Plessey Exchange Works
The factory was built
in the 1950s in order to hide classified design and manufacturing
of the UK Air Defence System away from prying eyes. It was an
extension of the ATE (Automatic Telephone & Electric Company)
based nearby in Edge Lane, Liverpool. Alas, with the end of the
Cold War the British defence industry collapsed and the building
was turned into luxury flats. The site was alongside Cheapside
at the front and Cunliffe Street at the rear. Adjacent to the
site across Cheapside Alley was a small factory that made candles.
Looking at the picture below, the far end of the factory housing
laboratories, some manufacturing, and the factory canteen, before
being bought by ATE, made margerine and (so I'm told) during
WW2 bombing a direct hit resulted in a stream of molten margerine
running down Cheapside.
Looking a bit gloomy,
a view along the old Plessey building to the Liverpool Municipal
Building in Dale Street.
What went on in the building
where I worked for 20 years? I've managed to find some rare pictures
of the equipment (thanks to Terry Pate who was my boss for quite
a few years before moving to the radar division on the Isle of
Wight where he was the Managing Director).
The first picture is the XL4
computer of which a couple of dozen were manufactured. This was
a 64 bit machine that worked asynchronously rather than being
governed by a master clock. As you can see it has five cabinets
and each was stove enamelled with chrome-plated fittings.
The XL4 was developed from the
XL2 (awaiting a picture). An early XL2 handled the wages for
Exchange Works staff and had about twice the number of cabinets
of the XL4.
I understand the XL4 was
designed by Ron Threadgold and Dave Hartley (who together also
designed the XL2); and Terry Pate (who supplied these pictures)
worked on the XL4 processor. Linesman was known as PLCS to muddy
Each cabinet housed a number
of plug-in units carrying about 25 printed circuit boards whose
connections were wired to a frame by gun-wrapping. The circuit
boards carried standard logic functions constructed from germanium
transistors and diodes with their interconnections made in the
wiring of the unit frame. This method made the design quite complicated
but allowed for standardised logic functions equivalent to todays
integrated circuits ie. each circuit board, say for example six
inverters was equivalent to a modern logic chip such as a 7404.
Like a modern PC the XL4 needed memory, and this was 32K x 64
bit x 2uSec, and occupied a couple of 7 foot cabinets.(nowadays,
double this amount of RAM would occupy just a few square millimetres
within a microprocessor chip)
Next a rare view inside RAF
West Drayton computer room... Note the "wiring" carrying
power to the computers.. enormous copper busbars in the ceiling
driven by a number of hundred amp power units backed up by lead
acid batteries. and the trunking carrying cooling air to keep
the fragile germanium transistors safe. There were several power
supply voltages and it was vital to turn these on/off in the
correct order to avoid thermal runaway in the germanium transistor
junctions. The computers operated in real time and were responsible
for tracking and predicting the course of enemy aircraft. Radar
sites around the UK coast picked up echoes from all aircraft
in the vicinity of the UK and transmitted data to West Draton
where it was processed by the Linesman computers with results
passed to display consoles.
If I recall correctly, the room
above this were something like 70 radar display consoles.
If you'd like to see an
outstation, RAF Neatishead, just as it was when Linesman was
scrapped visit the Radar Museum close to Horning in Norfolk.
The next major development was
the XL6 computer (designed by Terry Pate), a 24 bit machine.
Left the computer and right its memory. This was supplied as
a message swich for ICI.
Then the XL7.
Next was the development
of the XL9 computer (awaiting pictures)
This was a commercial venture
designed by Terry Pate and Dave Paculabo, and was used in a number
of projects including an air defence system for Burma, a telephone
exchange in London, a message switching system based at GCHQ
Oakley, a wide area traffic control systems in Liverpool and
West London (awaiting pictures).
Following up from the
XL9, a venture into a more advanced machine was the XL12 which
unfortunately fizzled out... see below... but Exchange Works
did design and develop a new computer for the management of telephone
exchanges. This was known as "Sprat" and three computers
were manufactured and installed at the Plessey site of Taplow
near Heathrow. These computers were again based on ideas from
XL9 and XL12 and were designed to be fault tolerant. A loss of
one or two machines from three would result in the remaining
system of two or even a single machine picking up the workload
without any hesitation. To demonstrate this to the customer it
was arranged that test software was written and an audio amplifier
connected to part of the computer to produce tones. Using the
test software a musical tune was produced, that was "English
Country Garden". During playback one computer was turned
off and then a second with no hesitation in the tune. Then the
computers were re-introduced and again no hesitation in the tune.
Meanwhile, sharing the
top floor of Exchange Works with the Drawing Office, and even
more secret than Linesman, took place the design and development
of crypto equipments, a few of which are pictured here. Left
is the BID610.
Besides manufacturing complete
equipments, Exchange Works developed the small unit forming the
most important part of most UK cryptographic equipments, the
noise generator; based on a semiconductor junction or zener diode
which was able to provide completely random binary code used
to produce the key for encrypting messages..
Below, newer machines.. first
Then, below the more compact
When Margaret Thatcher
decided to sort out troubles in Northern Ireland, Exchange Works
won contracts for the design and development of specialised military
equipment. These included P6 (a mine detector), P7 (a device
for detecting command wires for things like A mines hidden in
trees), IA2 (a device for recording sounds from terrorst activities),
IA5 (a sniper detector), 3PS (an intruder detection system) and
others (awaiting pictures).
At roughly the same time,
Exchange Works entered into the satellite business. Monitoring
and control equipments were supplied to support the ground station
handling the GEOS and METEOSAT satellites and others, managed
by ESOC in Bretigny and Darmstadt. This area of expertise ended
once the design, development and manufacture of equipment for
RAF Oakhanger (the anchor station for Skynet) had been completed
and installed (awaiting pictures).
Because of expertise from
previous air defence systems, Exchange Works provided the communications
cabins for a number of 3D-radar based air defence systems including
those for South Africa, Egypt, Ecuador and Qatar, plus inadvertently
helping out when the Falkland Islands were invaded by diverting
one of the systems for Qatar. Below.. a comms cabin for Project
Rodent. Because of their large physical size these cabins were
manufactured on the second floor of the building because lower
down the building support pillars were too close together. A
doorway needed to be cut into the side of the building through
which a crane could deliver empty containers and collect equipped
cabins for transit, usually to Bournemouth Airport.
Is that everything? Not
quite.. Exchange Works also supported otherPlessey businesses
by designing and manufacturing all sorts of interesting things.
These included parts of radar jamming equipments (for Syria would
you believe...), message heading generators for NATO (because
we had experience with ACP127 for GCHQ), the Store and Forward
Message Switch for Ptarmigan, studies for Ptarmigan and Wavell
for the British Army and specialised equipment for Eurocontrol.
This last equipment comprised a pair of 128-input multiplexers
using lots of microprocessors developed before those from Intel.
The design of these was based on the type of work that had gone
into the XL12 computer which was being built for commercial systems
but had been cancelled when Plessey and others formed ICL. The
pair of multiplexers were installed at Karldap and used for combining
peripheral equipments into Telefunken computers for the control
of middle airspace over Europe (picture?).
Anyone with more information
or corrections please contact me.