The RAF's victory over the Luftwaffe during the Battle of Britain in the summer of 1940 made a German invasion of Britain all but impossible. In his book Bomber Offensive, published in 1947, Marshal of the Royal Air Force Sir Arthur Harris wrote that all the credit for preventing the invasion of Britain had been given to Fighter Command. He felt that the influence and importance of Bomber Command's role in the Battle of Britain had been largely overlooked. Germany's failure to defeat the RAF and secure control of the skies over southern England convinced Hitler to indefinitely postpone the planned invasion of Britain. While this victory was decisively gained by Britain's fighter defences, other organisations also contributed.

Conflicting demands on Bomber Command

During the Battle of Britain, Bomber Command suffered from fundamental disagreements within the military and political leadership about how it was best employed, as well as from multiple and often conflicting demands upon its relatively limited resources. In the years before the Second World War, the development of the RAF was dominated by the belief that the service would be best employed in a strategic air offensive against Germany. A series of 'Western Air Plans' was formulated, listing strategic targets for attack. The offensive began on 15 May 1940, five days after the German invasion of France and the Low Countries, and would last until virtually the end of the war. It was, for some years, the only means of taking the war directly to Germany itself. However, with the prospect of air attack and invasion, Bomber Command was beset by conflicting demands upon its resources.

At first, Bomber Command's main objective was the reduction of the threat from the German air force against Britain. Whitley, Wellington and Hampden heavy bombers were to attack German aircraft factories and assembly plants by night and Blenheim medium bombers would raid aerodromes in occupied territory by day. When, from late August onwards, German shipping began to concentrate in preparation for an invasion of Britain, ports from northern Germany to the French Channel coast became the primary targets. However, in directives issued by the Air Ministry throughout the summer, due regard was still paid to the strategic offensive. Attacks were ordered on the oil industry, communications, forests and crops. Minelaying in German coastal waters was also to be undertaken. These objectives enjoyed varying priority at different times.

Such a multiplicity of targets ensured that concentration of effort could not be brought to bear against any one in particular. Moreover, poor navigation and bombing techniques as well as a lack of knowledge and an over-optimistic view of the results of bombing made Bomber Command's early operations mostly very ineffective. Night-time raids on inland targets were impossible without bright moonlight, and even then these targets were difficult to find. Raids against invasion ports, because of their proximity to Britain and easily found positions, were much more successful.

Responding to the fall of France

At the beginning of May, before the German invasion of France and the Low Countries, the Chiefs of Staff (COS) Committee reviewed the strategic situation on the assumption that Germany would seek a decision in 1940. Of the two possible ways of achieving this - major attacks on either Britain or France - the Chiefs of Staff thought attacks on Britain more likely. The main threat to the United Kingdom's security would thus come from an intensive German air offensive. Although it was expected that serious material damage and dislocation would be caused to Britain's air force and aircraft industry, it was thought that the Luftwaffe would not succeed in its vital aim of neutralising the RAF's air striking force. It was essential, the COS concluded, that all possible measures should be taken to expedite the production of anti-aircraft equipment and bomber and fighter aircraft, even at the expense of the country's long-term armament programme.

A mere three weeks later, in light of the German invasion of France and the Low Countries, the COS had to re-examine British strategy in case of the complete collapse of French resistance. It was clear that Britain would be subjected to the concentrated attack of German air and naval forces operating at the shortest possible range from Norway to France. Undoubtedly, the key role in the successful repulsion of this grave threat would be played by British fighter squadrons. But, as the COS wrote in a report on 25 May, 'we cannot resist invasion by fighter aircraft alone. An air striking force is necessary not only to meet the sea-borne expedition, but also to bring direct pressure to bear upon Germany by attacking objectives in that country'.

