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The Dowding System

Page history last edited by Alan Hartley-Smith 1 month, 2 weeks ago

Military Early Days

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Introduction

This bears its name as being the brainchild of Air Chief Marshal Sir Hugh Caswall Tremenheere Dowding that enabled the Royal Air Force with more limited resources in 1939 at the start of WWII to defeat the intention of the much larger Luftwaffe to clear and command the skies over the English Channel and United Kingdom, a prerequisite to Operation Sealion, Hitler's invasion plan. 

 

The solution was to bring science into the arena, and comprised two areas of technological developments - the new ability to detect the incoming enemy bombers and their fighter escorts sufficiently early together with the ability to then get the defending fighters into position in time to destroy them in sufficient numbers. Among others Marconi was extensively involved in both areas based on its work on radio telephony during the First World War and its capabilities in research and engineering in wireless and television and management of large-scale systems. In the modern era through mergers in the now electronics industry virtually all of the other companies involved became part of the Marconi group and therefore are included in this wiki. In point of fact there was also a third arm, a nation-wide installation of addition telephone lines by the General Post Office, itself alone a massive undertaking.

 

The Dowding System  1.  2.

The genesis of this is a complex story and and covers a long period of time - there are several books (see reading list below) which cover it in great detail, but for the present purpose it is useful to have just a summary of the main points.

 

The first aerial bombing of England was in 1914 and continued through until 1918. This resulted in the creation of the world's first strategic air defence system, the design of which influenced the work throughout the 1920s and 30s, and featured the use of aerial radio telephony, and the development of a central command structure to gather and disseminate information to regional control rooms with plot spotting on a map. A very interesting description is available here. However, the general feeling at the time was summed up in a statement by Stanley Baldwin "..... the bomber will always get through"  Notwithstanding, work continued including the formation of an organisation "Air Defence of Great Britain" or ADGB to coordinate air defensive and offensive forces. In 1924 the then new Royal Air Force created a Directorate of Scientific Research whose first Director was Henry Wimperis, who came to learn of the work of Robert Watson Watt on ionospheric radio research at the National Physical Laboratory. Wimperis formed the Committee for the Scientific Survey of Air Defence (CSSAD) (also known as the Tizard Committee as he was the Chairman) and his immediate superior was Air Chief Marshal Dowding. Dowding had served in World War 1 and had direct experience of aerial combat so was well aware of the difficulties encountered. During the 1920s and 1930s he served in a variety of service and government posts and became Officer Commanding the RAF Fighter Command, so through CSSAD he was able to initiate the funding for the work which culminated in the development of the Chain Home radar system. In parallel there was continuing work on the technology of wireless direction finding, including the Biggin Hill Experiment and other trials, which greatly increased the accuracy and speed of position determination of the fighters using the Pip-squeak navigation system, together with the development of a method of identifying friendly aircraft, IFF, and incidentally stimulated the development of airborne radar for final interception. Dowding was therefore able to combine these activities together with the enlarged telephone system, the existing Observer Corps, and the new discipline of operational research which enhanced the multiple control room method to create the "Command and Control" system that enabled him to direct fighters onto German attacks; taking advantage of fighting above Britain's home territory allowed the RAF to deny Germany air superiority, saving the UK from possible German invasion and dealing the Axis a major defeat early in the Second World War by winning the Battle of Britain.

 

In 2020 a celebration of the 80th anniversary was held and some events are detailed here

 

See the modern manifestation of the system Headquarters here

 

The memorial in Westminster Abbey

 

A comprehensive description of the extensive studies and actions carried out during the 1930s that enabled this result can be found in the Radio chapter of "The Narrow Margin". 

 

A broad description of the whole Radio Warfare scenario is given in this postwar Technical Staff Monograph also here

 

This is an extract from Dowding's official despatch which goes into great detail of all aspects of the Battle.

 

Battle of Britain Historical Society

 

BOBHSOC

 

Entry on IWM site

 

Duxford note

 

The Technologies

 

Editors note - the acronym "RDF" originally applies to the classical technology "Radio Direction Finding" but it also became shorthand for the new technolgy of "Radar", by analogy, to conceal its real function. 

