Development of radar for the Royal Navy1935-44

J.D.S. Rawlinson, C.B.E., B.Sc.(Eng.), C.Eng., F.I.E.E.

Indexing terms: History, Radar and rationavigation

Abstract: The original patent for radar was registered by the Admiralty in 1928. However, it was not until 1935that the Air Ministry took the initiative to develop radar. Following a meeting at the Air Ministry in March1935, the Experimental Department of HM Signal School was instructed by the Admiralty, to start work on thedevelopment of radar for the Royal Navy. The paper describes the early development of radar, and its initialtrials in ships, up until 1944, when the Services Electronic Research Laboratory was established.

1 Introduction

Much has been written about the development of radar;the pioneer work done by Sir Robert Watson-Watt and histeams at Bawdsey, Swanage and RRE Malvern has beenwidely publicised. As far as I am aware, little has beenwritten about the early work carried out by the Experi-mental Department of HM Signal School, Royal NavalBarracks, Portsmouth, and not many references have beenmade to the vital contribution which this developmentgave to the Royal Navy during those years. I thereforewelcome this opportunity to write this article for theJournal of Naval Science.

The famous experiments of Marconi which establishedthe possibility of transatlantic communications and whichwere carried out between the W/T stations at Poldhu,Cornwall and St. John's Newfoundland, took place in1901. The development of radar for the Royal Navy beganin 1935; there is therefore a comparable interval betweenMarconi's experiments and radar development as there isbetween 1935 and today. To those acquainted only withthe sophisticated equipment of the present, much of theearly apparatus must seem crude and elementary but Iwould observe that today's intricacies have only beenmade possible by parallel developments in metallurgy andceramics and in the production of delicate measuringdevices which certainly did not exist in 1901 and much ofwhich was not available in 1935.

2 The patent for radar

Although the development of radar for the Royal Navybegan in 1935 it could have begun much earlier. Patent6433/28 dated 1st March 1928, Patent and Designs Act1907 and 1919 was lodged with the Patent Office and wasas follows:

2.1 Provisional specification(a) Improvements in and relating to methods and means

for determining positions, directions or distances of objectsby wireless waves, applicable to navigation and for thelocation of dangerous objects or of enemy craft.

(b) We, James Sacheverell Constable Salmond, Captain,Royal Navy, and Leonard Stanley Bater Alder, M.Sc,both of HM Signal School, Royal Naval Barracks, Ports-mouth, Hampshire, both British subjects.

Paper 4089A (S7/E15), was first published in the Journal of Naval Science, 1975, 1,pp. 159-165 and reprinted in Naval Electrical Review, July 1975.

The author was superintendant, Scientific Personnel, Royal Naval Scientific Service

(c) This invention relates to methods and means for theemployment of the reflection, scattering, or reradiation ofwireless waves by objects as a means of detecting the pre-sence of such objects and of determining the positions,directions or distances of such objects. According to thisinvention apparatus which may be placed on land or in aship or in aircraft, may be employed to generate wirelesswaves and to observe or detect their reflection, scatteringor reradiation from a surrounding object or objects or anearby object such as shipping, icebergs, natural land fea-tures or the surface of land or sea below an aircraft, orfrom suitable reflectors constructed for the purpose inknown positions as, for example, at points dangerous toshipping, the entrances to harbours, or at aerodromes andlanding places for aircraft etc.

It would be difficult to define radar principles moreclearly, yet little notice was taken of this patent by theAdmiralty and it was not exploited. The initiative waseventually taken by the Air Ministry in 1935. If the Boardof Admiralty had acted differently in 1928, no doubt navalhistory would have been different from what it is. Onething is certain, Alder never received the credit which hisbrilliant patent should have earned for him.

