The History of Air Intercept Radar & the British Nightfighter 1935–1959

Ian White

• Publisher: Pen & Sword Aviation
• Year: 2007
• ISBN:
  9781526743466
• Topic: History
• Subtopic: Military & Maritime History
• Index: History

This detailed history of Air Intercept radar traces the development of this vital military technology with the Royal Air Force during WWII. In the years after World War I, the United Kingdom was desperate to develop some form of protection from an enemy air strike. As early as 1923, the British Army had devised "sound mirrors" that could detect aircraft up to twelve miles away. This technical history traces the development of military radar technology from this early, experimental phase to the creation of the first air-to-air radar systems and their uses in battle. Historian Ian White sets this fascinating narrative within the larger political, military, economic and technological context of the era. Through World War II, Air Intercept radar was a vital asset in protecting RAF bomber forces as well as the country itself. But developing the technology required the tireless work of physicists and engineers in the Air Ministry Research Establishment, particularly members of the Establishment's Airborne Group working under Dr. Edward Bowen. Their Airborne Interception radars, such as the AI Mk. IV, were used in Blenheim night-fighters during the winter Blitz and by Mosquito during the Baedeker Raids. This in-depth history covers the introduction of centimetric technology at the Telecommunications Research Establishment, the creation of centimetric AI, and their installation in the Beaufighter and later marks of the Mosquito. It describes the creation of the Radiation Laboratory at MIT and concludes with a section on further developments during the Cold War.

CHAPTER ONE

The Electronic Solution

1930–1937

Having been advised by the Air Staff in 1925 that there was no known defence against air attack, the British Government placed an increasing reliance on universal disarmament and the League of Nations,1 as instruments of international security. These factors conspired to induce a malaise within the country, which accepted that bombing was indefensible, and caused many people to repudiate war and the armed forces that waged it. To some extent the RAF was responsible for this situation. It was their proposition that a defence against the manned bomber was not feasible, and the only means by which Britain might be protected lay in the field of massive retaliation. This policy, sometimes referred to as the ‘knock-out blow’ or ‘counter-bombing’, was to feature prominently in Air Staff doctrine and Government thinking throughout the 1920s.

By the time of the opening of the League of Nations conference on World Disarmament, in February 1932, the fear of air bombardment, fuelled by politicians and writers of fiction,2 had reached manic proportions. Five days before the opening of the Conference, fighting broke out in Manchuria between China and Japan, from where newsreel film and photographs showed the appalling destruction of Shanghai by Japanese bombers. Stanley Baldwin, the Lord President of the Council in Ramsey MacDonald’s Government of National Unity,3 was deeply shocked by the images and later described them as a ‘nightmare that would not fade’. The failure on the part of the League of Nations to act decisively against Japanese aggression, induced Baldwin to make his infamous statement in the House of Commons on 10 November 1932:

I think it is well also for the man in the street to realise that there is no power on earth that can prevent him from being bombed. Whatever people may tell him, the bomber will always get through. The only defence is offence, which means you will have to kill more women and children more quickly than the enemy if you want to save yourselves.4

By coincidence, or by design, Baldwin’s assertion that ‘the bomber will always get through’, complied exactly with the Air Staff’s policy on retaliation and reinforced the RAF as a bomber oriented service. From the public’s viewpoint, the statement fuelled the civilian’s fear of bombing and raised the prospect of ‘appeasement’ as the only means to prevent widespread devastation. Therefore, by the end of 1932, the Government, the Air Staff, and the alarmists, were pulling roughly in the same direction. In the meanwhile, the British Government continued to press for international disarmament at the Geneva Conference. However, since neither the United States (US), nor the Soviet Union, belonged to the League of Nations, the proposals to outlaw aeroplane bombers came to nought. Accordingly, the Conference was abandoned in November 1934, having done little to reduce the arms race or prevent war.

