The Flying Bomb - The Defence of ANTWERP and BRUSSELS

TNA Catalogue Reference: WO 205/999

THE FLYING BOMB
THE DEFENCE OF ANTWERP AND BRUSSELS

OCTOBER 1944 TO APRIL 1945

H.Q. G.H.Q. A.A. TROOPS, MAY 1945

[Distribution list attached.]

Gallery Album The Flying bomb, The defence of Antwerp and Brussels | WW2Talk

 

INDEX

PART I - DIVER Defence of Antwerp and Brussels
SECTION I - Events leading up to the attack.
SECTION II - Direction of attack.
SECTION III - Restricted area.
SECTION IV - Deployment and reinforcement.
SECTION V - Early warning.
SECTION VI - Communications.
SECTION VII - Equipment and fire control.
SECTION VIII - Radar.
SECTION IX - Ammunition.


PART II - Analysis of the Attacks.
SECTION X - Course and direction.
SECTION XI - The target.
SECTION XII - Times of attack.
SECTION XIII - Height and speed.
SECTION XIV - Confirmation of claims.
SECTION XV - Effectiveness of A.A.
SECTION XVI - Total destroyed.
SECTION XVII - Ammunition.
SECTION XVIII - Rounds per bird.
SECTION XIX - Fall of shot.
SECTION XX - Scale of attack.


APPENDICES
APPENDIX A - Instruction No. 16
APPENDIX A - Annexure 1, Siting of Radar equipment
APPENDIX A - Annexure 2, Ideal Layout for Defence
APPENDIX B - Incidence of Attack
APPENDIX C - Average Height and Speed
APPENDIX D - Table
APPENDIX E - Ammunitions Expenditure, Claims and Rounds per Bird


DIAGRAMS
DIAGRAM N1 - Belgium DIVER Area 2nd April to 10 April 1945
DIAGRAM N2 - Belgium DIVER Area up to 1 February 1945
DIAGRAM N3 - Belgium DIVER Area 1 February to 10 March 1945
DIAGRAM N4 - Belgium DIVER Area 10 March to 2 April 1945
DIAGRAM O - DIVER A.A. Defences at time of greatest Deployment
DIAGRAM P - Early Warning DIVER Defences
DIAGRAM Q - A.A. DIVER Wireless Communications
DIAGRAM R - DIVER Line Communications Skeleton Diagram
DIAGRAM S1 - DIVER Lane 7 to 21 November 1944
DIAGRAM S2 - DIVER Lane 21 November to 21 December 1944
DIAGRAM S3 - DIVER Lane 21 December 1944 to 21 January 1945
DIAGRAM S4 - DIVER Land 21 January to 21 February 1945
DIAGRAM S5 - DIVER Land 21 February to 21 March 1945
DIAGRAM S6 - DIVER Land 21 to 30 March 1945
DIAGRAM T1 - Incidence of Attack, First & Second Month
DIAGRAM T2 - Incidence of Attack, Third & Fourth Month
DIAGRAM T3 - Incidence of Attack, Fifth & Sixth Month
DIAGRAM U - Height
DIAGRAM V - Speed
DIAGRAM W - DIVERS destroyed by A.A.
DIAGRAM X1 - Rounds per bird
DIAGRAM Y1 - DIVER Fall of Shot, First Month
DIAGRAM Y2 - DIVER Fall of Shot, Second Month
DIAGRAM Y3 - DIVER Fall of Shot, Third Month
DIAGRAM Y4 - DIVER Fall of Shot, Fourth Month
DIAGRAM Y5 - DIVER Fall of Shot, Fifth Month
DIAGRAM Y6 - DIVER Fall of Shot, Sixth Month
DIAGRAM Z1 - DIVER Scale of Attack, October to January
DIAGRAM Z2 - DIVER Scale of Attack, January to March

 

PART I
DIVER DEFENCE OF ANTWERP AND BRUSSELS

SECTION I - Events leading up to the attack.

1. In early September 1944 it became clear that the possibility of DIVER attacks against targets on the Continent was more than theoretical. Adequate supplies of flying bombs were available to the enemy since his air launched attacks against the UNITED KINGDOM had used far less than the rate of consumption for which he must have provided. Construction of launching sites West of the RHINE was suspected and targets were available, sufficient in importance and size.

2. On 10th September 1944 the problem was raised at a meeting of the 21st ARMY GROUP A.A. Defence Committee, and Commander G.H.Q. A.A. Troops was ordered to investigate the defence of ANTWERP and BRUSSELS against DIVER.

3. Four main aspects of the problem required solution:-
the likely scale of attack and the layout and resources required for an adequate defence,
the restrictions upon guns and aircraft necessary to ensure reasonable freedom for both,
the need for providing reliable early warning where the advantages of a static radar chain and an observer corps did not exist, and finally
the equipment required to compete with the particular target presented by the flying bomb.

4. To some extent the answers to the problem could be obtained from the experience gained in the attacks on ENGLAND. But the absence of the ENGLISH CHANNEL, between launching sites and target, made the problem in BELGIUM fundamentally different. And this difference afftected two of the main parts of the problem mentioned above:
early warning and the restrictions to flying and shooting.
Both these subjects are discussed in more detail later (Sections III and V).

5. The very wide arc, from which firing could take place, made necessary far more guns than were available. So great was the commitment, that it precluded any possibility of deploying an effective defence round the whole of the threatened perimeter even with the extra guns made available from American resources. As a result it was necessary to make a firm plan to block the most likely lines of approach, based on the best available intelligence. Thereafter adjustments would have to be made when the attack developed or subsequently changed.