 

Radar

This was the new detection development, in particular the creation of the Chain Home series of radars which, as part of the central topic of this wiki, is already covered in detail here. From this initial military inception postwar radar continued to develop in both defence and offence applications and also moved into the civilian arena through air traffic control, which is also covered in the wiki.

 

In the original Dowding system of fighter control, information from the Chain Home coastal radar stations was relayed by phone to a number of operators on the ground floor of the "filter room" at Fighter Command's headquarters at RAF Bentley Priory. Here the information from the radar was combined with reports from the Royal Observer Corps and radio direction finding systems and merged to produce a single set of "tracks", identified by number. These tracks were then telephoned to the Group headquarters that would be responsible for dealing with that target. Group would assign fighter squadrons to the tracks, and phone the information to Section headquarters, who were in direct contact with the fighters.

Because the Chain Home radar stations faced out to sea, once airborne intruders had crossed the British coast they could no longer be tracked by radar; and accordingly the interception direction centres relied on visual and aural sightings of the Observer Corps for continually updated information on the location and heading of enemy aircraft formations. While this arrangement worked acceptably during the daylight raids of the Battle of Britain, subsequent bombing attacks of The Blitz demonstrated that such techniques were wholly inadequate for identifying and tracking aircraft at night.

 

Experiments in addressing this problem started with manually directed radars being used as a sort of radio-searchlight, but this proved too difficult to use in practice. Another attempt was made by using a height-finding radar turned on its side in order to scan an arc in front of the station. This proved very workable, and was soon extended to covering a full 360 degrees by making minor changes to the support and bearing systems. Making a display system, the "Plan Position Indicator" (PPI), that displayed a 360 degree pattern proved surprisingly easy, and test systems were available by late 1940.

Starting in 1941 the RAF began deploying production models of the GCI radar, first with expedient solutions, and then permanent stations. Unlike the earlier system where radar data was forwarded by telephone and plotted on a map, GCI radars combined all of these functions into a single station. The PPI was in the form of a 2D top-down display showing both the targets and the intercepting night fighters. Interceptions could be arranged directly from the display, without any need to forward the information over telephone links or similar. This not only greatly eased the task of arranging the interception, but greatly reduced the required manpower as well.

As the system became operational the success of the RAF night fighter force began to shoot up. This was further aided by the introduction of the Bristol Beaufighter and its AI Mk. IV radar which became available in numbers at the same time. These two systems proved to be a potent combination, and interception rates doubled every month from January 1941 until the Luftwaffe campaign ended in May.

 

High Frequency Direction Finding

Input by Malcolm Mack

Introduction

High Frequency Direction Finding, usually known by its abbreviation as HF/DF or colloquially Huff-Duff, is a type of Radio Direction Finder (RDF) introduced for World War II. High Frequency (HF), nominally 3MHz to 30MHz, refers to a radio band that can effectively communicate over long distances, via refraction (bending) of the electromagnetic waves by the ionosphere. There are also VHF and UHF radio bands.

 

HF/DF was one of five main technologies, the others being Radar, Sonar (ASDIC), Signals Intelligence (SIGINT) and Nuclear, that proved critical in defeating the Axis Powers.

 

Early History and WWI

RDF used a radio receiver and antenna system for determining the direction of the source of a radio signal. A direction finder (DF) can be used by an aircraft or ship as a navigational aid. This technique was widely used even before WW1. This was accomplished by measuring the direction (bearing) of at least two transmitters whose locations are already known. When the measured directions from each transmitter are plotted on a map, the intersection of the two plotted lines gives the location of the aircraft or ship carrying the DF. This technique, using the directions to two or more transmitters of known location is called triangulation. Because of the its early use in navigation, the DF was sometimes called a radio compass. Its use as a navigational aid has been almost entirely replaced by more modern navigational systems e.g. GPS.

 

Early DF systems used a loop antenna that could be mechanically rotated. The operator would tune in a known radio station and then rotate the antenna until the signal disappeared. This meant the antenna was now at right angles to the broadcasting station, although it could be on the either side of the antenna. By taking several such measurements, or using other forms of navigational information to eliminate one of the ambiguous directions, the bearing to the broadcaster could be determined.

