Some Problems and Achievements of Anti-Aircraft Gunnery
during the Battle of Britain
(Report by the 6th Anti-Aircraft Division dated 2nd August, 1941; author's interpolations in square brackets)
Abbreviations H.A.A. = Heavy Anti-Aircraft L.A.A. = Light Anti-Aircraft G.O.R. = Gun Operations Room A.A.L.M.G. = Anti-Aircraft Light Machine-Gun V.I.E. = Visual Indicator Equipment G.P.O. = Gun Position Officer G.L. = Radar Set for Gun-Laying V.P. = Vulnerable Point F.A.S. = Forward Area Sight S.O.R. = Sector Operations Room G.D.A. = Gun Defended Area
1. LAYOUT OF A.A. DEFENCES
(a) The area covered by 6th AA. Division coincided with the R.A.F. sectors Debden, North Weald, Hornchurch, Biggin Hill and Kenley (i.e., the major part of No. 11 Fighter Group, R.A.F.). Thus the coastal boundary extended from Lowestoft (exclusive) in the north to Worthing (exclusive) in the south; the internal boundary marching with that of the metropolitan area.
(b) Distribution of A.A. defences was briefly as follows:
The divisional area contained four main 'gun defended areas' at Harwich, Thames and Medway North (guns emplaced along the north bank of the Thames Estuary), Thames and Medway South (guns emplaced along the south bank of the Thames Estuary and defending Chatham and Rochester) and Dover (including Folkestone) . In addition, H.A.A. guns were deployed for the defence of certain aerodromes.
Each 'gun defended area' was based on a Gun Operations Room: at Felixstowe, Vange, Chatham and Dover respectively. This G.O.R. was connected directly to No. 11 Fighter Group Operations Room at Uxbridge, from which it received plots of enemy raids, which in turn were passed down to all gun sites.
The armament of each H.A.A. site consisted of the following: 4 (sometimes 2) 4.5-, 3.7- or 3-inch guns with predictor. Appendix
A [not reproduced] shows the H.A.A. defences as at the beginning of August 1940 and the end of October 1940.
45 Vulnerable Points in the divisional area were defended by L.A.A. guns. These V.P.'s consisted of Air Ministry Experimental stations, fighter aerodromes, dockyards, oil depots, magazines, industrial undertakings and factories.
Armament consisted of the following guns: 40-millimetre Bofors (with Predictor No. 3 and Forward Area Sights), 3-inch 20-cwt. (Case I), AA.L.M.G. and 20-millimetre HispaNo. Appendix B [not reproduced] shows the V.P.'s with their armament as in August and October 1940.
Searchlights were deployed in single-light stations at approximately 6,000-yards spacing throughout the area, but with a closer spacing in certain instances along the coast and in 'gun defended areas', where the distance between lights was approximately 3,500 yds.
These lights were deployed on a brigade basis following R.A.F. sectors, and each light was connected by direct telephone line and/or R.T. [radio-telephony] Set No. 17 to Battery Headquarters via troop HQ,, and thence to an army telephone board at the R.A.F. Sector Operations Rooms.
The equipment of a searchlight site consisted of the following: 90-centimetre projector with, in most cases, Sound Locator Mark III. In some instances sites were equipped with Sound Locators Mark VIII or Mark IX. During the late summer and autumn the number of Mark VIII and Mark IX Sound Locators gradually increased, and V.I.E. equipment and 150-centimetre Projectors were introduced. Each searchlight site was equipped with one AA.L.M.G. for use against low-flying aircraft and for ground defence.
2. ENEMY TACTICS
(a) High-Level Bombing Attacks
These took place generally between heights of 16,000 and 20,000 feet. Bombers approached their targets in close protective formations until running up to the line of bomb release, when formation was changed to line astern (if there was a definite objective to the attack). Attacks frequently occurred in waves, each wave flying at approximately the same height and on the same course. On engagement by H.A.A. guns, avoiding action was taken in three stages:
Stage 1. The bombers gained height steadily and maintained course and formation.
Stage 2. Formations opened out widely and maintained course.