1922–1933

Until the late 1920s, France was regarded as Britain’s principal ‘enemy’, as far as the air defence of the United Kingdom (UK) was concerned, and the direction from which any attack was most likely to come. To this end, as during the First World War, the Government continued to sponsor the development of sound locators. In 1922, an experimental station run by the Army was moved from its location at Joss Gap, near Dover, to The Roughs, near Hythe, where a 20 feet (6 metre) diameter sound ‘mirror’, built as a solid concrete casting, was set against the cliff face. With the sound collected at the mirror’s focus and piped by an elaborate stethoscope to a collocated observer, the system was declared operational during the early months of 1923 and, in September, detected an aircraft at a range of 12 miles (19 km).

In 1925, Dr W.S. Tucker was appointed as the Director of Acoustical Research and two years later proposed the installation of a chain of 20-feet sound mirrors along the south coast. Only two were completed, the first at Abbott’s Cliff, near Dover, and a second at Denge on the Dungeness peninsula. Before these were completed in 1928, Dr Tucker finalised the design of a more sophisticated 30 feet (9 metre) mirror, that incorporated the lessons learned from the previous experiments. Angled slightly upwards and with more protection for the operating staff, two of the new mirrors were built at Hythe and Denge and completed by the spring of 1930. On trials the mirrors demonstrated a range capability comparable to the 20-feet version, but did show an improvement in accuracy, especially in the vertical plane.

Tucker’s final design was intended as a long-range device and since the targets would be approaching at low angles of elevation, the height of the mirror was reduced to 26 feet (8 metres), but increased in length to 200 feet (61 metres) with a curvature of 150 feet (46 metres). The instrument’s size precluded the use of stethoscopes, so twenty static microphones were employed to catch the sound. One example of these giant mirrors was built at Denge in 1930, and employed, along with the others, in the annual air defence exercises until 1935. In 1932, the 200 feet mirror detected aircraft at 30 miles (48 km), when the unaided ear could only manage 5½ miles (8 km). Although a Thames Estuary scheme was proposed by Tucker and approved, the order was cancelled and no work was undertaken in light of the developments in radar.5

From 1933 onwards, however, France, through the neglect of her armed forces and the transition towards a static defence, had fallen by the wayside in the bomber race and passed the mantle to its erstwhile enemy, Germany. Although banned from maintaining bombers and submarines under the terms of the Versailles Treaty, Germany nevertheless established the beginnings of a clandestine air force, the Luftwaffe, within the small Army (Reichswehr) permitted by the Treaty. With secret Government funding and the active co-operation of the Soviet State, and through the sponsorship of civil aviation and sports flying, Germany was able to recreate the basic structure of an air force by 1930.

With the appointment of Adolf Hitler as Chancellor in January 1933, Germany embarked on a programme of rearmament and industrial expansion and established a foreign policy based on the reclamation of land lost during the First World War. In all three areas the emerging Luftwaffe was destined to play a significant role. With Herman Goering at the head of a new Air Ministry (Reichsluftfahrtministerium – RLM), the Luftwaffe was established covertly during 1933, with the ex-general manager of the state airline, Lufthansa, Erhard Milch, as the State Secretary responsible for organising the new arm and Generalleutnant6 Walter Wever, as its first Chief of Staff and the custodian of its doctrine and strategy.

In 1933, the response in Britain to the possibility of the re-emergence of a rearmed Germany, was, on the whole, greeted with scepticism by Parliament and public alike. Nevertheless, Baldwin’s warning on the possibilities of strategic bombing was particularly relevant to Britain in two respects. First, the country’s geography placed the major conurbations and much of its industry within 70 miles (113 km) of the coast and, second, the improvement in the speed of bombers was beginning to erode the fighter’s performance advantage.7 By 1933, the margin of safety had very nearly reached zero and had thus dramatically reduced the period during which the bomber could be intercepted and destroyed before reaching its target.

1934

In these circumstances, the need for some form of early warning mechanism to alert the defences to an impending attack, coupled with the availability of fast climbing fighters, was of paramount importance to the country’s survival. These criteria were ably demonstrated during the 1934 air defence exercises, held during the late summer, which took the form of night attacks on London, and ironically, Coventry, as it was one of the country’s most important industrial targets. The exercises amply demonstrated Baldwin’s theory, when only two out of every five bombers were intercepted, even though they were required to fly with their navigation lights switched on, and on the last night when half the raiding force reached their targets unmolested.

