RADAR Manufacture WWII

Chris Poole


As readers will see from other articles on this website, EKCO re-located to Malmesbury as part of a government master plan to disperse strategic manufacturing to secret Shadow Factories, which would render them safe from German attack.

In order to give some idea of why EKCO Malmesbury was so important to the war effort, it has been said that WW2 was as much a ‘Radar War’ as a physical war.

It’s also true to say, that throughout history, wars are won by the side with the best technology and in WW2 this was very much a close run thing since there were many occasions when the Germans introduced new technologies and equipment, which the allies had to counter.

The redeeming factor was that in Radar thanks to the work done by Robert Watson Watt and his pioneering team at Bawdsey and later at the Telecommunication Research Establishment (TRE) at Worth Matravers we largely kept one step ahead and this was due in part to the equipment made by EKCO.


The development of the CH (chain home) early warning radar system is well known and documented. What is not so well known is that at a very early stage it was recognised that this system was inaccurate insofar as being able to direct fighters onto incoming attacks since CH could only direct fighters to the general vicinity of the intruders. (Which was not a problem during the Battle of Britain since the Germans by and large sent over large waves of aircraft, which were visible from a long way off) and if the intruders came by night, the night fighters would not be able to see them!

Recognising this Henry Tizzard asked a scientist called Eddie (‘Taffy’) Bowen at Orfordness to investigate the feasibility of putting a radar system (AI) onboard the aircraft, which would allow the crew to home onto the enemy.

Eddie (‘Taffy’) Bowen agreed to investigate and after much discussion with colleagues and RAF fitters from nearby Martlesham Heath he deduced that it was possible. His objective was an airborne radar system that would weigh no more than 100 kilograms (220 pounds), consume no more than 500 watts of electrical power, and use antennas no longer than a metre (3 feet 3 inches).

After submitting his proposal to Henry Tizzard, he was asked to proceed with bringing the idea to reality as soon as possible.

Taffy’ Bowen in the rear seat of Fairey Battle K9208, which was the principal aircraft used for test flights of 200 M/c/s airborne radar (the standard frequency used for AI Mark I to IV inclusive).

Photo courtesy of the Institute of Physics

Given that this was 1937 and the technology of the time meant that the CH station’s electronics filled up rooms to say nothing of the massive power demands whereas space, weight and electrical power were at a premium on aircraft this was a major challenge (aircraft at that time only generated and used not more than 500 watts?).

Initial experiments were conducted in the early summer of 1937 with a modified Heyford (bi-plane) bomber. The bomber didn’t carry a transmitter, instead it only had a receiver, which picked up the ground transmitter pulses and the echoes and try to make sense of them. Bowen was enthusiastic about the scheme, but it was tricky to get to work. The idea was basically sensible but beyond the technology of the time.

Having learnt from the experiment, Bowen and his team went back to the drawing board and refined the equipment with the next set of tests using an AVRO Anson in the late summer of 1937, which is ironical when you consider that 20+ years later EKCO themselves were using an Anson as their flying test bed.

The testing did not detect any aircraft however the team were asked to take part in a Naval exercise in September 1937 in weather so poor that normal reconnaissance aircraft were grounded. This flight showed up the Naval ships in the predicted area which they were able to relay to the commander of the exercise, which confirmed the possibility and practicality of Air to Surface Vessel (ASV) radar.

Editors Note: To read the full and fascinating history of airborne radar development, the editor recommends the book ‘Radar Days’ written by E G Bowen and published by the institute of Physics ISBN 0-7503-0586-X

The wartime radar sets

In the meantime development work was still continuing on AI radar although the first AI system (Mark I) was considered a bit of a disaster since it was unreliable and primitive even when it worked. The next set the AI Mark II wasn’t that much better, however since everything about AI was completely new, it was a bit like learning on the job both for the night fighter aircrew, the ground crew (who had to maintain the system) and the scientists themselves – who were also learning the needs of the aircrew.

The original sets were fitted into Bristol Blenheim’s, which events were to show were too slow and too poorly armed to be very effective. Following their disastrous performance in the Battle of Britain, the radar was also tried out in the Bolton Paul Defiant although this was no more successful.

The next model (AI Mark III) was an improvement and did give Night fighter crews a sporting chance of an interception however the radar had a maximum range of about 2,750 metres (9,000 feet) under optimum conditions, and a minimum range of about 250 metres (800 feet).

The shortcoming of the system being that to obtain a successful interception, ground controllers still had to guide the aircraft onto the target very accurately if the radar was to have any chance of detecting the intruder and by and large it still took a lot of skill and judgement by the pilot to obtain a kill.

This radar was fitted to the Blenheim (and later the Beaufighter) consisted of a transmitter aerial in the nose of the aircraft and a pair of receiving aerials well outboard on each wing. This allowed the radar operator to judge if the target was to the left or right of the aircraft and above or below, thereby allowing the pilot to turn into the target.

Recognising that there was still considerable scope for improvement, the help and assistance of Alan Dower Blumlein who was considered Britain’s most prominent electrical engineer was enlisted along with EMI who manufactured the high definition CRT display using their technology developed from TV screens.