On 20 June, a few days after the fall of France, Bomber Command's Commander-in-Chief Air Marshal Charles Portal was directed by the Air Ministry to launch his striking force primarily against objectives that would result in the immediate reduction of the scale of German air attacks against Britain. The directive listed airframe assembly factories, aluminium plants and equipment depots within range in Germany as the most urgent targets, though some members of the Air Staff had reservations about the first of these. It was felt that the destruction of assembly factories would not appreciably reduce the effort of the Luftwaffe because the level of its reserves would ensure attacks could be maintained at full intensity during the period in which the factories were re-established out of range. However, attacks on the main equipment and maintenance depots would have an immediate effect as these units were organised to provide major maintenance facilities for front line squadrons and the fitting out and supply of reserve aircraft to replace wreckage.

It was thought that German communications were fully stretched in distributing supplies to forward areas. The directive to Portal therefore ordered him to assault railways and canals. The principal focus of attack should be the marshalling yards of the Ruhr and Cologne areas, in particular the main yard at Hamm, and the aqueducts carrying the Dortmund-Ems canal over the River Ems near Munster. One squadron was also to continue laying mines in German coastal waters. Subject to these primary tasks, operations were to continue against oil targets, especially all major stocks in the newly-occupied territories before they could be utilised by enemy forces. Preparations were also to be made to set alight German crops and forests using a new incendiary pellet that would be ready in early July. Bomber Command's medium bomber squadrons were to attack enemy occupied airfields in northern France and the Low Countries in order to destroy as many aircraft as possible and force the rest to withdraw to locations in the rear. Finally, Portal was directed that he should be prepared at short notice to divert all his bombers against an invading enemy naval force.

Fears of invasion were increasing rapidly. Prime Minister Winston Churchilltold the Cabinet on 3 July that there was a growing feeling that an attempt might be imminent. He appreciated the reasons put forward by the Chief of the Air Staff (CAS), Air Chief Marshal Sir Cyril Newall, for the RAF's present concentration on the German aircraft industry, but considered that the coming week might be so critical that it justified transferring priority to the bombing of enemy harbours and shipping.


Hampdens of No. 14 Operational Training Unit

A gunner's view of a formation of Hampdens of No. 14 Operational Training Unit (OTU), based at Cottesmore in West Sussex, 23 July 1940.

The following day, Portal was directed to make these targets his first concern, with particular emphasis on Kiel, where the capital ships Scharnhorst and Deutschland were berthed, as well as Hamburg, Bremen, Rotterdam, Wilhelmshaven and Brunsbuttel. The minelaying deployment was increased to three squadrons and the offensive against the aircraft industry and oil was to be maintained. Though initially dropped, after discussion between Portal and Deputy CAS Air Vice-Marshal Sir William Sholto Douglas it was agreed that the effort against communications should continue in a limited way.

For the Blenheims of 2 Group, the priorities would now be: the attacking of barges and small craft on the canals and in the ports of Holland and Belgium, the continued daytime disturbance of targets attacked in Germany by night, and raids against concentrations of aircraft at aerodromes in north-west France and Belgium and shipping reported in Norwegian ports. Because of the high vulnerability of aircraft engaged in day bombing, attacks were to be made sporadically and only when adequate security through sufficient cloud cover was available. 2 Group was to employ up to 48 aircraft per day, operating individually or in small groups. Every effort was to be made to spread attacks so that the resulting calls for German fighter protection would be widespread and numerous, keeping the fighter defences dispersed.

The threat of immediate invasion receded somewhat when it became apparent that Germany was concentrating increasingly on preliminary air attacks against Britain. The Air Staff considered that operations up to this point had been too dispersed and issued a corrective order on 13 July, which went to the heart of the problem of Bomber Command's operational effectiveness. The Air Staff now requested that fewer targets be attacked more vigorously with the aim of complete destruction, not harassment. Only five airframe assembly factories, five equipment depots and five oil plants were selected as primary targets.


Blenheim crews of No. 110 Squadron

Blenheim crews of No. 110 Squadron at Wattisham add Le Bourget to a list of recent targets, August 1940.