 

In 1907 an improvement utilising induction coils was introduced by Ettore Bellini and Alessandro Tosi that greatly simplified the DF system in some setups. The Bellini-Tosi direction finder (B-T) was widely used on ships, although rotating loops remained in use on aircraft as they were normally physically smaller.

 

During WW1, Henry Joseph Round who was a Marconi employee before being commissioned, set up a chain of direction-finding stations along the Western Front. Following their success another set of stations were set up in the UK, and these detected the move of the German High Seas fleet from Wilhelmshaven before Jutland in May 1916. A very comprehensive description of a typical Naval Station is here

 

Inter-war Years

After the war in 1921 H.J. Round became the Chief Engineer for the Marconi Wireless Telegraph Company, where he was heavily involved with the first wireless broadcasts. He eventually left to form his own consultancy, but was called upon to be a member of the Sonar (ASDIC) steering committee in WWII.

 

Following WWI, and the work that he had carried out as a commissioned officer during this period, Frank Adcock raised his patent in 1919 on the design of the Adcock array; based on the use of 4 monopoles or dipoles arranged in an orthogonal pattern. This was a method of amplitude comparison to determine the direction of arrival of radio signals.

 

Further progress on HF transmission was achieved in 1923 and 1924 when Guglielmo Marconi and Charles Samuel Franklin carried out experiments from Poldhu Wireless Station in Cornwall and Marconi’s yacht Elettra off the Cape Verde Islands and Beirut at 3MHz and 12.4 MHz respectively.

 

Other experimentation in Direction Finding was being carried out by the Admiralty HM School of Signals at Portsmouth, during WWI and through the 1920s and 1930s, with changes in antenna shapes and positioning on various types of warships, submarines and land-based systems. The Marconi Wireless Telegraph Company was fundamental in providing Transmitters and Receivers for these systems. Further research work was being undertaken into ionospheric propagation at the Marconi Research Laboratories by personnel such as T.L. Eckersley. Plus improvements in the HF/DF System.

 

In 1925 Robert Watson-Watt, whilst working in the Atmospherics Department of the National Physics Laboratory Radio Section at Ditton Park near Slough, made a breakthrough in the use of the Adcock antenna and an oscilloscope. This work was in the study of lightning strikes, but led to progress in the design of HF/DF. Watt and Herd wrote an extensive paper on the system in 1926, but as the publicity showed it was used for lightning strikes, there was a lack of interest, which allowed the concept to be developed in secret in the late 1930s.

 

Some work on automating the B-T system was carried out prior to the opening of WWII, especially by the French engineers Maurice Deloraine and Henri Busignies working in the French division of the ITT Corporation. The system motorized the indication of the direction. The work was destroyed before the German invasion of France, and the development continued in the USA.

 

WWII

Waclaw Struszynski was the head of the Direction-Finding Division of the Polish state Telecommunication Establishment in 1939 when the country was invaded. He was evacuated from Warsaw and reached England in 1940. His work for HM School of Signals (later called the Admiralty Signals Establishment) proposed a solution to the problem of signal reflection from the ship’s superstructure, but also introduced ‘sense’ into the antenna. He also led a team that developed a practical antenna, which enabled effective HF/DF systems to be installed on Royal Navy convoy escort ships. Struszynski subsequently worked at the Marconi Research Laboratories at Great Baddow, where he was a consultant in communications research. HF/DF was a valuable part of the Allies’ armoury in detecting German U-Boats and commerce raiders during the Battle of the Atlantic.

 

During the rush to install the Chain Home radar systems prior to the Battle of Britain, CH stations were located as far forward as possible, along the shoreline, in order to provide maximum warning time. This meant that the inland areas of the British Isles did not have radar coverage, relying on the Royal Observer Corps (ROC) for visual tracking in this area. As the entire Dowding system of air control relied on ground direction, some solution to locating their own fighters was needed. The ROC being unable to definitively provide this information. The expedient solution was to provide HF/DF Stations to tune into the fighter’s radio through triangulation. To aid this a system known as Pip-Squeak was installed in at least two fighters per section to send out a trackable tone.

