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Chapter 1: Retrenchment and Air Defence (1918–1932)


AT A quarter past eleven on the morning of the first Sunday in September 1939, the Prime Minister, Mr. Neville Chamberlain, announced in a broadcast to the nation that Great Britain was at war with Germany for the second time within a generation. In the course of a brief speech he reminded his audience that there were worse things than war; but his tone bore witness to a keen awareness of the evils that war would bring. Mr. Chamberlain was known to have longed ardently for peace; and his voice seemed that of a tired man, at least temporarily cast down by the knowledge that all his efforts to secure what he had set his heart upon had failed to achieve their purpose.1

It seems safe to assert that the Prime Minister’s lack of enthusiasm for the tasks which German intransigence had forced upon the country were shared by at least the majority of its inhabitants. In the national mood there was none of the elation which, twenty-five years earlier, had led to patriotic demonstrations accompanied by expressions of the hope that a reluctant government would not condemn the country to an inglorious peace. To men and women keenly alive to the horrors and privations of the last war and its aftermath, the coming struggle promised only greater horrors, worse privations and an uncertain outcome.

A few minutes after Mr. Chamberlain had finished speaking, the ‘warbling note’ of the air-raid warning signal was heard in London and many other parts of the United Kingdom, including Scotland. Among the emotions which the sound provoked, surprise can scarcely have played much part, since for years past writers and speakers had predicted that the next great war would begin with a devastating air assault on this country and especially on the capital. British statesmen, moved either by enthusiasm for policies which promised avoidance of war, or by a simple desire to warn the public of the dangers they might run, had not always concealed the dismay

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with which the prospect filled them. As it happened, the United Kingdom was provided with a system of air defence potentially far superior to that possessed by any other country, though as yet it fell short of completeness; but the general public knew little of its merits, had heard much of its shortcomings, and were not unreasonably sceptical of its ability to protect their lives and property in the event of such an onslaught. Accordingly many Londoners, taking up the gas-masks which were their sole portable armour against the threatened hail of high-explosive bombs, prepared themselves, as best they might, for the spectacle of a vast city crumbling into ruin.

In the light of after-knowledge, it is quite clear that these fears were premature and much exaggerated. As we now know, the German Government had no intention of launching an immediate assault on London. So far as the United Kingdom was concerned, the only warlike measures which they sanctioned on or before the outbreak of hostilities were attacks on ships and naval harbours, coupled with the laying of mines in British coastal waters.2 Their military advisers, though indeed attracted by the policy of ‘strategic bombing’ adopted by the British Air Staff and publicised by the Italian General Douhet and other writers on air warfare, had been led by recent experience in Spain to modify their outlook, so that for the present they tended to regard their air force chiefly as a means of clearing the way for an advancing army.3 The warning which came pat on Mr. Chamberlain’s announcement was not occasioned by an oncoming German striking force, but by a harmless passenger machine of whose approach the appropriate authority had not been warned. Yet so firmly did many people in this country expect the enemy to follow the predicted course that, when cancellation of the warning followed an interval unpunctuated by any hostile demonstration, their relief was tinged with an uneasy wonder which was anything but reassuring.

To trace the origin and development of this attitude on the part of the British public as a whole is a task which scarcely lies within the context of this volume. How far it was shared by those responsible for shaping the national strategy, to what extent it influenced their actions and how far, if at all, preoccupation with one form of potential attack diverted attention from other dangers, are, on the other hand, questions which the historian of home defence must certainly consider. And as these questions are linked with issues of long standing, we must begin by retracing our steps at least as far as the years when attention was first paid to the problem of reshaping the national strategy after the First World War.

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At the end of the First World War the British Army numbered about three million officers and men; the Royal Navy had at its disposal more than four thousand ships and small craft, including some sixty battleships and battle-cruisers; and the newly-autonomous Royal Air Force mustered a first-line strength of some three thousand aircraft and had more than twenty thousand aircraft in reserve.4 Almost from the beginning of the century fear of invasion had exercised the minds of British strategists much as fear of air attack was to exercise the minds of their successors; and this preoccupation had markedly affected the disposition of the country’s armed resources during the greater part of the war period.5 From 1914 until the spring of 1918 the United Kingdom was guarded not only by an elaborate system of naval patrols and local naval defence schemes, the whole backed by the powerful Grand Fleet in Scottish waters, but also by an army numbering between three hundred thousand and half a million men.6 About a third of these formed a strategic reserve or ‘Central Force’, while the rest manned fixed defences and provided local guards. In addition the home defence establishment at the close of hostilities included sixteen squadrons of fighter aircraft, 480 anti-aircraft guns and 706 searchlights, the whole endowed in recent months with a system of centralised control akin to that familiar to a later generation. Without its aid—for German air attacks had ceased before its introduction—the air defences had succeeded in accounting for about one in twenty of the hostile aircraft that came within their reach.

By the middle of the war a number of serving officers and others had begun to think—and sometimes to say—that the forces deployed to meet the risk of seaborne attack on the United Kingdom were excessive; and when it was over, German military historians declared that invasion in face of British naval power was at no time seriously contemplated by their country’s High Command. The fact remains that, from 1914 until a few months before the Armistice, no substantial transfer of troops from this country to France or any other foreign theatre was sanctioned by the responsible authorities until the needs of home defence had been considered.*

For obvious reasons, the bulk of the resources assembled by the nation to fight the war did not long survive its close. Once the Armistice was signed, huge armaments ceased to be an asset and became a burden which, alike on social, financial and economic grounds, could no longer be supported. With few exceptions, the members of a

* Robertson, Field-Marshal Sir William, Soldiers and Statesmen 1914–1918 (1926), Vol. II, p. 8.

