BERNARD SMITH of Barnstaple in Devon, originally a Willenhall lad, has sent the following detailed explanation of the ingenious system used by the Luftwaffe to guide their bombers to British targets during the Second World War — as referred to in one of the letters on the West Bromwich bombings we published in December. Bernard writes: "Following on from John Aston's fascinating update (December 27th, 2012) of the West Midlands' ordeal from enemy bombing, I was interested in his reference to the XGerat guidance system for the Germans' aircraft.
"In essence it was comprised of four beams radiating from Boulogne and Cherbourg— see diagram.
Each beam was named after a German river; beams Rhein, Oder and Elbe were transmitted from Boulogne, and beam Weser from Cherbourg.
Accurate "The raiders would follow roughly along the path of Weser (transmitted from Cherbourg, directly in line with Coventry).
When the plane crossed the Rhein beam it would more accurately follow the course, then after another 30 kilometres on to the next beam Oder, which then initiated the bomb release mechanism. Once beam Elbe was reached, a timer was automatically initiated, giving a 50 second period to bomb release.
"The beams were a highly directional VHF 'carrier wave', modulated with an audio signal to alert the pilot/navigator that he was crossing one of the beams.
"Prior to X-Gerat they used a system called Knickebein (Crooked Leg). This comprised a beam from the French coast aimed at the target.
The pilot would be guided along the course aurally. If he strayed from the course, he would hear dots or dashes, indicating to which side of the route he had deviated.
"Shortly before reaching the target a second beam would intersect the primary beam (on which he was travelling) giving a different sound which gave him a precise distance to target.
"Following on from the X-Gerat, the Y-Gerat was developed. This guidance system utilised a single beam known as Wotan (a one-eyed god). This single narrow beam allowed pulses to be transmitted which were immediately bounced back to the ground station, informing the Germans exactly how far the raider was from the target."