When he received the directive, Air Marshal (now Sir Charles) Portal was provoked into a detailed and lengthy criticism of the difficulties of applying it. Very few of the objectives would be found by average crews, while even expert crews would require the help of clear nights with a full moon to succeed. Most of the targets were isolated and in sparsely inhabited areas far to the east in Germany. Therefore, he expected a high percentage of wasted effort in searching for and reaching them, while those bombs which were badly aimed would hit nothing else of importance.

Portal believed the most effective way to realise Bomber Command's aim of reducing the scale of air attack on Britain was to cause dislocation to the largest possible number of factories by periodic assaults rather than attempting to obliterate a select few. This was partially because the obliterated target exercised no moral effect once the factory workers had been removed and it could always be rebuilt in a safer area. He responded to the charge that the effort of his Command had been too greatly dispersed by explaining that tactical factors, such as the weather and limited amounts of darkness, often made it unavoidable. However, he also saw virtue in this as the scatter attacks spread alarm and disturbance over a wide area. Portal also pointed out that the designation of communications as 'last resort' targets was unrealistic. The value of such targets depended almost entirely on their geographical location and visibility, and therefore they should always be between the primary objective and the home base.

The day following his letter to the Air Ministry, Portal wrote another to Douglas, which he described as 'entirely personal' in order to express the views he could not say in his official capacity. He felt that the selection of such a narrow aim as the reduction of the scale of air attack on Britain by the Air Staff was a 'tremendous mistake' and questioned whether attacks on aircraft factories had any effect on limiting the German air effort at all. Portal wanted a much more positive role for Bomber Command, which he saw as 'the one directly offensive weapon in the whole of our armoury'. Therefore he suggested to Douglas that the RAF should take as its aim the greatest possible disruption of German war industry with the greatest possible moral effect.

Douglas, in summarising Portal's letter to the CAS on 20 July, suggested that a meeting be held with the C-in-C. In an agenda for this forthcoming conference, the Air Staff made clear their unease with Portal's position. His desire to attack wide ranging targets periodically, in preference to obliterating a select few, appeared in direct conflict with the principle of concentration, upon which their offensive plans were based.

It was the Air Staff's belief that moral effect, despite being an extremely important subsidiary result of bombing, could not be decisive - material destruction had to be the primary object. Moreover, it was crucially important to continue the offensive against Germany's aircraft industry. The Air Staff appreciated the tactical and operational constraints of Bomber Command and conceded that too restricted a list of objectives might have been given. But they also hoped to avoid the wide dispersion of former directives to give Portal a limited number of targets on which to concentrate his force during the current phase of operations.

The conference between Portal and the Air Staff made little difference to Bomber Command's objectives which, in a new directive issued on 24 July, remained the reduction of the scale of air attack on Britain. However, in deference to Portal, the number of primary targets was increased and the offensive against oil was raised again to second priority. Portal's opposition to the Air Staff's defensive bombing policy and its failure to unleash the full potential of the strategic air offensive did not bear fruit until the autumn, after the Battle of Britain was over and not until he himself became Chief of the Air Staff. Portal's mind was soon changed abruptly, but briefly, as the German air assault began to intensify in early August.

Churchill was alive to the political and propaganda possibilities of the course of the Battle of Britain. He asked Secretary of State for Air Sir Archibald Sinclair whether, in case of a German raid on London, the RAF had the capability to reply immediately against Berlin. Sinclair replied on 23 July that the Hampden, Wellington and Whitley heavy bombers, and the Blenheims with a light load, could all reach the German capital. A limited capability was available at once, but from 2 August the whole of the heavy bomber force could be employed. With 12 hours' notice, 65 to 70 tons could be dropped and repeated every night for a week. With 24 hours' notice the bomb lift could be increased from 130 to 150 tons, repeated every alternative night for a week. If a heavy single blow was desired, the bomb-load could rise to 200 tons.

At the end of July, however, anti-invasion preparations were of the greater moment. Both the COS Committee and the Air Staff agreed that to attempt and sustain an invasion, Germany would have to gain air supremacy over the areas where it would require secure sea communications between the continent and the British coast. Therefore, while Bomber Command would continue to reduce the scale of German air attack by striking at suitable objectives in Germany, it would also be prepared to divert its efforts to the attack of enemy shipping concentrations, especially troop-carrying vessels, should these materialise. If a seaborne invasion was launched, Bomber Command would attack transports at sea and at landing points.