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Citizen Army were eager to return to their peacetime jobs before they were supplanted; and a country dependent for half its food on imports only to be paid for by a thriving export trade in goods and services had every reason to beat swords into ploughshares as rapidly as possible. That, even so, there was something to be said for the retention of a substantial army for home defence, and of a system of air defence capable of affording a security analogous to that provided by the peacetime navy, was not unknown to statesmen of the day; but little support for such measures could be expected from an electorate eager to taste the fruits of victory. Moreover, much was hoped from the ill-fated League of Nations, which might make arms unnecessary by settling international disputes without recourse to war.

In the outcome, the process of demobilisation and retrenchment which followed the Armistice not only swept away most of the additions made to the country’s armed strength in the past few years, but also threatened the underlying fabric of establishments authorised in time of peace. For a country like Great Britain, concerned not merely to guard her homeland but also to protect a widespread Commonwealth or Empire, the assessment of her military needs was a complex problem, which sometimes led to paradoxical solutions. Thus it was accepted that, in time of peace, the strength of the army retained in the United Kingdom must be governed as a rule by the need to maintain reliefs for garrisons abroad, and only exceptionally by reference to any situation likely to arise at home. It follows that, while encroachments on the home defences in the post-war years could be upheld on the ground that invasion and seaborne raids were exceedingly unlikely—and while in practice the deciding factor was usually the extent to which successive governments were willing to impose taxation for unwelcome purposes—where the army was concerned their logical justification was the absence of any major threat to the Dominions and dependencies, coupled with the readiness of some of them to take an increasing share in their own defence.

The fact remains that, for some years after the collapse of Germany, a direct assault on the United Kingdom by seaborne forces could be virtually ruled out; and, reasonably enough, the Allied victory was followed by a massive reduction of the forces more specifically intended to meet that contingency. Within a few months of the Armistice, thousands of yards of barbed wire erected along the South and East Coasts in recent years were torn down, miles of trenches were filled in, and about a hundred thousand Territorials hitherto employed for coast defence were diverted to other duties or disbanded.7 At a few commercial and naval harbours the guns and searchlights comprising the ‘fixed defences’ were retained in the hands of skeleton garrisons assigned to ‘care and maintenance’. In theory the defences so distinguished could be rapidly returned to active service in an

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emergency; but in practice their armament was already on the verge of obsolescence, so that they would be of limited value unless it was replaced or modified in the light of recent developments in naval gunnery. Strong objections to modification or replacement were, however, made not only on the score of expense, but also on the ground that a number of strategists believed that coast-defence artillery had had its day and should be superseded by other weapons. As we shall see in later chapters, the outcome was a long period of controversy, during which the coast defences were neither superseded nor made efficient.

Retrenchment had, however, more far-reaching consequences than impoverishment of the coast defences, awkward though that proved to be when the fear of invasion was revived in 1940. A long-cherished principle of British strategy, never formally abandoned in the postwar period and afterwards reaffirmed in the light of fresh considerations, was that the defence of the United Kingdom would be gravely prejudiced if the Low Countries fell under the sway of a first-class power even potentially hostile to Great Britain. Yet within a few years of the Armistice the British Army found itself so circumscribed by financial limitations that the despatch of a substantial Expeditionary Force to prevent such an occurrence, or assist a Continental ally in doing so, seemed quite out of the question.8 Ultimately such a force was indeed made ready and despatched; but the long years of deprivation did not make its creation any easier, nor did they tend, in the meantime, to foster a resolute diplomacy or a sturdy body of tactical and strategic doctrine. The navy, too—in theory always ready to protect the country against unexpected dangers—was in practice so curtailed by retrenchment that at one stage some ships nominally in full commission could not be fully manned without reservists intended for wartime expansion. Moreover, as we shall see, the grand strategy entailed by post-war diplomacy was such that a crisis at home might well find the bulk of our naval strength in a distant theatre.

As a newcomer with no pre-war peace establishment to serve as a standard for its post-war needs, the Royal Air Force was in some ways still more badly placed than the other services to resist the onslaught of retrenchment. By 1921 its whole strength barely sufficed to meet the needs of the army and navy for direct support, so that nothing remained for independent tasks which its leaders wished to tackle.9 As for the air defences—at that time primarily the concern of the War Office, although the air force was responsible for providing fighter squadrons—they were so vigorously pruned that, within two years of the Armistice, nothing was left of them except a substantial quantity of stored equipment, a small Anti-Aircraft School, and the nucleus of an Anti-Aircraft Brigade (later known as the 1st Air Defence Brigade)

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intended to support an army in the field. By the end of 1920 not a gun or a searchlight was deployed for the defence of London, and not one fighter squadron was specifically assigned to home defence.