Stage 3. Under heavy fire, formations split and bombers scattered
widely on different courses. It was after this stage had been reached that the best opportunity was provided for fighters to engage.
Low-Level and Dive-Bombing Attacks
In the latter stages of the enemy air offensive numerous instances of low-level and dive-bombing attacks occurred, in particular against fighter aerodromes (Manston, Hawkinge, Lympne, Kenley). [This refers notably to Phases i and 2 of the main offensive as defined in the text.]
L.A.A. and H.A.A. employed in dealing with these forms of attack met with varying success, but in cases where no planes were brought down the effect of fire from the A.A. defence almost invariably disconcerted the dive-bomber so that few bombs were dropped with accuracy.
Considerable efforts were made by Me. 109's and Ju. 87's to destroy the balloon barrage at Dover, and, though at times they partially succeeded, excellent targets were provided for the Dover H.A.A. and L.A.A. guns.
3. PART PLAYED BY H.A.A. GUNS
Targets of all types presented themselves to H.A.A. sites, ranging from solid bomber formations to single cloud-hopping- or dive-bombers, balloon-strafers or hedge-hoppers, all of which were successfully engaged by appropriate methods of fire.
The action of the defence achieved success in the following ways:
(a) The actual destruction or disablement of enemy aircraft (see Appendix C). [Not reproduced; but see Section 7, below.]
(b) The breaking up of formations, thus enabling the R.A.F. to press home attacks on smaller groups of bombers.
(c) Destroying the accuracy of their bombing by forcing the enemy aircraft to take avoiding action [and in general to fly higher than they would otherwise have flown.]
(d) By pointing out to patrolling fighters the whereabouts of enemy formations by means of shell bursts.
The following methods of fire were in operation at this period:
(i) Each gun site was allotted a zone of priority, and responsibility for opening fire on a target rested with the G.P.O.
(ii) Targets could be engaged by day if identified as hostile beyond reasonable doubt or if a hostile act was committed. By night, failure to give recognition signals was an additional proviso.
(iii) It was the responsibility of the G.P.O. to cease fire when fighters closed to the attack.
Unseen firing at this time was in its infancy and considerable initiative was displayed in evolving methods for engaging targets unseen by day or by night.
The following methods were employed:
(i) Geographic Barrages
Many forms of barrage were used by different G.D.A's, but all were based on obtaining concentrations at a point, on a line, or over an area, through which the enemy aircraft must fly.
Suitable barrages for lines of approach and heights were worked out beforehand. Approach of enemy aircraft was observed by G.L. and, by co-ordination at G.O.R's, the fire from each site could be controlled to bring a maximum concentration of shell bursts at the required point.
(ii) Precision Engagements
Method A. Due to poor visibility or wrong speed-settings searchlight intersections were often made without actual illumination of the aircraft. By obtaining slant range from G.L. and following the intersection on the predictor, sufficient data were available to enable shells to burst at or near the intersection.
Method B. This provided for engagement without searchlight intersections. Continuous bearings and slant ranges from the G.L. were fed into the predictor and engagement of target [was] undertaken on the data thus provided. For sites which were not equipped with G.L. the appropriate information was passed down from G.O.R.
It will be appreciated that procedure varied with different Gun Zones, according to circumstances and the equipment available. It should be remembered that all engagements of unseen targets were subject to the express permission of the Group Controller at Uxbridge [acting for, and sometimes under the immediate supervision of, the Group Commander], so that danger of engaging friendly aircraft was obviated.
(c) Anti-Dive-Bombing Barrage
Special barrages against dive-bombers were organised round the following V.P.'s: Harwich Harbour, Thameshaven Oil Installations, Tilbury Docks, Chatham Dockyard, Sheerness Dockyard, Dover Harbour, Purfleet Oil and Ammunition Depots.
This barrage [i.e., any of these barrages] could be employed at any time at the discretion of the G.P.O. when he considered that other and more accurate methods were unlikely to be effective. The barrage [i.e., each barrage] was designed for a height of 3,000 feet and assumed a dive angle of 600. It was based on a barrage circle round each gun site, which was divided into four quadrants in which the barrages were placed.