6. The equipment problem was largely a matter of pressing for a sufficient quantity of SCR 584 and No. 10 predictors. This had been outstandingly the most successful equipment in ENGLAND, and was accordingly demanded on the highest priority. The first fifteen sets arrived from ENGLAND ON 6th October and another six on 12th October before the attack started.

7. On 15th September reconnaissance began of the proposed BRUSSELS gun belt.

8. A preliminary appreciation was made and was sent to 21st ARMY GROUP on 23rd September while the preparation continued of an instruction for issue to units. (Procedure Instruction No. 16, attached as Appendix A). As a result of this appreciation the A.A. Defence Committee met on 30th September and, after consideration, agree the proposed plan. It was also agreed that the defence must be an A.A. task entirely. The ROYAL AIR FORCE with too few airfields or suitable aircraft, were unable to take part.
9. It is clear that the total requirements in A.A. guns could not possibly be met from British sources.

Accordingly, while reconnaissance began on the ANTWERP belt, a request was made to S.H.A.E.F. on 2nd October to provide three U.S. A.A.A. gun battalions as reinforcements. At the same time, the units required for the preliminary scale in the BRUSSELS gun belt were ordered to twelve hours’ notice.

10. On the following day S.H.A.E.F. agreed to provide the three gun battalions, to be ready to move at seven days’ notice. During investigation it had become clear that the defence of the two vulnerable areas was a joint problem and layouts were worked out on this basis.

By the same token proposals for a combined restricted area were put to Second T.A.F. for agreement or discussion.

11. In order to try out early warning, communications and siting, one British A.A. Brigade was ordered to carry out a skeleton deployment in the ANTWERP gun belt.

12. The A.A. Defence Committee met again on 13th October and agreed the following scales of defence, as proposed by G.H.Q. A.A. Troops:-

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It was also decided that, for the moment, VT fuzes (also known as POZIT or PETER fuzes) would not be used. On the same day an appreciation of the possible scale of attack was received from Second T.A.F. Maximum daily launchings were estimated at 100, to start any time. In view of this, Brigades were ordered to prepare at once for deployment at short notice.

13. S.H.A.E.F. were requested to dispatch the three gun battalions and this was done on the following day, 15th October.

14. Since the scales agreed by the Committee were beyond the maximum possible even with three U.S. gun battalions, and since the sixty sets of SCR 584 already demanded were the maximum allotted under Lease-Lend, reinforcement was necessary with further U.S. units. As ANTWERP was to be a combined British-United States port, with our Allies unloading the greater tonnage, it was felt that it was reasonable to ask for their further assistance in its defence. Accordingly a request was made to S.H.A.E.F. on 18th October for total reinforcements of twelve gun and six A.W. battalions. This was agreed. Half were to move immediately, the remainder to be earmarked for the task when the threat materialised.

15. On the following day a Conference of all U.S. and British Commanders was held at G.H.Q. A.A. Troops to check the plans for deployment. It was agreed that ANTWERP DIVER defences (to be known as ANTWERP X) should be an American command and BRUSSELS (BRUSSELS X) a British command.

16. The first U.S. A.A.A. Group, with three gun battalions under command, was given orders for deployment and was instructed to superimposed its units immediately on the existing British skeleton layout.

17. At 0915 hours on 21st October 1944 the first flying bomb crossed BRUSSELS from the South-East and, departing towards GHENT, landed in open country. Before 0600 hours on 22nd October three others followed it to land very wide to the South-West of BRUSSELS. Preparations being completed, all available defences were ordered to deploy immediately.

 

SECTION II - Direction of attack.

18. Before the attack started it seemed reasonable to suppose that the angle of approach would extend from North HOLLAND to as far South up the RHINE as range permitted. The extreme Southerly point expect was in fact in the area of TRIER. The range from TRIER to ANTWERP is 140 miles.

19. Since accuracy tends to increase in inverse ration to range, the shortest rout seemed the most likely, and the area West of the RHINE between the RUHR and COLOGNE the most probable. Moreover from this direction a short increase in firing range would allow the launching sites to be put behind the RHINE with added safety and simplification of supply problems.

20. North and North East HOLLAND also appeared to have advantages. Range is not overlong and the absence of natural obstacles would permit a lower height of operation. Moreover the course would not pass over German territory, and range permitted the erection of sites well East of the RHINE and behind its protection.

21. There still existed the possibility of attack from the East and North. Due East was the thickly populated RUHR, but it was possible that some sites might begin to operate from this area or immediately North or South of it. Any sites erected in the North in HOLLAND, would suffer serious supply difficulties by our interdiction programmes on the line of the IJSSEL. Nevertheless an attack of limited intensity would so seriously affect the gun density of the defences as to make it a profitable course of action for the enemy to adopt.

22. A further possibility lay in the use of air launched attacks from the North West and South. This was not likely to develop to any great extent as long as such launchings were able to be directed against LONDON with little loss.

23. In the event, the attack was divided into there main phases. From 21st October to 14th December the main launching area was between BONN and TRIER and all but a few bombs were fired from there. At the beginning of the period a small number was despatched from immediately East of METZ but this ceased with the UNITED STATES advance over the area. It was never more than a fraction of the total attack.

24. On 16th December a new launching area became active in the North East, round DEVENTER, ALMELO and ENSCHEDE. The new course partly by-passed the defences until redeployment could be efected and this accounted for the increased effectiveness of the attack for a brief period. Bombs still continued to be launched from the South East but for the most part in decreasing numbers although on one or two exceptional days the majority of the activity was from this area.