In the main, the size and scope of the national defences during the period of rather more than a decade which began with the Armistice and ended with Japanese defiance of British interests at Shanghai were governed by political considerations. These embraced a variety of social, financial and economic factors, besides others not so easily defined. But if, with few exceptions, purely strategic arguments were not decisive in this field, it does not follow that no account was taken of them. Since the early years of the century elaborate machinery for the study and discussion by ministers, service experts and officials of questions of national defence in time of peace had existed in the Committee of Imperial Defence, with its permanent secretariat and sub-committees. In 1919 this complex was once more set in motion, although the main committee did not meet till 1920. In the meantime the first post-war Coalition Government, under Mr. Lloyd George, had adopted, for the purpose of preparing revised financial estimates to meet the sudden cessation of hostilities, the assumption that no measures need be taken in contemplation of a major war involving the British Empire during the next ten years. Whatever its value as a temporary expedient, the ‘ten-year rule’—as it soon came to be called—was worse than useless as a long-term basis for strategic planning, since it begged the question which strategic planning is called upon to answer. Nevertheless so comfortable was the rule to the ears of many whose sense of logic would seem, in this instance, to have been overpowered by their reluctance to face unwelcome issues, that successive governments continued to affirm it implicitly or explicitly until 1932. On the other hand, the rule was seldom applied with the strictness which might have helped to reveal its inherent fallacy.

The first great question—described by Mr. Lloyd George as the most important and most difficult the Committee of Imperial Defence had ever had to face—which arose in the post-war years concerned the future of the navy and of British naval strategy.10 Some critics argued that the big, heavily armed ‘ship of the line’ or ‘capital ship’, which had been the keystone of our naval armament for several centuries, had outlived its usefulness, and that the country would do better to invest its diminished wealth in submarines and aircraft. After hearing evidence from several sources the Government rejected that view, and came to the conclusion that the capital ship remained a

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major instrument of policy.11 But they still had to decide what policy they wished the navy to promote. In 1920 the chief naval powers other than Great Britain were Japan and the United States. Both countries had gained in strength and political importance since 1914; both were manifestly contemplating programmes of naval and commercial expansion which threatened to bring them into conflict, and which separately challenged the supremacy hitherto exercised on the High Seas and in the world’s markets by Great Britain. Of the two, America was financially the stronger and technically the more advanced. Had they applied the traditional touchstone of British policy as their predecessors had done in face of German naval ambitions earlier in the century, the Government could scarcely have avoided the conclusion that they must meet the challenge by building ship for ship with the United States and preparing bases for a possible Atlantic war. But there were a number of objections to that course, of which by no means the least weighty was that the vast resources of a competitor whose growing population would enable her to raise huge sums by taxation made a favourable outcome to such an armaments race unlikely. After long debate the Government decided not to put the matter to the test unless attempts at accommodation failed.12 ln due course, therefore, the country accepted at Washington a naval bargain designed to keep expenditure within close limits, but one which carried a grave risk of conflict with Japan.

The effects on every aspect of the national and Imperial defences, including the home defences, were profound. For the next decade and more, virtually all strategic planning was overshadowed first by the assumption that no major threat would arise for at least ten years, secondly by the belief that the ultimate danger lay in the Far East. Accordingly a problematical Far Eastern strategy had first claim on such sums as successive governments were willing to allot to any far-reaching measure of readiness for war. Chief among the measures contemplated were the construction and defence of a great new naval base at Singapore, and with it the accumulation of stocks of oil intended to enable the Admiralty to send the main fleet to Far Eastern waters with a reasonable assurance that it would be fit to fight when it arrived. In theory, home defence and the defence of maritime trade continued to rank equally as first charges on the navy; but in practice the naval strength available at home if the main fleet went to Singapore would suffice to defend the country only if European navies remained weak or their possessors friendly. Meanwhile, for want of a better yardstick, preparations for home defence were measured in most respects by the admittedly improbable assumption of attack by France, since France was the strongest European power after the defeat of Germany and the collapse of Russia. Reviewing the whole field of national and Imperial defence

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in 1921, the Committee of Imperial Defence came therefore to the understandable conclusion that no comprehensive revision of the army’s plan of home defence was needed.13 And a later ruling that, at worst, the army might have to repel landings by the equivalent of one division scarcely controverted that conclusion.

Such, then, was the prevailing climate of strategic thought during the years when the demands of economy, retrenchment and reform were suffered to reduce the national defences to a level which appears in the light of present knowledge dangerously low. In the circumstances discussion of defensive measures, except in the Far East, was bound to seem unreal. If the only redoubtable European country was France, who had long since abandoned her maritime ambitions and was clearly far more concerned with her eastern frontier than with the fogbound island off her northern coast, there could be little danger in lowered naval and military establishments, obsolescent coast defences and inadequate equipment. And indeed there was no immediate danger in these things as long as that assumption remained valid. The long-term disadvantage of such an outlook was, however, that on the triple pretext that economy was paramount, the threat unreal and the remedy uncertain, measures whose value was not dependent on the direction from which attack might come were postponed until their cumulative cost became prohibitive. Like a man who dreads an annual visit to the dentist, successive governments postponed attention to the coast defences, for example, until their overhaul appeared so great a task that the only course they could contemplate was a further postponement attended by still more drastic penalties.


When the Government adopted the principle that measures of home defence in the post-war period, insofar as they were governed at all by purely strategic factors, should be based on the hypothesis of war with France, they by no means accepted the implication that an armed dispute with the sharer of so many recent trials was even remotely probable. On the contrary, that contingency seemed almost inconceivable. Acceptance of the hypothesis as a working assumption implied no more than recognition that defensive preparations must be measured by some standard, and that the most convenient standard—at least on the short view—was the potential striking power of the nearest and strongest European country. But when the assumption came to be applied to the shaping of the air defences, the process led to some conclusions which had scarcely been foreseen.

