JED - June 2016 - 43

SIGINT History

"YOU LIKE TOMATO AND
I LIKE TOMAHTO..."
By Martin Streetly

these counts, it was decided that the
only suitable aircraft was the Fortress."
A more detailed picture of the
planned escort jammer can be gleaned
from the minutes of a meeting that was
held at RAF Bomber Command's HQ on
January 12, 1944. Here, we are told that
the Command had requested the supply
of an initial batch of 14 B-17s from the
American Eighth Air Force, with each
aircraft to be fitted with the H2S bombing/navigation radar; the Gee or LORAN
hyperbolic radio navigation aid; an air
position indicator computer (with an air
mileage unit); a Monica IIIA tail-warning
radar; medium-, high- and very-highfrequency communications gear; the
Jostle IV communications jammer and
four Airborne Grocer AI radar jammers.
Elsewhere, the minute noted that
each B-17 was to be fitted with rear,
mid-upper and ventral (subsequently
deleted) gun turrets and was to be flown
by a crew comprising a pilot, a navigator,
a flight engineer, a wireless operator, a
"special operator" (SO), an "air-bomber"
(bombardier - to act as a second navigator and as an air gunner) and two
gunners. In terms of performance, a
fully-equipped aircraft (with an overall
weight of 27,442 kg and all the specified
avionics, jammers and defensive turrets
installed) was expected to have a range
of 1,851 km when flying at a speed of
378 km/h and an operational altitude of
9,144 m (30,000 ft).
The key to the Air Ministry's stress
on altitude was the presence of Airborne
Grocer in the proposed B-17 fit. As outlined in the quoted report, Airborne
Grocer was aimed at the German FuG

202/212 AI radars and was designed to
"barrage" to within ± 60 MHz of their
490 MHz center frequencies. To provide
the desired coverage, it was proposed to
allocate six Airborne Grocer aircraft per
"stream," with the individual aircraft
flying approximately 1,524 m (5,000 ft)
higher than the stream, so that its jamming output formed a "slightly downward" pointing 60° cone whose apex was
on the tail of the transmitting aircraft.
So arranged, that part of the stream behind and below the B-17 would be protected, with the six aircraft package
being calculated to be able to "envelope
the whole length of the [stream] in effective AI jamming."
For its part, Jostle IV is characterized
as covering the 3- to 54-MHz band in six
sub-bands; as weighing more than 272
kg; as being pressurized, and as having
a 2.5 kW output. Again, the device was
deemed to be a "prime need" in order
that the enemy might be more effectively denied use of high-power, high frequency transmitters to convey orders to
his night-fighters. "Prime need" or no,
the introduction of both Airborne Grocer
and Jostle IV did not go to plan and in
the words of the report, "it was a long
time before either of these projects ...
came to fruition." Of the two, Airborne
Grocer finally became available in June
1944 at which time, it was realized that
the prevailing night-time light levels
over Europe were such as to allow the
enemy to complete the final stages of
an interception without having to resort
to radar. Again, active jamming in such
conditions was held to be likely to act as
a "long-distance AI beacon," and it was

The Journal of Electronic Defense | June 2016

mong the many airborne EW
techniques pioneered by the
Royal Air Force (RAF) during the Second World War,
was the use of specialized
escort jammers, which
were used to support its bomber offensive
against targets in Germany and occupied Europe. According to RAF Bomber
Command's War in the Ether after-action
report on its "radio countermeasures"
(RCM) campaign (published in October
1945), the origins of the capability can
be traced back to a meeting that was held
on July 15, 1943, at which, the feasibility of protecting bomber "streams" with
a "few escorting aircraft fitted with specially-designed, high-power equipment"
was discussed. After due consideration,
it was decided that such a scheme was
possible, and that the aircraft-of-choice
should be the American B-17. The aircraft should be equipped to jam the
enemy's ground-to-air communications
and his airborne interception (AI), gunlaying/ground-controlled interception
(GCI) and early-warning radars "in that
order of priority."
Selection of the B-17, rather than a
British aircraft, was predicated on three
considerations, namely the perception
that the best way to counter the enemy homing in on airborne jammers was
"height," that there were "no operational [British] aircraft to spare," and that
the B-17 was understood to be able to
fly "as fast and as far" as British bombers at a "greater height." It also must to
be big enough to carry the necessary
equipment and generate enough power
to run the onboard electronics. "On

43



JED - June 2016

Table of Contents for the Digital Edition of JED - June 2016

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
Washington Report
World Report
Advances in COMINT/ DF Systems
Technology Survey: Communications and IED Jammers
SIGINT History
EW 101
Report from the 45th Annual Collaborative EW Symposium
AOC News
2016 AOC International Election Guide
Index of Advertisers
JED Quick Look
JED - June 2016 - cover1
JED - June 2016 - cover2
JED - June 2016 - 3
JED - June 2016 - 4
JED - June 2016 - 5
JED - June 2016 - The View From Here
JED - June 2016 - 7
JED - June 2016 - Conferences Calendar
JED - June 2016 - 9
JED - June 2016 - Courses Calendar
JED - June 2016 - 11
JED - June 2016 - From the President
JED - June 2016 - 13
JED - June 2016 - 14
JED - June 2016 - The Monitor
JED - June 2016 - 16
JED - June 2016 - 17
JED - June 2016 - 18
JED - June 2016 - 19
JED - June 2016 - 20
JED - June 2016 - 21
JED - June 2016 - Washington Report
JED - June 2016 - 23
JED - June 2016 - World Report
JED - June 2016 - 25
JED - June 2016 - Advances in COMINT/ DF Systems
JED - June 2016 - 27
JED - June 2016 - 28
JED - June 2016 - 29
JED - June 2016 - 30
JED - June 2016 - 31
JED - June 2016 - 32
JED - June 2016 - Technology Survey: Communications and IED Jammers
JED - June 2016 - 34
JED - June 2016 - 35
JED - June 2016 - 36
JED - June 2016 - 37
JED - June 2016 - 38
JED - June 2016 - 39
JED - June 2016 - 40
JED - June 2016 - 41
JED - June 2016 - 42
JED - June 2016 - SIGINT History
JED - June 2016 - 44
JED - June 2016 - 45
JED - June 2016 - EW 101
JED - June 2016 - 47
JED - June 2016 - Report from the 45th Annual Collaborative EW Symposium
JED - June 2016 - 49
JED - June 2016 - AOC News
JED - June 2016 - 2016 AOC International Election Guide
JED - June 2016 - 52
JED - June 2016 - 53
JED - June 2016 - 54
JED - June 2016 - 55
JED - June 2016 - 56
JED - June 2016 - Index of Advertisers
JED - June 2016 - JED Quick Look
JED - June 2016 - cover3
JED - June 2016 - cover4
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