25. On 27th January the third main phase opened and the first bomb appeared from due North from the area of ROTTERDAM. Despite the reduced range the attack was little more effective that that from the North East, although more accurate.

26. At intervals bombs were launched from East of the RHINE from sites between COLOGNE and BONN, but the contribution was exceedingly small and never effective.

27. Detailed figures and recorded radar tracks of the directions of attack are given in PART II Section X.

 

SECTION III - Restricted area.

28. A large part of the success achieved against DIVER in ENGLAND was due to the freedom of fire allowed to A.A. guns within their zone of engagement. Before the Continental attack began, the need was stressed for a similar freedom for the guns of 21st ARMY GROUP. In A.A. Command guns had been shooting over the sea and friendly aircraft could be routed away from them.

29. In BELGIUM to achieve similar freedom involved the establishment of an area restricted to aircraft between the front line and the bases of two supporting air forces. This was bound to conflict with Air Force requirements. It also involved unrestricted A.A. fire over airfields, troop concentrations, administrative installations and large towns, which was bound to be unpopular. Certain compromises were therefore necessary.

30. When discussions began with the Air Force early in October with particular reference to ANTWERP and BRUSSELS, it was evident that a completely prohibited area running North and South to the East of both towns imposted an intolerable restriction on friendly flying for operations, and would mean abandoning the use of airfields within the prohibited area.

31. Worse still, the area proposed fell across the inter-Army Group boundary and affected both British Second TACTICAL AIR FORCE and the American NINTH AIR FORCE. The problem was further complicated by the presence within the proposed prohibited area of the town of LOUVAIN, of certain ROYAL AIR FORCE ammunition and petrol dumps and, later, of FIRST CANADIAN ARMY roadhead.

32. These dangerous areas on the ground were safeguarded, where necessary, from winged flying bombs and falling fragments by not firing directly over them, under the terms of G.H.Q. A.A. Troops Procedure Instruction 16 (See Appendix A). It was agreed that no special precautions need to be taken in respect of the dispersed roadhead area.

33. The problem of the safety of friendly aircraft was much more acute. As our own aircraft were unable to take any part in the actual destruction of DIVER, no allocation of zones for fighter and gun operations was needed. Agreement on the exact restrictions to be observed by aircraft and guns in the DIVER area was in the end only reached after a meeting held on 31st October at S.H.A.E.F.

34. The area finally determined was intended to cover DIVER approaching through an arc bounded by WESEL in the North and KOBLENZ in the South. It was bounded as shown on Diagram N and was operative above this height and guns would not fire above 5,000 feet. A corridor was allowed to aircraft of SECOND TACTICAL AIR FORCE only, through the centre of the area. This corridor is also shown on the diagram. Special arrangements, visible on the diagram, were made for aircraft using airfields B64 (DIEST) and A89 (LE CULOT).

35. The result was to split the area into three parts.
Area A North of the corridor was not intended for use unless a threat from the North East developed.
Area B compromised the remainder of the area North of the corridor and was intended primarily for the defence of ANTWERP.
Area C, South of the corridor, was intended for the defence of BRUSSELS.

36. To ensure that friendly aircraft, by night, avoided the restricted area and to help them to find their corridor, searchlights were placed as marker beacons at certain points roughly 12 - 15 miles apart. Those on the perimeter of the area were ordered to point outwards at an angle of 60 degrees to the horizontal and the three marking the corridor to expose vertically, flashing agreed letters at regular intervals.

37. Briefly the rules for engagement were absolute prohibition of flying by day and night in Area B except that the controller might order “HOLD FIRE” for aircraft in distress, any order for HOLD FIRE to involve the least possible restriction on guns. Area C was to be an IAZ by night and at any time of the day when the controller at A89 (LE CULOT) airfield authorised it. At other times of day aircraft based on A89 were to be allowed to cross Area C and engagement of DIVER was to be by identification only.

38. To ensure the safety of friendly aircraft still further, engagement above 5,000 feet was forbidden even on recognition and guns deployed for defence against DIVER were no allowed to engage any other type of target.

39. These arrangements were finally put into force on 4th November. Experience of their operation showed two main difficulties -
the problem of infringements of the prohibited area by friendly aircraft, and
the varying arc of approach of the targets.

40. The number of infringements at times reached alarming proportions although strenuous efforts were made by the Air Forces concerned to check them. They resulted, however, in many false alarms for the guns. The number of engagement of friendly aircraft was kept surprisingly low in the circumstances.

41.The arc of approach of the targets was originally from further South than had been anticipated and during the first week of November it was clear that some bombs launched from the TRIEER area were by-passing the South-West corner of the restricted area and so reaching BRUSSELS unmolested. Area C was therefore extended, by agreement with the Air Forces concerned, to include a projection in this corner (marked as Area D on Diagram N), and guns were redeployed accordingly.

42. When in mid-December the attack suddenly started from the extreme North East it was clear that it could not be met merely by implementing the projected Area A. A revised area was therefore approved and became effective on 20th December. This area is also shown on Diagram N. Provision had to be made in this extended area for landing aircraft at two further airfields B70 (DEURNE) and B77 (GILZE). The area North of the corridor was in future known as Area B and that South of it as Area C.

43. Occasionally, targets flying above the permitted height of engagement (5,000 feet) reached the vulnerable area. In order not to extend the prohibited area in height, agreement was reached on 17th December to engage targets above 5,000 feet and North of the corridor on visual recognition only.