For long periods during the lifetime of the first post-war Coalition Government some of the most important functions of the Committee

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of Imperial Defence were entrusted to a Standing Sub-Committee headed by Mr. A. J. Balfour, the former Conservative Prime Minister. Inasmuch as Mr. Balfour had played a leading part in the formation of the Committee of Imperial Defence some twenty years earlier, the choice was appropriate. On the other hand, it could be argued—and was argued by some critics of the Government—that so large a measure of responsibility for national and Imperial defence ought not to be exercised by anyone but the Prime Minister in person.

It thus fell to Mr. Balfour to hear, in the first instance, the case for providing, in peacetime, a system of air defence to take the place of that created during the war years and perhaps too hastily abandoned when the war was over. The issue first arose in consequence of a claim made by the Air Ministry to a bigger share of responsibility for national and Imperial defence than that department had yet undertaken. The dangers of air attack had indeed been considered at least as long ago as 1912, when the decision was made to install a few guns for the defence of naval magazines near Chatham. Later it became clear that not only naval and military establishments but also centres of population must be protected, if only to ensure that the threat of air attack did not disrupt the productive effort of civilians deprived of the moral support which such protection gave, and that the authorities were not unduly hampered in their prosecution of the war by complaints from those whose lives and property might be assailed. The experience of the war showed that aircraft, though their obvious military function was reconnaissance, could in fact be used for a variety of warlike purposes. Among them were the reduction of gun-positions and other purely military targets normally tackled by artillery, and also the bombing of more distant objectives, such as factories and cities, which artillery could not reach. Apart from ethical objections to some of these employments, their expediency was sometimes questioned on grounds of extravagance and uncertainty of aim; but proponents of the bomber had much to say in support of their contentions. Within a year or two the usefulness of the aircraft as a direct means of assailing battlefield targets was widely (but not universally) conceded, though the value of what was called ‘strategic’ bombing of objectives far behind the lines remained a controversial issue.

In 1917 the ‘strategic’ school received powerful support from a memorandum written by Mr. Lloyd George and General Smuts as a corollary to one setting forth the administrative and logistic advantages of an air force separate from the other services.14 The authors, with little experience to guide them and writing undisguisedly in a prophetic strain, foresaw a day when bomber forces might strike decisive blows on their own account, reducing fleets and armies to a secondary

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role. The sequel to the two memoranda was the creation of an autonomous air force, charged not only with the provision of squadrons for the direct support of fleets and armies, but also with that of a ‘strategic’ bomber force for use against such targets as those responsible for the higher conduct of the war might choose. A number of squadrons already earmarked for the bombing of Germany were then raised to the status of a distinct command, under an officer owing allegiance to the Supreme Commander, Marshal Foch, but with power to appeal to the War Cabinet in London.15 The designation ‘independent bomber force’, which was given to this formation, was perhaps unfortunate; for it seems to have led some critics to suppose that the necessity of subordinating the operations of the force to the broad pattern of Allied strategy had not been fully grasped.

The Armistice put an end to the independent bomber force. Nevertheless the Air Staff did not relinquish their opinion that direct support for ships and troops was not the only, or indeed the most important, function of air power. In the controversy about the future of the capital ship which arose some two years later, Air Chief Marshal Trenchard, then Chief of the Air Staff and formerly in command of the independent bomber force, found an opportunity to draw attention to the use that might be made of bombers in a war at sea.16 Soon afterwards he followed up his arguments by asking the Government to entrust to the air force certain specific tasks, including the primary responsibility for defending the home country against virtually all forms of direct assault, whether by sea or air. He did not claim that aircraft alone could repel invasion, but suggested that any ships or soldiers needed might be subordinated to the air force, just as air squadrons were subordinated to fleets and armies when predominantly naval or terrestrial actions were in view.17

The weight of orthodox opinion, coupled with the considered view of the Government that the capital ship was still the mainspring of sea power, soon compelled the Air Staff to abandon the revolutionary proposal that the air force should replace the navy as the principal opponent of an assailant who came by sea.18 There remained the suggestion that they should undertake the duty of repelling one who came by air. Early in the recent war the air defences had been controlled by the Admiralty, but later their supervision had passed to the General Staff, who had performed the task with some success and who now showed little desire to relinquish it. Indeed their view was that, if an Air Ministry was necessary at all, its functions should be confined to the development of civil aviation and the provision of such aircraft or air formations as might be needed by the army and the navy.19 A further argument against the Air Staff’s claim was that they had shown no eagerness to assume the burden in 1918, when the

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Air Ministry came into being; but it lacked conviction, since circumstances may legitimately alter cases. When all was said, the fact that the Air Ministry had no responsibility for air defence, except the duty of providing squadrons for the purpose when they were demanded, remained an anomaly which at least deserved investigation.

