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 weapons?” Yet thousands of enemy troops now sensed what many American soldiers still did not know: that a secret weapon 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” besides the atomic bomb.
The new weapon’s origin dated to 1940 and the recognition that on average 2,500 antiaircraft artillery shells would be needed to bring down a single enemy plane. Both field artillery and antiaircraft rounds exploded either on contact or when a fuse detonated the shell after a preset flight time; neither technique offered killing precision. Scientists and engineers instead sought a fuse 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 its exploding fragments. Such a fuse would have to be simple enough to build by the millions on an assembly line and sufficiently miniaturized to squeeze into a shell nose roughly the size of an ice-cream cone.
A German Messerschmitt Swallow
The resulting device, no bigger than a radio tube, was eventually known by the code designation “VT” or “T-98,” and by the code name “pozit.” It contained a transmitter that broadcast a signal in flight. When the beam bounced off a solid object, a receiver in the fuse detected the reflected signal and tripped a firing circuit that detonated the shell. A five-inch pozit shell, fired by USS Helena in the South Pacific, had for the first time brought down a Japanese plane in January 1943. But for eighteen months, use of the fuse was permitted only over open water or friendly territory, for fear that if the enemy retrieved a dud, their engineers could copy the design.
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 at army bases in the U.S. showed that regardless of terrain, weather, or darkness, even targets below ground level, such as trenches, 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.”
Workers prepare armor-piercing shells at a U.S. factory that was converted from aluminum production.
With approval from the Joint Chiefs of Staff in late fall, SHAEF 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 debut: when AUTUMN MIST began, Eisenhower moved up the release of the weapon by a week. A gunner in the 99th Infantry Division described “piles of shells with many men using wrenches and hammers to bang off the one [fuse] and install the other.” Within days of the first use by field artillerymen, reports described “the slaughter of enemy concentrations east of Bastogne and interdictions of the principal enemy supply routes west of St.-Vith.” The 12th Army Group cheerfully reported that the pozit fuse “is a terror weapon.” SHAEF concluded that “the enemy has been severely upset.”