44. At the end of January 1945, attacks on ANTWERP started from due North. This new threat involved redeployment of the defences and a Westward extension of the restricted area. The extension proposed carried the Westward boundary of the area to a line running, in general terms, North and South through BERGEN-OP-ZOOM. This extension would have deprived the Air Force of all access to B70 and B79 (HOOGERHEIDE) airfields. It was therefore agreed to exclude B79 airfield and its Western approach rout from the area and to provide a corridor across Area A following the road from ANTWERP to TURNOUT. Both the exclusion and the corridor were operative by day only. It was also agreed that B79 should be evacuated at the earliest possible moment. By 22nd February, however, the Air Fore had withdrawn from B79 and it was no longer necessary to make special provision for access to it from the West. Details are also shown on Diagram N.

45. By mid-February, the threat of attack on BRUSSELS from the extreme South East had ceased in view of the American advances. The part of Area C, previously known as Area D and added on 11th November, was therefore cancelled. At the same time the South East corner of Area C was reduced to an unrestricted area, by local arrangement with the American Air Force, who wished to operate their aircraft with safety over this area from A89 and Y10 (LE CULOT EAST) airfields.

46. B70 airfield was abandoned by 10th March. The ANTWERP - TURNHOUT corridor could thus be closed and a further extension made of Area A to the South-West. At the same tim, in order to avoid unnecessary infringements or engagements of friendly aircraft by day and to improve the field of fire of the South East defences of ANTWERP, the line of the Southern corridor was also amended to follow the main road BRUSSELS - LOUVAIN - DIEST. This new corridor did not follow a straight line and so naturally caused difficulties for aircraft homing by beam on B58 (MELSBROEK) airfield by night. Special provision was made for a HOLD FIRE on request from the Air Force to allow such aircraft to home direct from DIEST.

47. A further slight extension to Area A was made on 19th March since targets fired from due North of ANTWERP might carry on towards BRUSSELS and protection of BRUSSELS from this threat was needed.

48. As the Allied armies advanced over the launching sites and lines of supply, successive reductions in the DIVER restricted area were made to allow the fullest freedom to aircraft in conformity with the changing situation. On 2nd April it was clear that a threat to BRUSSELS no longer existed and the already truncated Area C was cancelled, as was that part of Area B South of the Northern boundary of the original corridor. On 10th April the advances to the North East made possible the cancellation of all that part of Area A lying South East of a line joining TILBURG to MALINES. This change was the last mutilation of the DIVER area. It was finally cancelled when the X defences were stood down on 20th April.

49. The changes to the restricted area are shown diagrammatically in Diagram N as follows:-
(a) BELGIUM DIVER AREA showing amendments in force until 1st February 1945.
(b) BELGIUM DIVER AREA as at 1st February 1945 showing change up to 10th March 1945.
(c) BELGIUM DIVER AREA from 10th March 1945 to 2nd April 1945.
(d) BELGIUM DIVER AREA as at 2nd April 1945, showing final change made 10th April 1945.

 

SECTION IV - Deployment and Reinforcement.

50. On 22nd October the BRUSSELS defences were deployed. On the following day the first flying bomb was directed at ANTWERP. The build up of the ANTWERP X layout began, with the deployment on 24th October of the first three U.S. gun battalions under on A.A.A. group headquarters. On 27th October the first U.S. A.A.A. brigade arrived to command ANTWERP X defences. By 28th October S.H.A.E.F. had authorised U.S. reinforcements up to twelve gun battalions and three A.W. battalions. On 2nd November the second three gun battalions completed deployment, making a total of six deployed on that date.

51. As anticipated, further units to thicken the BRUSSELS gun belt were also needed. Since no further reinforcements were available, War Office was asked to add six H.A.A. Regiments to the 21st ARMY GROUP Order of Battle.

52. The attack was switch to BRUSSELS on 8th November and a further H.A.A. Regiment was deployed in the gun belt, making a total of five H.A.A. Regiments. On the following day the attack returned to ANTWERP. On 10th November the second U.S. A.A.A. Brigade, which had arrived on 7th November, assumed command of the ANTWERP X defences. The British command of the BRUSSELS X defences had been established since 22nd October.

53. To complete the ANTWERP X layout the three U.S. A.W. battalions were deployed on 8th November, the third group of three gun battalions on 12th November and the last three on 15th November. The American ANTWERP X defences were all under the operational command of G.H.Q. A.A. Troops, although remaining the administrative responsibility of IX Air Defence Command.

54. At this date the strength of the completed gun belts, in regiments/battalions, was:-

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It soon became clear that really low level attacks were not likely and that L.A.A. was therefore, to some extent a luxury. Scales were reduced accordingly.

55. Searchlights were used for L.A.A. engagement, for warning and for assisting G.P.O.s in tactical control by giving a visual picture. When excessive shell clutter made visual laying of H.A.A. equipment more accurate, they were a material help to H.A.A. engagement. They were also needed as marker beacons, to denote the boundaries of the restricted area and the corridor through it.

56. During December the position was governed by three principal factors:-
(a) The growing importance of ANTWERP as a target at the expense of BRUSSELS, coupled with the increase in this commitment in view of the appearance of attacks from the North-East.

(b) The arrival of mixed H.A.A. regiments from ENGLAND for deployment in BRUSSELS X in relief of male units.

(c) The abortive offensive by von RUNSTEDT in the ARDENNES at the end of the month.

57. Four U.S. A.A.A. gun battalions had to be withdrawn from ANTWERP X for ground shooting in the ARDENNES battle and the remaining units of both ANTWERP and BRUSSELS X defences were prepared to adopt a ground role immediately if an emergency arose. The scale of H.A.A. Regiments or gun battalions, however, never fell below:-
ANTWERP X - 8
BRUSSELS X - 4

With the failure of the German offensive the four gun battalions soon returned to ANTWERP X.