In the course of the enquiry thus set in train, Mr. Balfour was much struck by the disparity between the country’s air resources and those of the only foreign power within striking distance. France was understood to possess a mobile striking force of about three hundred bombers and three hundred fighters, apart from army support squadrons and a Colonial air force of some weight. The nearest equivalent in Great Britain amounted to fewer than forty aircraft. Admittedly the obvious function of the French air striking force was to prevent a violation by Germany of the Treaty of Versailles, and its use against the United Kingdom was exceedingly unlikely. But Balfour argued that even the bare possibility of attack by such a weapon was perilous. So huge a disparity between the striking forces of the two countries seemed to him bound to weaken British diplomacy, inasmuch as it enforced dependence on the goodwill of a neighbour. He asked his colleagues whether they were content to accept that situation, or alternatively were willing to provide a metropolitan air force strong enough to change it.20

On close examination Balfour’s arguments appear by no means overwhelming. His contention that ‘a continuous torrent of high explosives at the rate of 75 tons a day for an indefinite period’ would paralyse the War Office and the Admiralty and render London uninhabitable, either in fact or in the popular estimation, was not supported by much evidence available then or now, though the effects of such an onslaught on a city unprovided with active or passive defences would doubtless have been serious. Moreover his implied assumption that the only answer to attack by a foreign air force was the provision of a rival air force in this country, while it accurately reflected Trenchard’s views, was open to some doubt. It could be argued—and was argued by the Admiralty—that, if the hypothetical enemy did indeed take so improbable a course, prompt naval action against her ports might well persuade her to call off the venture long before an ‘indefinite period’ of bombing had produced the effects foreseen by Balfour.21

There were, however, other arguments for air expansion which may have influenced the Government quite as much as Balfour’s warning. At home a section of the public which believed, with the Prime Minister and General Smuts, that the bomber might become the master-weapon of the future strongly supported the Air Staff’s claim to substantial recognition; abroad, adherents of the ‘strategic’ doctrine of air power might interpret failure to give practical

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expression to it as a sign of weakness on the part of a country hitherto regarded as its chief exponent. Finally the future of British commercial aviation, like that of its military counterpart, was clearly bound up with nourishing aircraft factories. Even on purely economic and financial grounds there was much to be said for nourishing a branch of industry which would certainly languish without orders from the air force.

In the light of such considerations the Government decided, in the spring of 1922, to meet the Air Ministry’s desire for the leading role in air defence, and a few months later accepted a scheme for the provision of a metropolitan air force of fourteen bomber and nine fighter squadrons.22 The proportion of bombers to fighters reflected the Air Staff’s faith in the axiom that offence was the best means of defence.

The transfer of responsibility for the air defences from the War Office to the Air Ministry was left to the two departments to arrange as best they might.

Outwardly, the simplest method would have been for the former to hand over to the latter all the air defence formations hitherto at its disposal; but in practice that course would have led to many difficulties. The army’s anti-aircraft artillery and searchlight units were the nucleus of a formation intended to guard an Expeditionary Force during mobilisation and in the field; hence their loss would have deprived the service of resources needed for a purpose clearly distinct from home defence. Again, the officers and men concerned could not have been transferred en bloc to a new master without some hardship and much administrative complication; at the same time the air force was not itself in a position to man the formations, and had little experience of anti-aircraft gunnery. Finally, a transaction on that scale would have saddled the Air Ministry with burdens from which it might well shrink, especially as the Air Staff held that excessive preoccupation with purely defensive measures was to be avoided as inimical to development of the offensive arm which they regarded as the best means of deterring an aggressor or defeating him.

The outcome was an arrangement which substituted one set of problems for another. The departments agreed to adhere to methods previously contemplated, insofar as the War Office would continue to provide and man such guns and searchlights as might be necessary for air defence at home, and the Air Ministry to provide and man the fighter squadrons needed to complete the purely defensive component of the system. In addition the Air Ministry would furnish an offensive component in the shape of a substantial bomber force. As the Air Ministry were now to be the masters, the War Office would consult them about the ‘primary disposition’ of the guns and searchlights, and the principles governing their employment. Operational control of the whole complex would be exercised by an air officer.23

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Although perhaps the best that could be made, this bargain was in all respects a satisfactory one for either party. On the one hand, Air Ministry assumed a welcome yet onerous responsibility for functioning of the system, without gaining effective control over technical development of that part which was manned by soldiers; on the other, the War Office lost the power of deciding when guns should fire or searchlights be brought into action, but not the burden of providing, manning and financing them. To promote co-operation in matters of research, development, ‘primary disposition’ and tactical employment, an existing sub-committee of the Committee of Imperial Defence, hitherto concerned only with home ports, was renamed the Home Defence Committee and given power to consider questions of air defence. In practice, neither the War nor the Air Ministry found much occasion during the next few years to remit such problems to that body. During that time those which called for joint consideration were either discussed informally entrusted to small committees set up as the need arose.

The Government’s decision to adopt the plan for a metropolitan force found the War Office and the Air Ministry in the thick of negotiations connected with the transfer of responsibility. A joint-service committee had recently been established under Air Chief Marshal Trenchard to discuss the creation of a bomber force and the organisation of a defensive zone. Its first step was to instruct a sub-committee to consider the second point.24 The sub-committee, headed by Air Commodore J. M. Steel of the Air Ministry and with Colonel W. H. Bartholomew of the War Office as leading representative of the War Office, went on the assumption that the nine fighter squadrons recently sanctioned by the Government would be available by 1925. Their plan, to which we shall revert, may be regarded as the direct, though somewhat remote, forebear of the system which enabled the country to survive the German onslaught in 1940.