A meeting was held on 11th March 1935 at the AirMinistry with Sir Henry Tizard presiding. Among thosepresent were the Directors of Scientific Research (DSR) atthe Admiralty and Air Ministry and G. Shearing, Superin-tending Scientist at the Signal School, Portsmouth. Themeeting explored the possibilities of detecting aircraft byships of the Royal Navy. At this meeting Shearing referredto reports of interference effects which had been observedby the Post Office when using frequencies of the order of60 MHz between stations at Dollis Hill and Colney Heath.This interference was only noticed when an aeroplane wasknown to be in the vicinity.

On 10th July 1935 DSR, Admiralty received a letterfrom DSR, Air Ministry as follows:

'You are aware that a radio method for detecting andlocating aircraft is being investigated by the Air Ministryand that a number of the staff of the Radio Department,NPL, who have experience with the special techniquesinvolved have been lent for the work now proceeding atOrfordness. This staff is under the direction of Mr.Watson-Watt.

'It would be greatly appreciated if facilities were afford-ed Mr. Watson-Watt to obtain any assistance he mayrequire from HM Signal School, Portsmouth.

This Orfordness investigation has been given thehighest priority possible and is of course of a strictly secretnature'.

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This letter was forwarded to Signal School on 12th July1935 by DSR, who asked for facilities to be given and whoadded that the work would appear to be highly promising,not only to the Air Force, but also to the Navy and thatthe work would have applications other than for the detec-tion of aircraft.

Watson-Watt had used the apparatus which he haddeveloped for his ionosphere and Heaviside layer researchand had discovered that echoes could be received from air-craft. The equipment developed for the ionospheric experi-ments used the pulse techniques from which radartechniques followed as a logical consequence. SignalSchool undertook to make silica valves for Watson-Watt,and Captain, Signal School, stated that every effort wouldbe made to explore the possiblities of developing similartechniques for the Navy and modestly asked for anincrease in staff of one scientific officer and one assistant.

3 Early radar development work

In August 1935, the Controller decided that the Experi-mental Department, HM Signal School should start assoon as possible to develop apparatus to detect and locateaircraft by radio methods. A representative from SignalSchool went to Orfordness for six weeks and then at ameeting held at the Admiralty the requirements given inTable 1 were laid down:

Table 1 : Requirements for radar laid down by the Admiralty

Aircraft:

Ships:

Warning of approachPrecise locationWarning of approachPrecise location

60 mile (96 km)10 mile (16 km)10 mile5 mile (8 km)

On 30th September 1935 a letter was received from theBoard of Admiralty giving approval for the work toproceed.

The years 1935-37 covered the early research, based onthe work at Orfordness and governed by the necessity tostrike out on new lines of development necessitated by themore arduous conditions which would be met at sea.

The work ashore, on which the Coastal Chain wasbased, had focused on frequencies around 25 MHz using afloodlighting system and requiring for each station anumber of 250 ft (76 m) masts. Such a system was quiteimpracticable for a ship.

The frequency selected was decided by the usual com-promise between conflicting factors. The higher the fre-quency chosen, the better chance of accommodating asatisfactory aerial system in a ship; at that time, however,existing transmitter and receiver techniques favoured thelower frequencies. The floodlighting system could notcover 360° and therefore a rotating aerial at the mastheadwas required which of course introduced mechanical andweight problems.

The silica valve was a Naval development for W/T pur-poses in the Royal Navy and had proved its worth as ahigh-power valve not needing complicated coolingsystems.

Various experiments had been carried out in 1936 and1937 on different frequencies and it was finally decided todevelop a set operating on 43 MHz, that being regarded asthe lowest frequency for which a useful aerial could be pro-duced which could be installed at the masthead. Work ontwo development models was begun, each to have tworotating aerials one for transmitting and the other forreceiving, the two rotating in synchronism. These were

produced by the summer of 1938, the first installed inAugust in HMS Sheffield and the second in HMS Rodneyin October.

Meanwhile, work was also in hand to develop radarequipment for locating surface vessels and for improvingrangefinding. There were three teams working under C.F.Horton; the long-range team working at Eastney, of whichI took charge in February 1939, the surface and gunneryranging team under J.F. Coales at Onslow Road, Ports-mouth and Southsea Castle, and the aerial and propaga-tion research at Nutbourne under A.W. Ross. We werenot, of course, working in isolation; there was close co-operation and exchange of ideas.