Bringing in a top professional was a great help to the often ingenious but sometimes-amateurish scientists, and Blumlein was able to develop a fast pulse-switching scheme that cut the minimum range of AI to 130 metres (426 feet) thus giving the night fighter crew a better chance to obtain visual contact.

The result was AI Mark IV, which was a major step forward from its predecessors and the first set made in volume by EKCO Malmesbury. In all it is believed that some 3000 Mark III and IV units were manufactured between 1940 and 1942.

This radar was initially installed in Blenheims although the majority were fitted to the Beaufighter, which came into service as the Blenheim replacement; this version was also fitted to early Mosquitoes and initially was the only unit to be allowed to fly over occupied Europe due to concerns about ‘magnetron’ technology falling into enemy hands.

The shortcoming of the Mark IV was that it operated on fairly long wavelengths (195 MHz) and it was underpowered i.e. it could not generate a strong enough radar beam for long range target acquisition.

Due to aerial design, strong echoes were received from the ground directly under the aircraft, which of course meant that tracking signals when flying low was particularly difficult, due to the target echo being swamped by ground return signals, which effectively limited the range. The maximum range was roughly the same as the height of the aircraft i.e. if the aircraft was at 6000 feet; the radar range was also 6000 feet.

On the plus side, the sets had become much more reliable, their operators became far more competent due to better training and invariably the good pilots recognised that they needed to team up with radar operators, which in turn meant that night fighter crews started to accumulate significant numbers of successful interceptions and kills.

Two night fighter aces to emerge as a result of flying Beaufighters with AI Mark IV were Wing Commander John Cunningham and Wing Commander John Braham.

Description of the ASV Mark II

The ASV Mark II worked on very similar principles to the AI Mark IV however only two aerials were required (port and Starboard) since there was no need to measure the height of the target – for obvious reasons. Again the mark II was a major step forward from its predecessor.

Another variation of the radar used a large aerial array mounted on top of the fuselage. This was used broadside on for sweeping shipping lanes. The system could also be used as a beacon receiver at ranges up to 90 miles.

EKCO Malmesbury also made these sets in volume. As with the AI Mark IV, it is believed that some 3500 ASV Mark II units were manufactured between 1940 and 1942.

The sets were installed in many Coastal Command aircraft including the Vickers Wellington Mark XI and later in the Consolidated Liberator when patrols began to extend out into the Bay of Biscay and the Atlantic.

The Fleet Air Arm also fitted ASV Mark II as standard to their Fairy Barracuda Mark II aircraft.

These radars were of assistance in countering the U-Boat menace and did give the Germans cause for concern as the number of U-Boat loses mounted. It continued to give the Allies an edge until a Wellington unfortunately crashed over occupied territory and from the wreckage, the German scientists were able to determine the operating frequencies, which then enabled them to build a radar-warning receiver for the U-Boats called ‘Metox’.

The next Generation (Cavity Magnetron) Radars

While the AI Mark’s III & IV worked well, the scientists at TRE had already recognised that there were many limitations of a radar system operating on a 1.5 metre frequency and that radar would work better at shorter wavelengths, which would provide a finer resolution, a tighter beam, and would not be swamped by ground return signals.

To investigate and pursue the use of radar, which would operate in the 10 Centimetre band, a team was set up at TRE Worth Matravers. Co-incidentally, the Admiralty had also set up a special committee to investigate microwave radar that would operate on a ten-centimetre wavelength and they assigned the Clarendon Laboratory at Oxford to work on a microwave receiver, while a team from the physics department at the University of Birmingham was to work on a microwave transmitter.

John Randall and Henry Boot at the University of Birmingham made the real breakthrough. They were not at the heart of the transmitter development, all they were simply trying to develop was microwave detector circuits but to test their designs, they had to generate microwaves for their circuits to detect. Randall and Boot didn’t know much about generating microwaves, so they set about learning how even though they were working on a shoestring budget.

The result was that they developed the Cavity Magnetron, which they powered up for the first time on the 21st February 1940.

Within a few days their magnetron was producing a power output in the order of 500 watts, which was enough to light up fluorescent tubes from some distance away. It is reported that they found this incredible and caused them to check and re-check their figures and the experimental set-up, but nothing was wrong.

The result was that the magnetron – at a stroke – gave the scientists the leap forward in microwave technology, which they were seeking and over the following months intense development work took place to refine the magnetron and transmitter into something resembling an operational system, with a maximum output power of 15 kilowatts, which was something like three orders of magnitude greater than the output power available with any other device.

The TRE received its first cavity magnetron on 19th July 1940. A microwave radar system operating at 9.1 centimetres was quickly assembled and tracked an aircraft on 12 August 1940.

Rather than use the static aerial system from the Mark IV, a dish based scanning system was also developed.

AI Mark VII and VIII radars

Following the prototype work, the Mark VII and VIII radars were developed to a production stage and in early 1942 an initial order for 1000 sets was placed on EKCO, these units began to be delivered towards the end on 1942 and its first successful intercept and shoot down of a German aircraft is recorded in January 1943. In all EKCO manufactured circa 5000 Mark VIII sets and associated test equipment during the course of the war.