The twenty-three squadron scheme of air expansion was accepted and announced by the Coalition Government in August, 1922. Its obvious weakness was that it fell short of the situation it was outwardly designed to meet. Ostensibly at least, its purpose was to protect the country against a possible attack by some three hundred bombers supported by the same number of fighters. Yet it made provision for only nine regular and five auxiliary bomber squadrons with a total establishment of 158 aircraft. If Balfour’s warning provided any real basis for the existence of the force, that number was manifestly inadequate. According to the sponsors of the scheme, the

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strength could be swelled in an emergency by reserves and training units; but any emergency which justified so desperate an expedient would have to be both very grave and of very brief duration.

That the scheme would be open to such criticisms did not escape the Government when they adopted it; but on several grounds they were reluctant to aim higher. One good reason was that the Air Ministry believed that rapid expansion would be difficult, and had indeed begun by putting forward a still more modest programme. On that ground alone, ministers may well have felt that small beginnings were preferable to an ambitious project for which recruits and political support might not be forthcoming. Perhaps an even stronger argument was that, as the danger of attack by France was merely hypothetical, the size of the French air striking force was not a true criterion of this country’s needs; but to put the matter thus might have invited the rejoinder that, if that were so, the case for a metropolitan air force had not been made out. In the light of subsequent events we may perhaps conclude that at any rate the number of squadrons proposed was not too great, especially as henceforward the metropolitan air force formed the main reserve for air formations overseas.

Within the next few months new factors threw fresh doubt on the adequacy of the proposals. Towards the end of 1922 the Coalition Government was replaced by a Conservative Government led first by Mr. Bonar Law and later by Mr. Stanley Baldwin. Thus the scheme came under the eyes of an administration keenly critical of much that had been done or left undone in the field of national and Imperial defence. Soon afterwards Franco-British relations were temporarily overclouded by differences of outlook on the reparations problem; and after French troops had occupied the Ruhr, a serious dispute with our Continental neighbour, though still unlikely, may well have struck observers as rather less so than it had seemed six months before.

Soon after taking office the new administration appointed a committee under Lord Salisbury ‘to enquire into the co-operation and correlation between the Navy, Army and Air Force from the point of view of National and Imperial Defence generally’. The Government had in mind such questions as the advantages and disadvantages of a suggested Ministry of Defence, and the possibility of improving on existing arrangements for the provision and employment of air squadrons working with the fleet. But they asked the committee to deal also with ‘the standard to be aimed at for defining the strength of the Air Force for purposes of Home and Imperial Defence.25 After hearing evidence from Air Chief Marshal Trenchard, who stressed the potentialities of the bomber and mentioned indications that the French were planning a big expansion of their air force, Lord Salisbury

Map 1

Map 1. The Steel-Bartholomew Plan, February 1923

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and his colleagues came to the conclusion that the existing disparity between British and French air power created a ‘menacing’ position calling for prompt action.

The sequel was the adoption by the Cabinet, on 20th June 1923, of a new scheme of air expansion designed to provide in the first instance a metropolitan air force of fifty-two squadrons with a first-line establishment of 394 bombers and 204 fighters.26 The Government contemplated the attainment and maintenance of approximate numerical equality with the French air striking force, but expressed the hope that international agreement on the lines of the Treaty of Washington might help them or their successors to achieve it without cutthroat competition. While British and French diplomacy were out of step there was, however, little prospect of striking such a bargain.

The Air Ministry were thus faced with the creation of a force considerably larger than that hitherto envisaged. And while such an extension of their kingdom was doubtless welcome—the figure of roughly 600 machines as a first step was indeed that specified by Trenchard—its attainment was not likely to be easy. Early in November the Secretary of State for Air, Sir Samuel Hoare, reported that, notwithstanding the Government’s avowed intention of achieving air parity with France as rapidly as possible, the earliest date by which the fifty-two squadrons could be ready was the end of 1926.27 By that time, if the Air Staff’s fears were realised, the French air force would also have expanded, so that parity would still be lacking. Moreover the Government could feel no certainty that such popular support for air rearmament as was forthcoming in 1923 would sustain them or their successors in the future. Nevertheless the programme made such a good start that by the autumn of 1925 twenty-five of the fifty-two squadrons were in being.

Meanwhile the Steel-Bartholomew Committee had drawn up its defence plan.28 Although framed with the short-lived twenty-three squadron scheme in view, it deserves attention on its merits and as the ancestor of distinguished progeny. (See Map 1) Its most important feature was an ‘aircraft fighting zone’ some fifteen miles deep and stretching round London from Duxford in Cambridgeshire to Salisbury Plain. The zone would be set well back from the coast in order that defending fighters might have time to reach the appropriate height while hostile aircraft were approaching. Warning of approaching raids would be given by distant sound-locators on the coast, and by a belt of advanced observer posts near the perimeter of the zone. The committee recommended that guns should be deployed both in an ‘inner artillery zone’ for the close defence of London, and also in an ‘outer artillery zone’ sandwiched between the aircraft fighting zone and the observer belt. Searchlights would be deployed in the inner artillery and aircraft fighting zones, but not in the outer

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artillery zone, whose guns would fire only by day, and for the purpose of breaking up hostile formations and guiding fighters towards the enemy, rather than of engaging individual aircraft. Other ‘inner’ artillery zones would provide similarly for the close defence of major ports. Dependence on sound-locators and human observers was a limitation obvious enough to-day, but less apparent, and indeed less serious, at a time when aircraft flew comparatively slowly.

