’s tally’s often proved inflated-were common, and many unsubstantiated claims of pozit lethality would emerge from the Bulge. In the event, fewer than 200,000 pozit rounds were fired by 12th Army Group in the Battle of the Bulge: a modest fraction of the total, although it did include one-quarter of the Army’s heaviest shells. Nor was the new technology flawless. Tall trees, chimneys, steeples and straying spotter planes could cause premature detonations.

Yet the pozit would prove as demoralizing to German troops as it was heartening to GIs. Some enemy officers called it the “electro shell” or “magnetic igniter,” believing that terrestrial magnetism triggered the fuze. “It hangs in the air until it finds just the right place to explode,” one captured soldier insisted. Shell fragments were said to slice through thick logs atop enemy bunkers, and a single 155mm airburst reportedly could shred every square foot within a seventy five-yard diameter. Such mayhem was “pure manslaughter,” another German prisoner complained. “The devil himself could not escape.”