The maximum effort from H.A.A. guns was required from the 19th August to the 5th October, during which time the crews had little rest, continuous 24 hours manning being required at Dover, a 'duty gun station' system being worked in all areas.
Evidence is available to show how time and again enemy bombers would not face up to the heavy and accurate fire put up by gun stations. Particularly worthy of mention are two attacks on Hornchurch aerodrome, when on both occasions fighters were on the ground for refuelling. A.A.
fire broke up the formation and prevented any damage to the station buildings and aircraft on the ground.
4. PART PLAYED BY L.A.A. GUNS
The targets which offered themselves to L.A.A. guns were in the main small numbers engaged in dive-bombing or low-level attacks on V.P.'s. Opportunity usually only offered fleeting targets, and quickness of thought and action was essential to make fullest use of the targets which presented themselves.
Success against targets by L.A.A. guns was achieved in the following ways:
(a) The destruction or disablement of enemy aircraft (see Appendix C). [Not reproduced; but see Section 7, below.]
(b) The prevention of accurate bombing causing the bombers to pull out of their dive earlier than they intended.
Methods of firing employed by L.A.A. guns [were] as follows:
Fire was directed by No. 3 Predictor or by Forward Area Sights; some Bofors were not equipped with the predictor, when the latter method only could be used.
The predictor-equipped guns require a 130-volt A.C. electric supply which was provided either from engine-driven generators or from the mains. Shooting with the predictor achieved very great accuracy and the results and destruction of aircraft and the average ammunition expenditure proved the efficiency of this equipment (see Appendix C). [Not reproduced; but see Section 7, below.] The F.A.S. method permitted quick engagements of targets although without the accuracy afforded by the predictor.
(ii) 3-inch 20-cwt. Guns (Case I)
Some V.P.'s were equipped with the 3-inch 20-cwt. gun without predictor, which was fired from deflection sights; shrapnel was normally used. H.E., however, was used for targets at greater height.
Lewis guns on A. A. mountings proved extremely effective in attacking low-flying enemy aircraft. These guns were mounted in single, double or quadruple mountings and were fired by the Hosepipe method using tracer ammunition.
(iv) Hispano 20-millimetre Equipment
A few of these weapons only were deployed and, owing to shortage of ammunition and lack of tracer, were not found very effective.
5. PART PLAYED BY SEARCHLIGHTS
Owing to the close spacing of searchlight sites they formed a valuable source of intelligence, and rapid reports were able to be made upwards of
casualties to friendly and enemy aircraft, pilots descending by parachute and other incidents of importance. In addition, they have been able to provide valuable reports of isolated enemy aircraft, trace of which had been lost by the Observer Corps.
The value of the A.A.L.M.G. with which each site was equipped cannot be too highly stressed. [The report adds that, according to claims made and accepted at the time, 23 enemy aircraft were destroyed by A.A.L.M.G's at searchlight sites during the four months under review, this number including a few in whose reported destruction A.A.L.M.G.'s at H.A.A. sites also had a hand. Prisoner-of-War reports showed that it was not generally known by German Air Force pilots that searchlight sites were equipped with A.A. defence.]
Tactical employment of searchlights at night was by either:
(i) 3-beam rule, in which 3 sites only engaged the target; or
(ii) by the Master-beam system, in which one Master-beam per three sites exposed and was followed by the remaining two beams acting under the orders of the Master-beam.
The decision to engage was the responsibility of the Detachment Commander, and no direct tactical control was exercised from Battery Headquarters.
In the early stages of the Battle of Britain night activity was on a small scale and searchlights had few raids to engage. Some illuminations were effected, but throughout it was difficult, by ground observations, to assess the actual numbers. Frequently illuminations were reported by sites not engaging the targets. The difficulty of illumination was increased as the number of night raids increased, owing to the difficulty of sites selecting the same target.