A Hampden Mk 1 of 49 Squadron being 'bombed up'

A Hampden Mk 1 of 49 Squadron being 'bombed up' at Scampton, June 1940. On 12-13 August, aircraft of 49 and 83 Squadrons successfully blocked the Dortmund-Ems Canal, which halted the flow of invasion barges from the Rhineland to the coast for 10 days. For his part in the operation, Flight Lieutenant R A B Learoyd of 49 Squadron was awarded the Victoria Cross.


During August, as the Battle of Britain became more fiercely joined, Bomber Command's effort against the German air force increased accordingly. Of the 2,227 sorties it flew in the month, 714 were against aerodromes in occupied Europe, almost twice as many as in July, and 435 against the German aircraft industry. Until 12 August, the Blenheim squadrons of 2 Group attempted day operations but, due to heavy losses, had to revert to night raids. On 17 August, the Air Ministry called on Bomber Command for increased attacks against those aerodromes in occupied Europe from which the enemy's air assault was being launched.

Owing to the paucity of reconnaissance reports, it proved very difficult to assess the results of these attacks. Moreover, doubts had always been held by some members of the Air Staff about the uneconomical nature of airfields as targets. German attacks were launched from some 400 different aerodromes in northern France, Holland and Belgium and the Luftwaffe operated efficient dispersal and protective schemes. Therefore, Bomber Command never knew before launching raids which of the aerodromes were actually in operation.


Wellington bomber crews

A Wellington bomber and crews of 149 Squadron after their return from Bomber Command's first attack on Berlin on the night of 25-26 August 1940.

The inadvertent bombing of London by German aircraft of 24 August provoked immediate retaliation by Bomber Command against Berlin the following night. More raids in the same week and the general damage caused to German cities by the air offensive were contributory factors in the Luftwaffe's change of air attack priority from Fighter Command's airfields to London on 7 September, the turning point of the Battle of Britain. On 29 August, Churchill told the Cabinet he proposed sending a message of congratulations to Bomber Command on the bombing of Berlin. In view of the indiscriminate bombing by the Germans, it was possible that, in the near future, the Government might have to consider a temporary but marked departure from its policy of bombing only military targets.


Return from the first raid on Berlin

Wellington bomber crews photographed at a press event after the first raid on Berlin, which took place on the night of 25-26 August 1940.

At the beginning of September, the Prime Minister suggested to Portal that the bombing offensive should now be spread as widely as possible over those German cities and small towns within Bomber Command's reach. The Vice-Chief of the Air Staff, Air Marshal Sir Richard Peirse, pointed out to Churchill that such a plan had been devised already for use in the winter when unfavourable weather conditions might prevent the precise bombing of targets. However, the Air Staff preferred not to disperse its effort on to other targets, but to continue with the offensive against German aircraft industry, oil and communications objectives. Peirse contrasted what the Air Staff believed to be the effectiveness of the RAF's bombing, which was planned and relentless until a particular objective was considered to have been destroyed or dislocated, with the German effort, which was sporadic and mainly harassing. Moral effect was not gained by harassing, he told Churchill, but was proportionate to the material damage done. The complete destruction of a target was therefore the best way to cripple Germany.


A briefing with the station commander

Wellington crews study maps at a briefing with the station commander on 2 September 1940. 

Political pressure for retaliation against German indiscriminate bombing continued. On 10 September, the Cabinet agreed that Bomber Command's aircraft should be instructed not to return home with their bombs if they failed to find their primary targets. However, two days later Churchill allowed an earlier Air Ministry signal, issued before the Cabinet meeting, to stand. It instructed Bomber Command that it was not the intention to bomb at random nor that pilots should never bring back their bombs. But it also made clear that every attempt was to be made to bomb alternative or last resort targets


Airmen working on a Wellington bomber

RAF ground crew working on a Wellington bomber, 9 September 1940.