A new type of indicator display (spiral display) was developed as well as a new type of display screen, which meant that the all the information was shown to the radar operator on one screen.

Both the dish and screen were remarkable designs, the scanner dish was 28 inches in diameter and rotated at 200 RPM (although it was capable of 960 RPM) whilst tilting up/down and left/right, this creating a beam that was spiral on pattern. The screen displayed information in a circular format, which once used to, was easy to interpret.

This radar was fitted to both Beaufighter and Mosquitoes, with strict instructions NOT to fly over enemy territory in the early days although this was relaxed when night-fighters were sent out with the bomber stream from late 1943 onwards. It is easy to recognise either aircraft using Mark VII or VIII radar since they both had what became known (for obvious reasons) a thimble nose.

AI Mark VIII continued to be the mainstay of night-fighters throughout 1943 and 1944 only being superseded by the American developed SCR720 set, which used similar technology to the Mark VIII, but had twin scopes and was considered less susceptible to enemy jamming. This was adopted in the UK as AI Mark X.

Radar operators had to learn how to interpret the AI Mark VIII screens since it presented information in a completely manner from the Mark IV system, nevertheless, once they got used to it, it was quickly recognised and accepted as being much simpler to understand than the Mark IV.

In the example shown, the inner ring represents zero range. The outer ring represents the aircraft altitude (4000 ft for example) and the horizontal band is due to ground return echoes although it conveniently also acted as an artificial horizon.

The arc off to the left is a target echo, which is about 20 degree’s off the aircraft heading and at a range of about 2 miles.

As the night-fighter turned towards the echo, the arc of the echo would increase until it became a full circle when the enemy aircraft was dead ahead. As the range decreased the circle would get smaller and once it intercepted the small inner ring, the enemy aircraft should certainly be within visual range and possibly also gunnery range.

Some of the above photos of the AI Mark VIII are courtesy of the Dutch Signals Collection, which is a non profit organisation dedicated to collecting and preserving wartime radio and radar equipment. Their website can be found at www.qsl.net/pe1ngz/signalscollection.html

I am also indebted to Charles Exton for allowing use of photos from his private collection.

EKCO and bomber fleet equipment

During trials of the AI Mark VII, it was noticed that identifiable ground returns showed up. This lead TRE to a revival of an earlier idea for the use of radar for navigation and lead Dr Lovell and his team from TRE to investigate further in association with Alan Dower Blumlein and his team at EMI with the end result that EMI were largely instrumental in developing H2S to a production standard.

There is no record that EKCO were directly involved in H2S manufacture, however is fair to say that there was a lot of interchange of information via TRE.

What EKCO did make, were the standard radio transmitter/ receiver units for the bomber fleet, known as T/R 1154/1155.

These were made in another EKCO shadow factory located in Ashton Clinton Nr Aylesbury.

Oslo Fjord – Norway 28th December 1944

On the 28th December 1944, we were one of four crews briefed to carry out a raid on Horton Harbour in the Oslo Fjord where our mission was to find and sink two German light cruisers – the Koln and the Emdon, which were known to be sheltering in the Oslo Fjord at anchorage just offshore from the small town of Horten.

We were able to use our normal aircraft OL ‘E – Easy’ (Note: OL is the code letters for No.83 Squadron, E being the letter to indicate an individual aircraft within the Squadron.) and the bomb load was made up of two Red/Yellow and two Red/Green Wangannui marker flares, eight Marine Floats, two Flame Floats and ten 1000Lb HE Medium Case bombs.

We would be the Pathfinder Force and would be joined by a Mosquito who would assume the role of Master Bomber and the main force of 63 Lancaster’s would follow us in.

Weather conditions forecast for the target area indicated complete cloud cover, and the carrying of Wangannui marker flares meant that blind bombing techniques would be used.

It was therefore vital that the H2S equipment was in top-notch condition since only aircraft equipped with this would be able to ‘see’ the target area on their screens.

Wangannui marker flares were designed as airborne flares (also known as Skymarkers), which were dropped by the Pathfinder force when there was complete cloud cover of the target. They were dropped on the calculated point of weapon release by the main force who were flying close behind the pathfinder force at the same height and speed and the main force would aim to bomb release onto the markers.

In order to be successful using this technique timing and accuracy was all important both for the Pathfinders and the main force since both had to pass through the target area in the minimum of time

In the event our aircraft (OL-E) was able to report that cloud cover was thin and that visual identification was possible.

The target ships were not in their briefed position and it was necessary to make three separate runs over the target area before we were able to successfully target the Koln.

Enemy defence was heavy due to a previous attack 3 weeks earlier, however no aircraft were lost although OL-E was badly holed by predicted flak but nevertheless pressed home her attacks and for this the Captain was awarded the DFC.

The photo below was taken during the raid and clearly shows that the H2S radar was capable of providing a very good picture of the terrain and was able to allow the radar operator to discriminate large targets such as the Koln.