The Steel-Bartholomew Committee estimated that, besides the nine fighter squadrons contemplated in the twenty-three squadron scheme, eleven anti-aircraft brigades (later called regiments) and seven searchlight battalions, with an aggregate establishment of 264 guns and 672 lights, would be needed to make their plan effective. Six of the artillery brigades and three searchlight battalions less two companies would be forthcoming under arrangements already contemplated by the War Office, who had begun to form two Territorial air defence brigades and were willing to make the 1st Air Defence Brigade available for home defence meanwhile.* But while there was no lack of guns in store, the bringing of these units up to strength, to say nothing of the raising of the others needed to complete the plan, was bound to be a long-drawn business.

Important progress was made in 1924, when a committee headed by Major-General C. F. Romer went to work on the basis of a revised plan which reflected the new and larger scheme of air expansion. Among the members was Major-General E. B. Ashmore, whose command of the air defences guarding London and the south of England during the later stages of the recent war had been followed by command of the 1st Air Defence Brigade. General Ashmore could be reckoned the country’s leading authority on air defence and had viewed with much misgiving the disbandment of the air defences after the Armistice. The tasks expressly assigned to the committee were concerned mainly with the devising of a suitable system of command, of measures needed to give warning of approaching raids, and (with the assistance of an expert sub-committee) of communications commensurate with the extent of the defences now envisaged. But their report was of wider significance, since it embodied much that had been added after the laying of the foundations of the post-war system of air defence by the Steel-Bartholomew Committee. The plan as it now stood made provision for three bomber groups located in Oxfordshire or Gloucestershire, in East Anglia, and in the neighbourhood of Salisbury Plain, and for ten fighter sectors. (See Map 2.) Of the seventeen fighter squadrons comprised in the fifty-two squadron scheme, fourteen would be divided between the sectors; the remaining three would work from forward bases near the coast. A new

* The air defence brigades included both anti-aircraft ‘brigades’ and searchlight units.

Map 2

Map 2. The Fifty-Two Squadron Scheme

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command called Air Defence of Great Britain would direct the operations of bombers, fighters, guns and searchlights, but would delegate immediate control of all but the bomber force to a subordinate command called Fighting Area. Executive orders to gunners and searchlight crews, however, would necessarily pass through army channels. The needs of the inner and outer artillery zones were assessed, as before, at 192 guns in eight brigades or regiments; but defended ports, to which the Steel-Bartholomew Committee had proposed to allot 72 guns and 168 lights, were no longer expressly included in the plan.29

Among the consequences of the Romer Committee’s report were the commencement of recruiting for a new Observer Corps, whose members would undertake the important task of reporting the movements of aircraft across those parts of the country which lay open to attack; and establishment of the new commands which the committee recommended. At the beginning of 1925 Air Marshal Sir John Salmond took up the post of Air Officer Commanding-in-Chief, Air Defence of Great Britain. Clearly the post would be a difficult one, for much that lay before him and his successors was uncharted country. The problems of air defence had changed considerably since the Armistice and were bound to change still more in the future. Moreover the instrument devised for their solution was both untried and inherently imperfect. The dual chain of command through air and army channels, which followed inevitably from the bargain struck in 1922, gave rise in practice to difficulties which only the personal qualities of those called upon to make the system work could overcome. Excessive delegation of authority to Fighting Area, on the other hand, was a weakness not difficult to remedy. Apart from all this, clearly many years of hard work would be necessary to complete the intricate network of communications needed for control in war, extend the observation system over the whole of the area threatened with air attack, and raise the Territorial units ultimately required to man the guns and searchlights. And a point which should have been obvious to all, but may not always have been grasped, was that until those things had been done, the progress of the fifty-two squadron scheme would remain a most misleading index of the country’s ability to resist attack.

In the outcome progress in some of these fields was very slow. We have seen that by the autumn of 1925 nearly half the squadrons envisaged in the scheme of air expansion were in existence; but in other respects the air defences were still in their infancy when that stage was reached. The best part of another year was needed to extend the observation system round the coast from Suffolk to Hampshire.30 Recruiting for the two Territorial air defence brigades whose formation was announced in 1922 had made some progress, but both

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brigades were still much below establishment. And for many years to come such Territorial units as did exist were seldom able to take part in the annual air defence exercises, for their brief periods in camp were necessarily devoted largely to general military training and to gunnery exercises which could not be fitted into the Air Ministry’s arrangements.31

Meanwhile, relations between France and Great Britain had improved and the threatened expansion of the French air force seemed to have been shelved. The prospect of an accommodation between France and Germany threw an unwonted gleam of sunshine on the European scene, presaging conditions which might favour a general scaling-down of armaments and a consequent lightening of taxation. In these circumstances a committee under Lord Birkenhead met’ to consider whether the fifty-two squadron scheme of air expansion could be modified or suspended in the interests of goodwill and economy. In November 1925, the Birkenhead Committee came to the conclusion that the scheme ought not to be abandoned, but that its completion could safely be put back for some years.32 Accordingly a new Conservative administration, in office after a brief period of Labour rule, responded to the news that the scheme could not in any case be completed before 1930 by deciding that completion in 1936 would do.33 Four years later Mr. Ramsay MacDonald’s second Labour Government, faced with an apparently still more urgent demand for economy, postponed completion until 1938.34 A third postponement resulted from the ‘armament truce’ observed in Britain while the Disarmament Conference was sitting at Geneva between 1932 and 1934.