58. As attacks on BRUSSELS continued to decease, it was decided in January that the original target figure of eight H.A.A. Regiments in BRUSSELS X defences could be reduced to five and the remaining searchlight battery removed. During December and early January the three mixed regiments had taken over their share of this commitment.

59. British units had meanwhile joined the U.S. units in the ANTWERP X defences. Originally on 23rd December three troops of the normal ANTWERP A.A. defences were given a secondary DIVER role. During January the first British H.A.A. Regiment was placed under tactical command of the U.S. A.A.A. brigade.

60. Attacks on ANTWERP were now coming from three directions and the defences were fully extended. By 14th February it became necessary, therefore, to nominate a British A.A. brigade Headquarters to administer and organise the following British units under American tactical command:-

Four H.A.A. Regiments
One S.L. Regiment
One L.A.A. Troop
One local warning Troop.

61. With the addition of one British H.A.A. Regiment to ANTWERP X, the following scale of regiments/battalions was reached and remained, subject to slight fluctuation, while the full thread lasted:-

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62. By the end of March it was evident that the only surviving threats were from the North and North East. The advance into GERMAN had overrun possible launching sites in the East and was taking large numbers of Prisoners, all of whom needed guards. A preliminary reduction of four U.S. A.A.A. gun battalions was therefore made, to provide men for guarding these Prisoners.

63. By mid-April an effective threat to BRUSSELS had clearly ceased to exist and the North-East approach to ANTWERP was already markedly reduced. The routes of supply to the Northern launching sites were also growing less and less reliable. As the calls for manpower elsewhere were increasing, 21st ARMY GROUP A.A. Defence Committee decided on 13 April to close the BRUSSELS X defences and to reduce the ANTWERP X scale to:-

Four U.S. gun battalions
Three Battalions H.A.A. Regiments

64. Orders implementing this decision were issued on 16th April, but on 18th April S.H.A.E.F. decided that further attacks were so improbable that authority could be given to stand down all the remaining defences from 20th April.

Note: Diagram O shows a typical layout of the gun belts at the time of maximum deployment

 

SECTION V - Early warning.

PROBLEM
65. It was originally intended that the army should only provide supplementary early warning for DIVER defences to augment the existing Air Forces early warning system. Suggestions for deploying P.P.I. radar stations (Type 14 or IW) for this purpose were made in G.H.Q. A.A. Troops Procedure Instruction No. 16 (see Appendix A).

66. It soon became clear, however, that the requirement was fourfold:-

(a) Earliest possible warning of targets immediately approaching the vulnerable area.

(b) Accurate and up to date plotting for putting-on gun radar.

(c) Analysis of tracks of targets engaged, to ensure that both early warning system and gun layout covered the right arcs, and to forecast as far as possible impending changes in the direction of attack.

(d) Identification of targets by any possible means, of which recognition of their characteristic appearance or sound was the best.


PASSAGE OF INFORMATION
67. In order to meet these requirements in full a revised system was developed incorporating army and ROYAL AIR FORCE resources in three belts:-

(a) The outer belt, -of ROYAL AIR FORCE wireless observer units (WOUs) designed to give a minimum of eight minutes (48 miles) warning and identification.

(b) The inner (putter-on) belt, -of army radar stations (Type 14), designed to give four minutes (24 miles) warning.

(c) The identification belt, of army observer posts with wireless communications, designed to give immediate identification to guns in Area C, where identification was essential before engagement.

68. In order to tie up the various sources of information strict synchronised timing was necessary, for which B.B.C. time signals were used.

69. Other broadcasts from operations rooms controlling various types of warning were fed into the system, notably IX Tactical Air Command (VERVIERS) and 25 Sector R.A.F. (EVERBERG), to help cover blind spots. It was necessary, however, to ensure that these operations rooms only issued information derived from their own sources and did not duplicate other information with a time lag, so giving the impression that two targets existed in place of the single one that was really there.

70. Thus the earliest warning on a target might derive either from VERVIERS or from the WOUs. It would in any event be identified by them and an indication of its location at that time would be passed to the Type 14 station covering that arc. The Type 14 station would then follow the target until it could be picked up by the gun position radar.


ORGANISATION
71. The outer belt was a purely Air Force organisation, compromising ten WOU posts, with two controlling LW (light warning) stations with facilities for passing information both to the inner belt and direct to all four AAORs in the gun belts.

72. The inner belt consisted of up to nine Type 14 stations, the exact number in action varying from time to time. Two separate tracking stations were also deployed in the inner belt in the earlier stages of the deployment. Each of these stations was based on a Type 14 set (Radar A.A. No. 4 Mk V) but in order to ensure that the station remained in action in all weather conditions, it proved necessary to include two LW sets (Radar A.A. No. 4 Mk II) with each station. At certain key stations two Type 14 sets were deployed at critical times. Each station of the inner belt could pass information direct to all four AAORs.

73. The inner belt was thus a large commitment. To meet it, a new organisation was formed consisting of two local warning radar troops ROYAL ARTILLERY, each troop to operate four stations. In the peak periods the resources of these troops had to be supplemented by Type 14 sets found from elsewhere.

74.The identification belt consisted of twelve observer posts deployed originally some 23,000 yards ahead of the heavy A.A. gun belt and later advanced to 50,000 yards ahead. This belt was organised as an identification troop ROYAL ARTILLERY. Both the local warning and the identification troops were new organisations designed and formed at short notice in the theatre, to meet the requirements of DIVER defence.

75. These specially formed units were British organisations but the local warning troops covered both the British and American defences. The identification troop met a requirement in the British system for which the American organisation uses the AAAIS detachments, forming part of the AW battalions. AAAIS detachments covered all lines of approach in the ANTWERP X layout.