In reality, however, the Luftwaffe’s strength was less than the Government supposed and its bombing capability was almost non-existent against the shorter-range European cities, let alone London. Whilst Germany possessed relatively large numbers of aircraft, few of them were formed into cohesive units and many were deficient in operational equipment. In 1934, therefore, the Luftwaffe might best be considered more a collection of pilots and aeroplanes, than an effective air force. Faced with the RAF, whose equipment, experience and organisation was more effective, Britain’s position was exposed, but not desperate. Provided the country looked towards its defences, the situation was redeemable.

The results of the 1934 exercises prompted the Air Officer-in-Chief (AOC-in-C) of the Air Defence of Great Britain (ADGB), Air Marshal Sir Robert Brooke-Popham,8 to agree to the formation of a special sub-committee of the Committee of Imperial Defence (CID), to examine the strength of London’s defences. Earlier that year, a junior scientist, Dr A.P. ‘Jimmy’ Rowe, the Personal Scientific Assistant to the Air Ministry’s Director of Scientific Research (DSR), Dr Harry Wimperis, although barred from becoming involved in radio or armaments research, undertook a thorough search of the Ministry’s files to see what references were available on air defence. Rowe’s trawl unearthed fifty-three files, which showed that whilst the RAF had expended some considerable effort on the design of fighter aircraft, they had neglected to apply scientific analysis to the problem of air warning. Rowe submitted his report to Wimperis, with a recommendation that an approach be made to the Secretary of State for Air, Lord Londonderry, advising him that unless some method of early warning be developed, the country stood a very good chance of losing the next war, if it began within the following ten years!

Interest in the air defence problem outside Government circles was broadly confined to Winston Churchill and his scientific advisor, Professor Frederick Lindemann,9 who considered the adoption of a defeatist attitude in the face of any threat, without an examination of the scientific alternatives, to be short-sighted. To this end, he proposed the whole of the Government’s not inconsiderable scientific resources be made available to resolve the issue.

Pressure from these groups was eventually brought to bear on the Secretary of State for Air to find a solution. On 12 November 1934, Wimperis drafted a document in which he reviewed current technology, including an outline of the transmission of radio energy ‘along clearly defined paths’, and proposed that a group of scientists be formed to assess and evaluate the possible alternatives. Since the Admiralty and the War Office had an interest in Anti-aircraft (AA) problems, Wimperis recommended that the group be established under the auspices of the CID, on which he would sit and represent the Air Council’s interests. Wimperis’ paper, forwarded to Lord Londonderry, the Chief of the Air Staff (CAS), Marshal of the RAF (MRAF) Sir Edward Ellington,10 and Sir Christopher Bullock, the Permanent Secretary at the Air Ministry, may rightly be considered as the document that brought radar into being.

Londonderry approved Wimperis’ paper in late November, and formally invited Professor Henry Tizard of Imperial College, London,11 to chair the group that would ultimately comprise himself, Professor A.V. Hill12 of London University, Professor P.M.S. Blackett13 of Birkbeck College, London, Wimperis and Jimmy Rowe as secretary. The first meeting of what was entitled ‘The Committee for the Scientific Survey of Air Defence’, but better known today as ‘The Tizard Committee’, was scheduled for 28 January 1935.

In the meanwhile, Wimperis contacted the Superintendent of the Radio Research Laboratory at Slough, Mr Robert Watson Watt,14 and invited him to the Air Ministry on 18 January to discuss the feasibility of ‘death rays’. Following the meeting, Watson Watt returned to Slough and tasked his assistant, Arnold Wilkins,15 to calculate exactly how much radiated power would be required to raise the temperature of a given quantity of water, to a stated level, at a stated distance. Prior to undertaking the calculation, Wilkins noted the initial ...