There is evidence to show that searchlight activity, whilst being difficult to measure, forced enemy aircraft to fly at a greater height than they would otherwise have done. Bombs were frequently dropped when enemy aircraft were illuminated, which were possibly intended to discourage searchlights from exposing. Evasive tactics by the enemy consisted of changing height and speed continuously to avoid being illuminated, rather than a violent evasive action upon illumination.
6. G.L. EQUIPMENT
At the beginning of August experiments had just been completed to determine whether G.L. equipment could satisfactorily be used as a Ships Detector. Apart from the results of this experiment three other facts emerged:
(a) The G.L. principle was of considerable value when used in conjunction with searchlights.
(b) That G.L. sets sited in an anti-ship role, i.e., on the top of a cliff, were of considerable value in detecting low-flying aircraft.
(c) It showed the value of small R.D.F. [radar] detectors within the main R.A.F. chain, in plotting enemy aircraft direct to sectors.
At the beginning of the Battle of Britain, 21 G.L. sets were in use by the 6th A.A. Division, and by October this number had been increased by another 14.
(i) G.L. at Gun Stations
The main function of these equipments was to provide data for unseen target engagements as described above. One other function of these sets is worth special mention.
Two sets were specially sited on the cliffs at Dover to pick up targets at low level. These sets were able to register aircraft taking off from the aerodromes immediately behind Calais, thereby obtaining information considerably earlier than it could be provided by the main R.D.F. station on the coast. This information was reported back to Uxbridge Operations Room by a priority code message which indicated the approximate number of aircraft which had taken off and their position. This report was received some five to six minutes before it could be received through the usual R.D.F. channels, and therefore enabled the Controller to order his fighters off the ground correspondingly earlier than would otherwise have been the case. [Moreover the sets were particularly useful on occasions when they escaped the jamming by the enemy which affected R.A.F. radar stations in the neighbourhood.]
This system, which was also adopted somewhat further along the coast in the neighbourhood of Beachy Head, was of all the more value as the enemy were heavily bombing the R.D.F. stations, which were consequently sometimes out of action. [Attacks on radar stations, though infrequent, did sometimes have this effect. Particularly in the preliminary phase of the battle, stations also closed down sometimes while their equipment was being modified or calibrated.]
(ii) G.L. Stations with Searchlights
During the latter stages of the offensive, when the night raids on London commenced, it was realised that the G.L. would be of considerable assistance to night-fighters. An 'elevation' attachment to the equipment was produced and this enabled height to be obtained, which in conjunction with a plotting scheme at S.O.R., enabled searchlight beams to be directed more accurately on a target to assist night-fighters. The results obtained from this were not completely satisfactory, but they showed the way to the development of the present system.
(iii) Mine-laying Aircraft
It was found that the experiments conducted in the ship-detector role could be very satisfactorily applied to detecting mine-laying aircraft which flew in at a height too low to be picked up by the C.H. Stations. It enabled accurate tracks of these aircraft to be kept which were afterwards passed to the naval authorities, who were then able to sweep up the mines which had been laid by these aircraft.
[Section 7 of the Report, and Appendix C to it, record claims to the destruction by the 6th Anti-Aircraft Division, during the period July-October 1940, of 203 enemy aircraft by day and 18 at night. Further statistics in the appendix show that, during the first fourteen months of the war, Bofors light anti-aircraft guns of the division fired 200 rounds for each aircraft claimed as destroyed, heavy anti-aircraft engaging seen targets 298', and heavy anti-aircraft guns engaging unseen targets or employing barrage fire 2,444; and that throughout Anti-Aircraft Command as a whole, the numbers of rounds fired by guns of all classes for each aircraft claimed as destroyed were 344 in July 1940, 232 in August and 1,798 in September.
The numbers of enemy aircraft in fact destroyed by anti-aircraft fire during these periods are not known. Losses sustained by the Luftwaffe in various actions and in the several phases of the Battle of Britain have been assessed by analysis of German administrative records, and are given elsewhere in this volume; those believed to have been sustained by the Italian Air Force during its brief intervention against this country have been taken from an Italian source, and are also given. But (except in a few cases) the German and Italian records do not--and clearly could not--distinguish between losses inflicted by anti-aircraft artillery and those suffered in other ways.