76. The basis of this system was established by the end of November and formed a permanent framework adaptable to changing requirements.

77. WIth so many difficult sources of information there was a risk that the defence would be swamped. The information differed widely both in reliability and time lag. Early in December 1944, therefore, 159 AAOR at ERPS QUERBS was converted into an experimental filter room in order to reduce the congestion of communications, equipment and plotting personnel in all four AAORs. It was later decided that a full-dress filter room would tend to increase the time-lag unacceptably and the arrangement was therefore revised. 150 (U.S.) AAOR and 159 AAOR were designated “master AAORs” for ANTWERP X and BRUSSELS X respectively. A direct link between these AAORs was established by a plotter from 150 to 159 AAOR and vice versa. The master AAOR was therefore able to present complete information for its own sector of the defences, from which the plotter from the other sector could select and pass such information as seemed likely to be of use to his own AAOR.

78. Apart from changes in locations as a result of different directions of attack and reinforcements made necessary by shortcomings in radar or communications equipment, the system described above stood the test of operations. But it was essential that it should be flexible enough to meet constantly changing conditions of attack and should at the same time be able to be superimposed from outside on to the normal resources of AAORs and units, which could never have done the job by themselves.

Note: The system is illustrated in Diagram P.

 

SECTION VI - Communications.

79. In the early stages wireless was used, but line communication was always established as soon as possible. The utmost use was made of existing underground and overhead civil lines. The system is described in the following paragraphs and diagrams showing the wireless and line communications at the time of widest deployment are attached as Diagrams Q and R.

80. Type 14 radar stations to AAOR

(a) Initial stages - by RT direct from radar operator to AAOR plotter by No. 12 set at the radar station (with remote control in the radar cabin) to R107 set at AAOR. Due to lack of supplies of No. 12 sets, No. 33 sets had to be used at those Type 14 stations nearer AAOR. A medium wireless section (ROYAL CORPS OF SIGNALS) was provided to operate the No. 12 / No. 33 sets at each Type 14 station.

(b) Permanent system - by line wherever possible, using existing underground and overhead civil lines to the utmost. Lines from civil line test points were always ‘built’ lines, either poled spaced double D8 or 70 lb Cd Cu route. Distances involved made “repeatering” of circuits necessary. Where civil lines did not exist and distances between radar stations and AAOR were great, wireless communication was retained. Wireless links were retained as ‘stand by’, when line communications were established.

81. American Air Force operations rooms to AAOR

(a) Initial stages - by RT (American wireless equipment) to R107 set at AAOR.

(b) Permanent system - similar to that used between Type 14 station and AAOR. Line communication from IX TAC operations room at VERVIERS to all AAORs was soon established. One line from XXIX TAC Operations Room at MAASTRICHT to 150 (U.S.) AAOR (Master AAOR ANTWERP X defences) was eventually established.

82. Wireless observer unit control posts to AAOR

(a) Communications were originally provided by the Air Force over wireless links, but were later taken over by the army owing to difficulties of provision of Air Force equipment and personnel.

(b) Owing to the distance ahead of AAOR at which WOUs operated, a short time lag between the receipt of the plot and its being passed to the AAOR plotter was acceptable. RT was therefore not necessary and WT communication with No. 33 sets was accepted.

83. AAOR to gun positions and L.A.A. troops

(a) Initial stages - by wireless broadcast from No. 36 set at AAORs (American No. 339 sets at American AAORs) to receivers at gun positions.

(b) Permanent system - by line to H.A.A. gun positions and L.A.A. troop headquarters. Few of these lines could be provided from existing overhead or underground cables with the result that large quantities of 7 pair cable and field quad cable were in use, producing a heavy line maintenance commitment.

84. Identification troop to gun positions

(a) From each identification troop post to troop headquarters - by No. 36 set to its own R208 set.

(b) From identification troop headquarters to gun positions (after coordination of information) by No. 36 set broadcast to R208 sets.

85. DIVER AAORs to normal AAORs
Lines were provided from the master AAOR of ANTWERP X to adjacent AAORs engaged in normal A.A. defence, so that the latter could take part instantly in the DIVER battle should it be suddenly extended to new vulnerable areas.

86. Line communication with searchlight marker becons
During the enemy offensive in the ARDENNES and while the threat of airborne attacks on Belgian objectives persisted, it was necessary to arrange for the SL marker beacons to be doused at short notice. Line communication was therefore provided to link the beacons with some position or station which was itself in direct line communication with an AAOR.

 

SECTION VII - Equipment and fire control.

INITIAL EQUIPMENT

87. Before the attack began, British H.A.A. units were all equipped with 3.7-inch mobile guns, with GL 3B (Radar A.A. No. 3 Mk 2) and Predictor A.A. No. 1 using either GL 2 (Radar A.A. No. 1 Mk 2) or LW (Radar A.A. No. 4 Mk 3) as a “putter-on” for the GL 3B.

88. American H.A.A. units were equipped with 90mm (power controlled) mobile guns with SCR 584 (Radar A.A. No. 3 Mk 5) and Director M9 (Predictor A.A. No. 10).

89. L.A.A. units all held 40mm guns, the British controlled by Stiffkey sticks (sights correction Mk 5) and the American by the No. 3 predictor. The No. 3 predictor had been abandoned by British units at an early stage in the planning of the invasion.

90. One British L.A.A. Regiment had been equipped with triple 20mm guns on mobile platforms for the assault phase and was still holding this equipment in the theatre. Each American 40mm gun detachment was also equipped with a quadruple .50 calibre equipment.