On 19 September, Churchill told the COS Committee that the dropping of large parachute mines by the Luftwaffe proved the Germans' intention to perpetrate an 'act of terror' against the British civil population. He wanted preparations made for equal retaliation to be inflicted on ordinary German cities. The Cabinet agreed that aerial mines should be dropped on Berlin and on 21 September the COS replied that they were in favour of giving the German population 'a taste of their own medicine'.


Dunkirk harbour after attacks by RAF bombers

A reconnaissance photograph of Dunkirk harbour after attacks by RAF bombers, 19 September 1940. Substantial damage has been caused to dock installations and some of the invasion craft. After the war, Arthur Harris wrote that it had become customary to allow aircrews in the final stages of training to undertake the routine bombing of coastline targets, which could be identified and hit with little difficulty. 


These demands were initially resisted by the Air Staff. They pointed out that, because Bomber Command was considered capable of precision attacks, indiscriminate bombing was unnecessary and futile. Moreover, it would be unwise to start competitive bombing when the Luftwaffe's striking force was four times larger than the RAF's and, to reach Berlin, British aircraft had five times as far to travel as German aircraft had to reach London. However, as a reply to the bombing of London, a raid of the largest possible scale on Berlin was ordered and carried out by 119 aircraft on 23-24 September.

The Air Staff directive of 21 September instructed Bomber Command that, although there were no objectives in the area of strategic importance, periodic attacks on Berlin were to continue in order 'to cause the greatest possible disturbance and dislocation' to industry and the civil population. The quickest, most lasting and effective means of achieving this would be by attacks on sources of power. Nevertheless, the directive reiterated the Air Staff's view that in accordance with long-term offensive strategy, focus should remain on destroying German oil resources and communications. Bomber Command was requested to continue to deploy a proportion of its effort against these objectives, despite the intensive operations being taken against German invasion preparations.

The Air Staff's line of thinking was not met with complete agreement by Bomber Command. Churchill's suggestions were received with greater sympathy by Portal, who returned to the ideas he had advocated in July. On 11 September he told the Air Ministry that each indiscriminate Luftwaffe attack on a British town should be answered in kind by the RAF. A Bomber Command memorandum of 30 September expressed the view that the strategic offensive should now be directed at 'the will of the German people'.

These developments in policy had implications for the long-term execution of the strategic air offensive throughout the rest of the war and are therefore of high significance. However, the role for which Bomber Command was of greatest value during the summer of 1940 was its contribution to the prevention of a German invasion of Britain. In September, the threat of invasion grew to such proportions that sixty per cent of Bomber Command's effort was deployed against invasion targets. In the first days of the month, extensive movements of shipping began from north German ports to embarkation harbours in Belgium and France. On 5 September, the RAF made its first major raids against these concentrations. Two days later, with the issue of an invasion alert, the Air Ministry signalled to Bomber Command that 'all available bomber effort' for the night's operations was to be directed against invasion shipping. Hourly reconnaissance between 10.00pm and 4.00am the following morning were required to identify any movement of barges or shipping in or out of the harbours at Ostend, Nieuport, Dunkirk, Calais and Boulogne.

As September progressed, so the level of Bomber Command's attack increased. On the night of 13-14, the whole of the available bomber force was dispatched against the barges. The following night the number of sorties rose to 176 and again to 192 on 17 September. The operations enjoyed greater success than those aimed at Bomber Command's other targets.

The extent of the threat of invasion was outlined in the Joint Planning Staff's (JPS) report of 18 September. The JPS considered that the Germans had 'virtually unlimited' numbers of barges for a short sea crossing, which could transport 150,000 men with their equipment and four days' supplies. Taking into account considerations of wind, tide and the average speed of the barges, it was thought possible for craft from all ports between Ostend and Boulogne to reach the Kent coast moving by night. Despite the immense navigational difficulties and the possibility of sinking many barges during the crossing, the JPS expected large numbers to arrive on British shores.

