GERMAN BOMBERS MISLED BY BRITISH HOMING DEVICE

Press, Volume CXI, Issue 32661, 17 July 1971, Page 11

GERMAN BOMBERS MISLED BY BRITISH HOMING DEVICE

(By DAVID LEWIS)

Thirty years ago in the early hours of May 9, a squadron of Heinkel-111 bombers of the crack German Kampf Gruppe 100 lifted into the pitch-black sky from airfields in occupied Europe.

Their target was the Rolls-Royce factory at Derby where more than half of Britain’s aircraft engines were being produced. It was to have been the first of two disastrous knock-out blows which, if successful, would almost certainly have brought Britain to her knees.

On paper, the Germans must succeed. They were using top-secret radio direction device capable of guiding the bombers automatically to their target. The device, boasted Goering, would bring about the total destruction of the British war effort within weeks.

But what happened in the next few hours proved to be a key turning point of the Second World War— a momentous victory • that was to give Britain invaluable breathing space and so pave the way to the eventual defeat of the Nazi menace. Automatic signals Ironically, the radio navigation device the Germans were using on that raid on Derby had first been thought of by British scientists’, indeed, some airfields in Britain had been equipped with it. But in the early days of the war, it was crude and severeljklimited in range. What it did was to guide aircraft through bad weather on their final approach to the

airfield by sending out automatic signals from two ground transmitters. One transmiter beamed a series of dashes, the other a series of dots. The pilots would then position their aircraft until the dots and dashes coming through their earphones become one continuous signal. And as soon as the two signals merged the pilots knew they were dead on course for home. If the signal became a series of dashes again, the plane was too far to the left. A sequence of dots, on the other hand, indicated the plane was too far to the right. It was this simple concept which the German technicians had worked on, and they had succeeded in ironing out the snags. And using a long-range, narrow transmission beam, they produced a navigational aid so subtle that it could guide pilots over a distance of hundreds of miles to drop their bombs within 100 yards of the tarThe British had allowed themselves to be talked out of the device’s potential as a

long-range, navigational aid on the grounds that it was a technical impossibility. Then, in the early spring of 1940, a German bomber was brought down in one piece over Southern England. And among documents recovered by the Intelligence officers was one referring to a mysterious “knickebein beacon.” When this was passed to the Air Ministry’s experts for evaluation, most of them concluded it was a blindlanding approach-system. Detailed searches But one man did not agree. He was Dr R. V. Jones, who had carried out early experiments into methods of detecting enemy aircraft. Jones believed it was possible to extend the range .of radio direction ' equipment and, more important, to produce a narrow beam, along which to navigate.

Throughout the spring and summer of 1940, evidence began to accumulate which suggested to Jones that his hunch was right. Others came round to his way of thinking, particularly when captured documents and information gleaned from the interrogation of German aircrew all pointed to an advanced form of radio navigation. But detailed searches of the cockpit of shot-down bombers failed to reveal any of the new gadgets. It was then that Jones had an idea. Picking up the telephone he called a number of experts who had been searching the enemy aircraft, and asked if they had noticed any thing odd about the blind landing equipment. Clear signal In every case the answer was: “Not really—except we can’t understand why it is so sensitive.”

It was the reply Jones had hoped for. The Germans had concealed their new equipment by building it into standard navigation gear. Now that the receivers had been located in the bombers, the next task was to locate the beams. And on the personal orders of Churchill, three Anson aircraft equipped with short-wave receivers took off to search the sky for them.

At 5000 ft above the Midlands, one of the pilots— Flight Lieutenant H. E. Button —picked up a clear signal on 31.5 megacycles. It was a series of dots trans-

mitted on a beam only a third of a degree wide. Then, flying for 10 minutes to the north, he located a second beam transmitting a series of dashes. By flying between the two, a German bomber pilot would have been directed to the blacked-out armaments. factories of the Midlands.

More alarming discoveries followed. The scientists found the beams could also take the German pilots directly over the Derby Rolls Royce factory—an area defended by only 22 guns. Then, by simply adjusting their transmitters, the Nazi technicians could send their pilots straight over Bristol where the other half of Britain’s aircraft engine production was located. And the Bristol works were defended by only eight anti-aircraft guns. The answer Jamming was a crude answer, though it worked for a time. Using heating equipment commandeered from local hospitals, the scientists were able to surround important areas with a blanket of radio “noise” that blotted out the direction beams.

But jamming was swiftly overcome by the German technicians. The only answer. Dr Jones and his colleagues realised, was to devise a method of changing the beam’s direction without letting the Germans know. By May 1941, despite the increasing sophistication- of German equipment, they succeeded. Two British transmitters filled up the spaces between the German dots and dashes to produce a continuous, meaningless signal. They then transmitted their own “dot-dash” beams in a totally different direction. The system swung into operation on May 9, 1941, and, instead of, knocking out the Rolls-Royce complex, the bombs from the Heinkels fell many miles from the intended target. On May 30, another beam-bending operation by the British took Nazi fliers so far off course that they bombed neutral Dublin. From then on, though the German technicians struggled to devise new beaming techniques, the real threat was past. Thanks to the work of Dr Jones and his colleagues, Goering’s vaunted secret weapon proved to be as ephemeral Hitler’s 1000-year Reich.—Provincial Press Features. • ; 's ■