 

During the 1930s and 1940s there was an expansion into the VHF and UHF bands for both communications, television and HF/DF techniques.

 

Specially constructed Y-stations across Britain and a number of countries overseas undertook direction finding on wireless transmissions during both WWI and WWII. Thousands of wireless operators especially during WWII, many of them civilians, but also Wrens, WAAF personnel and members of the ATS, tracked the enemy radio nets up and down the dial, carefully logging every letter or figure. The messages were then sent back to the Admiralty Room 40 in WWI, and Bletchley Park (Station X) in WWII. These intercepts were deciphered, translated and fitted together like a gigantic jigsaw puzzle to produce as complete a picture as possible of what the enemy was doing. There was a station at Marconi Research Laboratories at Great Baddow, the organisation being taken over by the RAF and RN for the duration of WWII. Work continued in this period to improve the HF/DF systems and address other perceived threats.

 

Input by Roy Simons

Most of the later wartime DF work was done at Baddow in Section E and Section K in which T.L.Eckersley was the prime mover - he invented the spaced frame system that did not need to be installed on a conducting earth or mat. His staff included  G.Millington, K.Tremellen and S.B.Smith. G.Isted ran the laboratory work of Section E and experimental work in a large hut in the field with WREN assistance. R.J.Kemp ran Section C with R.F.O’Neill, R.G.Waring, D.J.Fewings and me.  Others involved at some time included F.P.Best, J.H.Moon, J.Vickers, S.A.W.Jolliffe, J.S.Forbes. We had a detachment of RAF wireless operator mechanics attached to us to build some equipment etc.  We had a number of flight trials over the site which required a lot of night time working.

 

Earlier DF equipment was designed in New Street over many years and an Adcock system with a Type DFG12 receiver, the latest pre-war version, in which J.F.Hatch was involved, was that used during the war. A later version was the Type DFG24 using a CRT. I developed a VHF automatic version for later detection of V2 missiles in case they had radio guidance but they did not. I do not know if any of the Eckersley spaced frame HF equipments were used in the UK - I know several were used in the desert and in the Far East.

 

There were many more other developments in progress in these early days at Baddow following on from the research carried out at Broomfield, Hall Street and New Street.

 

Just to illustrate how important DF continued to be is shown by this extract from Practical Wireless June 1951:

 

Jet Aircraft Radio at the Festival

A replica of the cockpit of the Comet, the world's first jet airliner, showing its complete Marconi wireless communication and navigational aid equipment will be exhibited in the Transport Pavilion, at the South Bank Exhibition of the Festival of Britain. This Pavilion houses not only exhibits of great historical value, showing the development of transport and communications, but also some of the most up-to-date equipment. . The Comet equipment consists of two high-power high-frequency transmitters, two high- and medium-frequency high-discrimination receivers and two automatic direction finders. Voltage regulators for this installation are also of Marconi design and manufacture.

The Comet is also fitted with Marconi suppressed aerials which do not protrude above the skin of the aircraft but which are built into the structure as an integral part of aerodynamic design. One of the greatest aeronautical advances of today is embodied in this new technique which also embraces the loop aerials associated with the automatic direction finder. All that is necessary to navigate with the automatic direction finder is for one member of a crew to tune the receiver to any transmitting station. Bearings of that station can then be read off, continuously and instantaneously, by members of the  crew. Repeater bearing indicators and receiver control boxes can be installed and repeated at any crew position.

Visitors to the Festival will thus be able to see a vital part of one of the world's greatest aircraft.

 

Reading list

Dowding of Fighter Command - Vincent Orange - Grub Street

Tizard - Ronald Clark - Methuen

RDF1 - Michael Bragg - Hawkhead

BUILDING RADAR - Colin Dobinson - Methuen

Britain's Shield Radar and the Defeat of the Luftwaffe - David Zimmerman - Amberley

The Narrow Margin - Derek Wood and Derek Dempster - Tri-Service Press

Direction and Position Finding by Wireless (4th ED 1947)- Ronald Keen - Iliffe (Major Keen spent a lot of his time at Marconi)

 

Other online references 1.

 

 

Military Early Days 

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