4 Results of early trials

On 17th May 1938 Their Lordships had sent a letter to theCommander-in-Chief Home Fleet informing him of thedevelopments of radar and the intention to have two setsinstalled in the Fleet. A paragraph of the letter is worthrecording.

'The detection of aircraft is evidently not only the tacti-cal application of wireless echo location of interest to theFleet. Priority is also being given to the development ofthe locating of surface vessels and to the achievement, inthe more distant future, of an accuracy of continuous closerange location of aircraft sufficient for AA control andsearchlight purposes. Further, there is a possibility that theapparatus fitted in ships for aircraft detection may alsoprovide short ranges of aircraft with an accuracy appre-ciably higher than that of existing rangefinders'.

The results from both HMS Sheffield and HMS Rodneywere good. In October 1938 Sheffield reported the detec-tion ranges on aircraft given in Table 2.

Table 2: Detection ranges on aircraft

30 mile (48 km) at 3000 ft (914 m)48 mile (77 km) at 7000 ft (2134 m)53 mile (85 km) at 10000 ft (3050 m)

Although these two sets were experimental models, verygood consistent results were achieved. The equipment inHMS Sheffield was not replaced until 1941. Nevertheless,to produce this type of radar in quantity it was necessaryfor some redesign. Because of my previous experience withthe development of equipment for both HM Ships andNaval W/T Shore Stations I was fortunate to be selectedto take charge of the long-range warning team. Our firstduty was to produce a radar set not later than 30th June1939, the set to have undertaken satisfactory trials onshore, ready for installation in one of HM Ships andcapable of being produced in quantity.

This was done: the set was installed in HMS Curlewand with the new thoriated filament silica valves gave apulse power of 70 kW. Thus, just before war was declaredon 3rd September 1939, a completely designed long-rangewarning set was ready although not then available inquantity; however, 40 were on order.

In October 1939 both Sheffield and Rodney reportedsuccessful detection of enemy aircraft and later in that yearCurlew at Scapa Flow consistently detected aircraft flyingat 10000 ft at ranges of over 60 miles.

Trials in Sheffield and later in Curlew confirmed the pre-dictions that detection of ships would be possible. Theseearly results, though inconsistent, were sufficiently encour-aging to justify further work on this problem.

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5 Type 281: the first experimental model

During 1939 the team under J.F. Coales concentrated onfrequencies of the order of 600 MHz. The aerial systemswere smaller and lighter, important factors for equipmentfor HM Ships. In conjunction with GEC Research Labor-atory, Wembley, a triode valve of adequate output and rel-iability was produced and used in a set designed foraccurate detection and ranging of surface targets.

In 1939 we had sufficient confidence to proceed with thedevelopment of a very high-powered long-range warningset which would also detect surface targets and give accu-rate ranging. Success largely depended on valve techniqueand by then we could produce several hundreds of kilo-watts of pulsed power at frequencies of the order of100 MHz. The first experimental model (Type 281)delivered 1250 kW. This set was produced by June 1940and installed at Eastney Fort East. On 11th July the firstair raid on Portsmouth was made. It occurred about 6 pm.At 5.30 pm we were plotting the aircraft approaching fromCaen and from the west of the Isle of Wight.

The first ship to be fitted with type 281 was HMS Didoin October 1940 and the second HMS Prince of Wales inJanuary 1941. These sets had been made in Signal Schoolworkshops. Delivery from contractors began in February1941. The performance figures are given in Table 3.