On 20 September, Air Commodore N H Bottomley, Senior Air Staff Officer at Bomber Command, informed Portal that the JPS indicated that the most vulnerable time for a German seaborne expedition would be during the landing period, when running up to and discharging on the beaches. Bottomley thought the memorandum failed to stress the vulnerability of a barge borne expedition at the ports of concentration. He advocated taking advantage of the prevailing moon conditions and sending Wellington heavy bombers on two sorties a night with maximum loads. Bomber Command's Whitley squadrons could thereby be released to fulfil the Air Ministry's desire to continue the attack on objectives in Germany. Portal replied the next day that he agreed, except that it would be better to work all crews three nights running than twice in one night.

'In the immediate future, while the imminent threat of invasion remains', the Air Ministry Directive of 21 September explained, 'the greater part of the bomber effort must continue to be employed against anti-invasion objectives'. The primary aim of Bomber Command would be the destruction of the major concentrations of shipping at enemy ports, with the secondary object of harassing facilities and communications within and adjoining the ports so as to dislocate the mounting and despatch of the invasion.

Because it was believed that German invasion preparations were complete, and with the current operational emphasis on ports and shipping, the Air Ministry felt that the attacks on the German aircraft industry no longer had any immediate effect on the present situation. As a longer term policy, but one likely to have a more lasting impact on the German air force during the coming winter and early months of 1941, Bomber Command was directed to attack aluminium plants and key component factories.

On 17 September, just as Bomber Command's effort against invasion targets was reaching its height, Hitler postponed the invasion. The subsequent dispersal of German shipping was soon noticed by Coastal Command's photographic reconnaissance aircraft and on 30 September, the Air Ministry signalled Bomber Command that the imminence of invasion had 'somewhat receded'. In such circumstances, particularly when weather conditions were unsuitable for cross-Channel operations, authority was now given to increase efforts against objectives in Germany in compliance with the instructions given in the directive of 21 September

By October 1940, the failure of the Luftwaffe to eliminate Britain's fighter aircraft defences and win control of the skies over the English Channel and southern England ensured that the vital pre-conditions for a successful invasion of Britain had not been met. Fighter Command had won the Battle of Britain. However, the effectiveness of Bomber Command's attacks on the enemy's invasion ports and shipping had made an important contribution to the victory. Although only ten per cent of the assembled barges and other vessels had been destroyed, Bomber Command had caused the Germans great difficulty in gathering an invasion fleet and demonstrated the futility of attempting to launch a seaborne invasion across the Channel.


Handley Page Hampden of No. 83 Squadron

Handley Page Hampden of No. 83 Squadron with crew, seated on a loaded bomb trolley at Scampton, Lincolnshire, 2 October 1940


Bomber Command, fashioned as the instrument of the strategic offensive, had been pre-occupied with the threat of invasion and the reduction of the scale of German air attack throughout the Battle of Britain. Nevertheless, as the Air Ministry had been determined to continue the long term assault on German industry, Bomber Command undertook as many strategic operations as possible. The effect on the German economy in 1940, however, was negligible. The targets selected were too many and various for the small bomber force then available. Navigation and target location techniques were so inadequate that it was not unusual for aircraft to bomb not only the wrong factory but also the wrong city. Most unfortunately, the Air Staff and Bomber Command were completely unaware that their optimistic appraisals of the damage caused to German industry were grossly exaggerated. Not until after the Battle of Britain was over did night photography of bomber operations and photographic reconnaissance begin to become available and not until 1941 was it realised that these types of damage assessment were the only accurate and worthwhile methods.

The growing realisation of these problems led the Air Ministry, particularly after the appointment of Portal as Chief of the Air Staff in October 1940, to move from a policy which placed less emphasis on precision bombing of targets to one which selected objectives that were not isolated but, if possible, grouped within large centres of population or industry.

A longer version of this article, written by Neil Young (former IWM Historian), appeared in the Imperial War Museum Review, No. 6 (1991).

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