EQUIPMENT FOR DIVER DEPLOYMENT

97. Laying on the target at night with the 40mm gun proved difficult and a method of illuminating the sights was devised. This proved helpful and has been adopted as a modification.

98. The existing system of L.A.A. fire control was reconsidered in order to produce a predicted concentration of fire on a fast moving target. Trials were conducted in the control of four 40mm guns by GL3B and No. 1 predictor, modified for the purpose. These trials showed signs of success initially but it became clear finally that this equipment could only be a makeshift until the No. 7 or No. 10 predictor, with appropriate radar control, could be made available to L.A.A. units. It was thought that the provision and training of men for such a makeshift was unjustified and the project was abandoned.

99. Trials with a No. 7 predictor controlling four 40mm guns were started. Owing to equipment failure and lack of spares, coupled with urgent demands for L.A.A. guns in their normal role, these had to be abandoned before reaching the end of the training stage.

100. An equipment deployment of triple 20mm equipments was also made and some Category A successes were achieved. However, the number of targets flying at heights suitable only for L.A.A. engagement did not justify a large scale deployment of this type of weapon.


SEARCHLIGHTS

101. Searchlights were used mainly:-

(a) to provide early warning, facilitate initial radar pick-up and assist tactical control;

(b) to permit visual lay, where extensive shell clutter hindered radar following and obscured visual observation of the flame;

(c) to illuminate targets for L.A.A. fire.

The planned system of belts thus gave place, where searchlight resources and the ground available permitted, to a continuous carpet stretching from the innermost guns to up to 20,000 yards ahead of the forward gun belt along the most likely lines of approach.

102. 150cm Mk 2 searchlight projectors were used and found fully satisfactory at the normal heights of attack. Control pillars were not used, since the rate of traverse required normally exceeded the maximum speed of the control gear (Mk 5).

103. SLC was not used as the increased range of SLC pick up over detection by sound or sight was of no practical value. SLC following in conditions of cloud was, due to the high rate of traverse necessary, found less satisfactory then following by aural means.

104. Marker beacons were 90cm lights wherever possible. It was found necessary to deploy two projectors at each position in order to ensure that one beam was continuously in action.


TACTICAL CONTOL

105. The problem of targets fired in salvoes was only encountered in ANTWERP X defences. Simple rules were introduced to ensure that all targets were engaged. All gun positions were numbered and the following rules were observed:-

(a) When two or more targets were approaching the vulnerable area on parallel courses, each position engaged the target whose plotted course was nearest to its position.

(b) When two followed one another on the same course, odd-numbered positions engaged the first target and even-numbered positions the second.

 

SECTION VIII - Radar.

INTRODUCTION
106. This section is concerned particularly with the use of army radar against DIVER by British units, although much valuable information and advice were obtained from the experience of American units with similar equipment.

107. The three uses of army radar during the DIVER deployment were:-
(a) Fire Control.
(b) Local warning.
(c) Identification.


FIRE CONTROL

108. Equipment
(a) American Units:- SCR 584
(b) British Units:- mainly SCR 584; a few were still equipped with GL 3B.

109. Siting
(a) Radar reconnaissance preceded all original deployments and the proposed layouts often had to be modified as a result.

(b) Natural screening was used to reduce clutter whenever possible but artificial screening by wire netting was needed on some positions. The siting problem was aggravated by the large arc (often up to 90 degrees) within which, on many positions, the attack was suspected.

110. State of readiness
(a) A high state was needed throughout the twenty-four hours, and manning was done in shifts.

(b) On an average each equipment worked for 20 to 22 hours a day and the maintenance roster covered the whole layout.

111. Performance
(a) The flying bomb is a small, fast-moving target and in the early stages in BRUSSELS X, cases occurred of a bomb coming in undetected by radar (both GL 3B and SCR 584). Similar failures occurred when mixed regiments with static guns were first deployed with their own SCR 584 equipments. Investigation showed that neither siting nor operators could be blamed.

(b) The inference is that newly deployed equipments were not initially in correct adjustment. Only after a target had been missed was the need for adjustment suspected. Once the equipment had been adjusted to give successful results it was relatively easy to keep it in adjustment.

112. Modifications
For the SCR 584, two modifications in particular were found to be of great value for the engagement of DIVER:-

(a) “N-squared gate”, to allow tracking through the shell clutter caused by the very high concentration of bursts near the target.

(b) “16-pole changeover switch”, devised for use in place of the official cloud switch to allow a quick changeover from radar to visual tracking.

113. Screening
Artificial wire-net screening was often necessary. Owing tot the frequent and rapid redevelopments, a lighter form of screen than that used in ENGLAND was developed with the help of AORG and the components were produced locally.


LOCAL WARNING

114. The part played by army radar in the provision of local warning has been described in SECTION V. Good warning proved extremely difficult from radar equipments working overland, because of the low height of the target and the poor echo obtained.

115. Experience obtained in ENGLAND with Radar A.A. No. 4 Mk 5 showed that this equipment would function best with the aerial system horizontal and action had already been taken to obtain the necessary modification parts.

116. At the start of the attacks it was expected that the range of detection of DIVER overland would be:-
(a) Radar A.A. No. 4 Mk 3 (LW) - 25,000 yards
(b) Radar A.A. No. 4 Mk 5 (Type 14) (aerial horizontal) - 45,000 yards

117. These equipments were, therefore, first deployed about 40,000 yards forward of the gun belt on the expected lines of approach. Each early warning station normally comprised one Radar A.A. No. 4 Mk 5 and two Radar A.A. No. 4 Mk 3. The latter were needed to cover periods during which the 10cm equipments were out of action from excessive cloud or ground clutter.