Table 3: Performance figures of Type 281

Power output: pulse length = 15 /JS 350 kWpulse length = 2.5 //s 1000 kW

Range against medium and high aircraft60-110 mile (96-177 km)

Range against battleships 22000 yard (20.1 km)Bearing accuracy 1°

It is fitting to note here that the aerial system of Type281 was developed from the results of experimental aerialarrays tried out in HMS Carlisle using an Armyequipment GL1 adapted for ship use. This was done toobtain information with particular reference to AA rangingin anti-aircraft cruisers. Much useful data was forthcomingfrom these experiments and Carlisle was successful in theRed Sea after the entry of the Italians into the war.

In August 1940, during tests of an RAF set fitted in aWalrus aircraft on the slipway at Lee-on-Solent shippingwas detected at a range of about five miles. As a result ofthis Type 291 was produced operating on a frequency ofapproximately 240 MHz for fitting into destroyers. Thisset gave good surface results, 17000 yard (15.5 km) againstcapital ships and 6000 yard (5.5 km) against a surfacedsubmarine.

As already mentioned, the group under Coales had beenworking since 1938 on frequencies of the order of600 MHz. At the end of 1939 trials had given encouragingresults. At the AA Range, Eastney, ranges of 10000-12 000yard (9140-10970 m) on aircraft had been consistentlyobtained. An experimental set in HMS Nelson when fittedon the main armament director detected a convoy at30000 yard (27430 m). In the final models the averageresults under normal conditions were 18000 yard(16460 m) range against a cruiser and 12000 yard(10980 m) on a destroyer.

This series of Radar outfits (Types 282/4/5) were widelyfitted in the Royal Navy during the war, and materiallyassisted in the successful actions against the Bismarck andScharnhorst.

Although work in the 600 MHz spectrum band wasregarded as the most likely to produce positive results in1938, it was nevertheless realised that much higher fre-

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quencies would have very important applications if theycould be used reliably and effectively. Experiments in the3000 MHz band were begun both in Signal School and inthe GEC Research Laboratories at Wembley. There wasan urgent need for a set suitable for night fighters. It wouldhave to operate on very high frequencies to enable aneffective aerial system of sufficient gain to be designed forinstallation in the very limited space available in such air-craft. Frequencies of this order also held promise ofimproved results against surface vessels.

6 Type 271 radar

In 1940, the perfecting of the velocity-modulated tube atthe Signal School Laboratory Bristol and the greatlyimproved performance obtained from the GEC magnetronenabled rapid progress to be made at the Air MinistryResearch Laboratory Swanage; by the end of the year verystriking results from trials were achieved.

A group under S.E.A. Landale went to Swanage tostudy the techniques, and, at the end of December 1940,they returned to Eastney with a replica of the Swanageapparatus. Experimental work continued at Eastney and itwas decided to build a set for a corvette.

The main objective was to produce a set as quickly aspossible. Anything which could assist in defeating theU-Boat menace which was then reaching its peak was ofvital importance and not the least difficulty in producingthis equipment was to design an effective aerial system.The requirements were for an aerial which could betrained on any bearing capable of giving a sufficiently con-centrated beam to give reasonable accuracy and of suffi-cient width in elevation that the beam would not roll offthe target when installed in a corvette, a class of shipwhich would roll heavily in Atlantic conditions. Further,the aerial had to be so designed that it could operate in theroughest weather. It was discovered that we could acquire24 old Chadburn pedestals used for D/F loops in the Mer-chant Navy. These were acquired and the aerial wasdesigned to give a beam of about 1° in azimuth and 20° inthe vertical plane. Early in March 1941, this apparatus wasinstalled in HMS Orchis and on 25th and 26th March theresults given in Table 4 were achieved.

Table 4: Results achieved on HMS Orchis

12000 yard HMS Ambuscade5000 yard Small submarine surfaced2800 yard Small submarine trimmed down1300 yard Small submarine periscope 8 ft extended

Our optimism was justified and the results were goodenough for the experimental design to be repeated withonly minor improvements for greater reliability because ofthe strenuous conditions at sea under which the equipmentwould have to operate. It was decided to build 12 sets atthe Eastney laboratories as quickly as possible and afurther 100 were ordered from Allen West, Brighton, whocopied our models. The 12 sets were completed by the endof June 1941 and, with those which were beginning to bedelivered from Allen West, 25 ships were being fitted bythe end of July of that year.