Whatever their political merits, from the standpoint of those who ultimately bore the burden of air defence in the war with Germany these delays were highly inconvenient. In 1923 the Air Staff, notwithstanding their advocacy of air parity with France, had viewed the substitution of the fifty-two for the twenty-three squadron scheme with some misgivings, not because they thought the smaller scheme the better but because they feared the effect of disrupting plans already set in train. Having waived that objection, accepted the larger scheme and thereby agreed to direct their steps towards a more distant goal, they may have felt that they had earned the right to complete at least the first stage of their journey without interruption. In practice they were not allowed to do so. Some years later a spokesman of the Air Ministry expressed the view that the root-cause of the difficulty experienced after 1934 in matching German air expansion lay in the postponements begun in 1925. However that may be, the student may well wonder whether the Birkenhead Committee fully grasped how far the country really was from security, despite the apparent progress made since 1923. Certainly their recommendation caused much dislocation of plans already laid, and not easily recast to suit

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requirements which changed twice more in the next few years. On the other hand it has been argued that on balance postponement did less harm than good, inasmuch as limitations of quantity tended to direct the minds of airmen to quality, thus focusing attention on researches which culminated in far-reaching technical improvements. But the argument is unconvincing. If the fifty-two squadron scheme had been completed in 1930, the state of the air defences would still have left no doubt that only unremitting attention to quality could make them strong.

As it was, the immediate effect of the decision of 1925 was that in the next three years only six squadrons were added to the home defence force. On the date laid down in 1923 for completion of the scheme, the strength of the force stood therefore at thirty-one squadrons instead of fifty-two. No new squadrons were formed in the financial year 1928–1929, but in 1929–1930 six squadrons were added, in 1930–1931 another two, and in 1931–1932 three more. Thus in the spring of 1932 the force was ten squadrons short of its full complement. Meanwhile nearly nine years had passed since the announcement that the whole force was to be formed as rapidly as possible.

One benefit which might be expected to have followed the diminished rate of progress was a better balance between air and ground components. But in fact the gap grew wider. The public had lost the taste for soldiering, the War Office had little money for any but the most urgent measures, and anti-aircraft experts, aware that since the Armistice the technical progress of aircraft had outstripped that of the defences, were in no position to attract recruits by lavish displays or promises of high achievement. Reluctance on the part of the authorities to endorse large measures of expansion until fresh researches had restored the balance would therefore have been understandable even if funds had been available to pay for them. Meanwhile the few who needed no inducement to volunteer were ill supported by their fellows, and the air defence formations sponsored by the army made only modest headway. By 1928, when three-fifths of the air expansion squadrons were in being, all the artillery and searchlight units needed for the inner artillery zone enjoyed a shadowy existence, but were able to man less than half their establishment of guns and lights. Elsewhere the situation was still worse. In the outer artillery zone only one battery towards the twelve recommended by the Romer Committee had been formed; eleven of the twenty searchlight companies needed for the aircraft fighting zone were in existence, but their average strength was about one half of their establishment and they had eight lights apiece instead of twenty-four. By concentrating all available troops and lights the authorities could have manned two sectors out of ten. The Observer Corps, appealing to a section of the public whose inconspicuous achievements deserve

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high praise, had made some progress, but still numbered only four groups centred on Colchester, Maidstone, Horsham and Winchester. Another fourteen groups were needed to complete the scheme.

In the next four years a number of changes were made in the light of experience gained since 1923. At the beginning of 1929 certain responsibilities in regard to the Observer Corps were transferred from the War Office to the Air Ministry, mainly on the ground that the air force were the chief users of the information furnished by the Corps, and were better able to stimulate recruiting.35 A retired air force officer (Air Commodore E. A. D. Masterman) was appointed Commandant; and the Air Officer Commanding-in-Chief, Air Defence of Great Britain, became responsible for training and was authorised to call out the Corps if the need arose. The Corps remained a civilian body, raised and paid or reimbursed through the agency of the Chief Constables in the areas concerned; the members were sworn in as special constables and were required to signify their willingness to be called out if they were needed. As a result of close reasoning from practical trials the decision to exclude searchlights from the outer artillery zone was rescinded; and in due course the guns and lights of the Thames and Medway area—originally an outlying artillery zone like the other defended ports—were incorporated in the scheme. Both changes were steps towards the later ideal of a unified air defence scheme covering all threatened areas. But their immediate effect was to increase still further the disparity between the number of lights approved and the number that could be found and manned.

The outcome of nine years’ work was, therefore, that when in 1932 a grave warning from the professional heads of the fighting services, coupled with a manifest decline in international relations, forced the Government to abandon the assumption that there would be no major war for a decade, four-fifths of the air expansion scheme had been completed, but the Territorial formations needed to man guns and searchlights had less than seven-tenths of their peace establishment and only about one-third of the numbers they would need in war. There were still only eleven searchlight companies towards the twenty needed in the aircraft fighting zone, the four artillery brigades assigned to the outer artillery zone continued to be represented by a single battery, and there were no searchlights in that zone, although their provision had been sanctioned two years earlier. Few opportunities had been found for realistic training by all arms together, communications were incomplete and the warning system was notoriously inadequate. Had war come soon, many parts of the air defence system would have been lacking and no part could have functioned with full efficiency.36 But as the outbreak of hostilities was in fact postponed for seven years, the deficiencies of 1932 are perhaps of less importance than the use made of the respite.