Comparison of claims made by or on behalf of our defences as a whole with losses recorded by the Luftwaffe--not for purposes of propaganda but for administrative ends--shows clearly that, while such claims were often accurate or modest in relatively quiet times, during periods of great activity the punishment taken by the enemy was nearly always exaggerated, sometimes grossly. Irrespective of nationality, the same is broadly true of claims made by or on behalf of air forces or air defence systems in all campaigns which have come within the author's notice, and where material exists for a comparison with recorded losses.]
8. GROUND DEFENCE
Preparations were made by all A.A. defences to assume a secondary ground-defence role; Bofors were provided with anti-tank ammunition, and sited to cover approaches to aerodromes, V.P.'s etc. Certain 3.7-inch guns suitably sited were given an anti-ship role, and preparations were made for barrages to be put on certain beaches. Under the immediate threat of invasion in May 1940, mobile columns of A.A. troops were formed, but these troops reverted to their A.A. role before the Battle of Britain began.
9. LESSONS LEARNT
(a) The outstanding lesson learnt from this intensive air attack was undoubtedly the soundness and suitability of the organisation and arrangements of the control and direction of the anti-aircraft defences. These measures, devised in peacetime and perfected during the earlier and quieter period of hostilities, stood the severe test with amazing resilience and adaptability. No major alterations in the system were indicated or,
indeed, were made subsequent to these operations. [A footnote in the original points out that this statement applied only to the higher organisation, and did not mean that no improvements were made in the control and direction of anti-aircraft gunnery.] The way in which the activities of the anti-aircraft linked in and were capable of co-ordination with the major partners in the venture--R.A.F. Fighter Command, No. 11 Fighter Group, and sector commands--is perhaps worthy of special note.
(b) Other lessons learnt are by comparison of minor import. Chief among them was the great vulnerability of aircraft if caught by accurate H.A.A. fire when in close formation. A good instance of this occurred in an action on the 8th September, when a Geschwader of 15 Do. 17's, flying in formation at 15,000 feet [in fact half a Gruppe; the establishment of a Geschwader was about 90 aircraft] approached a gun site south of the river Thames. The opening salvo from the four 3.7-inch guns brought down the three leading aircraft, the remaining machines turning back in disorder, scattering their bombs on the countryside in their flight to the coast.
The value of H.A.A. fire as a means of breaking up bomber squadrons to enable them to be more easily dealt with by our fighters was demonstrated on numerous occasions in the Thames Estuary.
The importance of A.A. shell bursts as a 'pointer' to fighters, even though the guns cannot themselves effectively engage the enemy, was also frequently demonstrated.
(c) A somewhat negative lesson was the inability of A.A. guns, however well served, completely to deny an area to penetration by determined air attack. Evidence, however, was overwhelming that accurate fire, apart from causing casualties, did impair the enemy's aim, and thus avoid, or at least mitigate, the damage to precise targets. [Moreover even the bare knowledge that certain objectives were defended by anti-aircraft guns tended to relegate the enemy to relatively safe heights, thus imposing on all but the boldest of the attackers a limitation which made accurate bombing harder, narrowed down the problem of defence, and sometimes increased the difficulty of co-operation between day bombers and their escort.]
(d) A rather unexpected result was the high proportion [about one-tenth, according to a calculation based on claims] of planes brought down by A.A.L.M.G. fire. It is doubtful, however, whether with the increased armour now carried by enemy aircraft this lesson still obtains.
(e) The value of training in recognition was repeatedly emphasised throughout these operations. Fortunately, very few instances of friendly aircraft being engaged occurred. Apart from the accuracy of the information as to movement of aircraft furnished to gun sites, this was no doubt due to a reasonable standard in recognition having been attained.
It was, and still is, continually brought home to the A.A. gunner that, before all else, he must not engage a friendly aircraft. With this thought firmly impressed on the G.P.O., some instances of late engagement or failure to engage perforce occurred. In some cases, had the standard of training been higher, to permit the earlier recognition of a machine as 'hostile beyond reasonable doubt', the number of machines destroyed would have been increased.
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