This was a period of great enthusiasm and hard work atEastney. It was also the period when Portsmouth was suf-fering the worst of its air attacks. Apart from cracked wallsand many broken windows, the laboratories received nosignificant damage. It was, of course, a period of strain andit was always a relief each day to have everyone turn upfor duty.

The successful development of the first centimetricequipment was only the beginning. This type of radar(Type 271) was further developed with parabolic mirrors,higher powered magnetrons, aerial systems which could bestabilised in azimuth and elevation and the application ofwaveguide techniques. In 1942, Type 277 was developedand fitted in frigates and above, with common transmittingand receiving aerials capable of rotation in either directionfrom two to 15 rev/min stabilised in azimuth and elevationand with magnetrons capable of giving up to 500 kWoutput. This was the last set of importance which wasdeveloped and installed to the Fleet in any quantity duringthe war. A summary of the results obtained on trial isgiven in Table 5.

Table 5: Results obtained on trial of Type 277

Range Battleship/BattleshipBattleship/SubmarineFrigate/BattleshipFrigate/Submarine

47 000 yard22000 yard36 000 yard13 000 yard

When laid on the horizon aircraft at 1000ft weredetected up to 40 mile.

In 1941 work began on a radar outfit which becameknown as Type 274. Its frequency was in the 3000 MHzrange and the aerials were mounted on the main arma-ment director. Later, work of a similar nature was begunon equipment for the HA director and the design com-pleted though complete development did not occur untilthe war had ceased. These two designs were the basis ofthe equipment which was later installed in aircraft carriers.By the end of 1943 the increasing complications of theequipment needed to meet the staff requirements togetherwith the difficulties arising from material shortages andconflicting priorities combined to extend the time taken tocomplete a project.

7 Development of radar in the last two years of theWar

During the last two years of the War progress was madeon the development of radar at even higher frequencies.Designs were produced for apparatus to be attached to

STAAG mountings, which would range on and follow thetarget automatically. The frequencies used were in the10000 MHz band. Admiralty Signal Establishment Exten-sion, Bristol, moved to Baldock in 1944 and became theServices Electronic Research Laboratory. Investigations inthe region of 30000 MHz were undertaken and amongstother developments were valves for proximity fuses.

There were many commitments which had to beaccepted and completed in addition to the main prog-rammes. One was to design and produce a complete radardetecting system, including the hut in which it had to beinstalled for Iceland. This was eventually erected at Reyk-javik in 1944. I have made no mention hitherto of themany problems associated with the display and thepassing of information to the various offices in a ship. Thisdeveloped from the simple A-scan tube in the originalType 79Y set installed in HMS Sheffield to the complicatedequipment required in the fire control centres and in thecontrol rooms in aircraft carriers. Much of the present dayapparatus used in the control of guided weapons whetherused for tracking, guiding or homing owes its origin towork undertaken between 1935 and 1945.

It may be of interest to note that the numbers engagedon radar research and development at the AdmiraltySignal Establishment was about 25 in 1939 and at the endof the war had risen to over 900.

Before concluding, I should like to refer to the install-ation of Type 79Z at Fort Wallington, Fareham. Weinstalled this in July 1940, after the surrender of France; itwas placed there to assist in the passing of information ofthe approach of enemy aircraft in conjunction with thatderived from the Chain Stations. Both Ventnor and Polingstations were temporarily put out of action in August 1940and Fort Wallington was at that time the only radarstation working in the Portsmouth area. We also hadsimilar equipment at Eastney Fort East which by then waslargely used for instructional purposes. This acted as astandby for Fort Wallington and the information wereceived was passed to Fort Wallington by phone. Regularwatches were kept every night and both the operators andthe experimental staff who were on fire-watch dutiesobtained useful experience and interest in plotting thecourse of enemy aircraft during the raids and under realand not simulated conditions.

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