The Battle of Britain Five Months That Changed History, May—October 1940 by James Holland (z-lib.org).epub

ordination. ‘Our communications,’ noted Ulrich, ‘would continue to be
fatally flawed.’
Instead, the Luftwaffe had concentrated on looking to use radar and radio
technology to develop in-flight aids for navigation and bomb-aiming. In
many ways, this was logical. After all, since the Luftwaffe had so far
always been on the offensive there was less need for an early-warning
system such as Dowding had established. They had thus, since the midthirties,
been developing a series of three electronic bombing and
navigational aids, and two of these were available for use in Göring’s
bombers.
Since joining Air Intelligence, Dr ‘RV’ Jones’s brief had been to try and
obtain early warning of any new weapons or methods used by the enemy.
Although he had been spending time researching German self-sealing fuel
tanks and magnetic mines, it was towards aids to navigation that RV had
been devoting much thought. In early March, he got an interesting lead.
Captured German aircrew were all interrogated, but also placed together in
bugged cells. Air Intelligence’s chief interrogator, Squadron Leader Denys
Felkin, passed on to RV details of a conversation in which one prisoner was
telling another about a device called X-Gerät, or ‘X-Apparatus’. ‘The
beginning of a thriller,’ noted RV, ‘could hardly have had a more intriguing
title.’ This was potentially more exciting than the very best thriller,
however. From what the prisoner was saying it certainly seemed that X-
Gerät was a bombing apparatus using pulse radio technology, and the more
RV thought about it, the more it seemed likely that it was a system of
intersecting radio beams from German transmitters, and that where the
intersection occurred was the target – hence the ‘X’.
For the time being, however, RV got no further, but then, later in March,
he was passed a scrap of paper, found on a downed Heinkel 111, on which
was written: ‘Radio Beacons working on Beacon Plan A. Additionally from
0600 hours Beacon Dühnen. Light Beacon after dark. Radio Beacon
Knickebein from 0600 hours on 315 degrees.’ It was the phrase
‘Knickebein on 315 degrees’ that really interested RV. Further interrogation
by Felkin revealed that Knickebein was indeed a bomb-aiming aid a bit like
X-Gerät, but, other than that, for the time being RV could make no further
headway at all.