118. Two Radar A.A. No. 4 Mk 3 were provided to allow for one always being out of action, since this equipment was known to be unreliable. Three of these equipments were really desirable, to make sure of one being always in action, but it was impossible to provide so many.

119. Various methods of siting were tried. Eventually, in the relatively flat country, it was found better to use no form of screening and as far as possible to take advantage of ground reflection (i.e. flat ground out to 1,000 yards distant from the set with no woods or other major obstructions). Better results were obtained if the equipment was sited on the line of approach rather than to a flank.

120. The range of detection varied considerably and the reliability (percentage of targets detected out of those presented to the equipment) was often poor. It was found that these variations could nearly always be ascribed to variations in the overall sensitivity of the equipment. This often changed during a single day. The falling-off in performance was seldom noticed until a target had been missed. The only solution to this problem was to introduce during watches frequent checks on permanent echoes.

121. In view of the poor average reliability (about 63 per cent) it had been decided that two Radar A.A. No. 4 Mk 5 would have to be deployed at each station. They would have to be worked simultaneously and with recurrence frequencies synchronised by using a common motor alternator set. A start had been made to implement this policy when the attacks ceased.

122. Thus the early warning station, which, as first conceived, consisted of only one radar set, increased to four or five. The object was to keep two 10cm sets continuously in action, with one 212 Mc/s set always ready to take over.


IDENTIFICATION

123. Experience was needed to distinguish infallibly a DIVER break on a radar tube, from that, for example, of a fighter homing direct on an airfield. Identifications normally had to be confirmed from evidence of sight or sound.

124. In the hope of finding a foolproof method of radar identification, the sub-assembly known as the “propeller modulation unit” (DU65) was fitted to Radar A.A. No. 4 Mk 5 and proved of considerable value.

125. As further DU65 equipments were not available a local modification was devised and it was decided to fit the modification to all Radar A.A. No. 4 Mk 5 deployed for early warning against DIVER but the attacks ceased before the modification could be introduced generally.

 

SECTION IX - Ammunition.

PROBLEM

126. H.E. ammunition was used by both H.A.A. and L.A.A. guns. With the latter there was no problem.

127. The problem of H.A.A. ammunition was in two parts:-
(a) Employment of time or VT fuzes.
(b) Supply.


EMPLOYMENT OF TIME OR VT FUZES

128. VT fuzes had proved very successful in ENGLAND, where they were fired over sea areas only. They have great advantages in lethal effect but also certain disadvantages. Their use would have increased the danger to civilians and military installations from blind shell and low airburst caused by low angle firing or by malfunctions of the fuze. In a highly populated area, well filled with administrative dumps, this factor could not be neglected.

129. In addition, although normal fuzes could be timed to burst within the restricted area, VT fuzes were liable to follow a trajectory outside this area and so to endanger aircraft flying legitimately above 6,000 feet. The danger from such casual fire was not serious but could not be disregarded.

130. Early results showed that with normal ammunition some 70 per cent of targets actually approaching the vulnerable areas were already being destroyed. It was estimated that the improvement to be expected from VT fuzes was about a further 20 per cent. It was debatable, therefore, whether the estimated improvement was worthwhile in view both of the disadvantages and of the high rate of destruction already being achieved.

131. After balancing the various factors, it was initially agreed that the use of VT fuzes was not justified. As the threat increased, however, this decision was reversed. S.H.A.E.F. authority for the employment of VT fuzes had already been issued on 15th December and they were finally taken into use on 17th January against visually recognised targets only.

132. On 18th February the use of VT fuzes was extended to cover engagement of all targets in ANTWERP X.

133. The use of VT fuzes was still subject to minimum QE limitations. Owing to these limitations, the use of fuze T98 with 3.7-inch guns was not considered worthwhile. As T149 (the fuze with short self-destruction element) was not available in time, only American units eventually used VT fuzes in the BELGIUM DIVER area.

134. Experience showed that minimum QE could be reduced with safety and the following figures were finally accepted, although with more experience further reductions might have been possible:-

T98 (3.7-inch long) 25 degrees
T149 (3.7-inch long) 12 degrees
T74 (90mm long) 330 mils
T152 (90mm short) 165 mils (subject to a maximum engagement range of 12 seconds)

135. The effect of the minimum QE was that two or three types of fuze might be used in the same engagement, - time fuzes up to the minimum QE for VT fuzes, then T152 up to the minimum QE for T74 (165 mils) and finally T74 if the target passed above 330 mils. The reason for the change from T152 to T74 was a shortage of the former.


SUPPLY

136. A study was made of the quantities of ammunition expended each day in A.A. Command between the end of June and the beginning of September. The resulting figures were reduced to rounds per gun and, by comparison with the actual scale of attack on the days concerned, an estimate was reached of the likely figure for a daily scale of 100 launchings. After allowance had been made for difference in equipment (e.g. the absence of automatic fuze-setters) and in rules for opening fire, it was considered that 20 rounds per gun per day was a fair average scale for engagement of DIVER. Tot this figure was added half the normal scale of 6 rounds per gun per day for engagement of aircraft. Calculations for replenishment were based therefore on a total expenditure of 23 rounds per gun per day.

137. This figure was never reached, in fact, in the British part of the defences but at one time the American ammunition expenditure became very large (some seventy rounds per gun were expended on one day). This increased expenditure coincided with a period of difficult in replenishing 90mm ammunition and very nearly proved disastrous. But during the critical time supply just managed to keep ahead of demand. Expenditure figures are given in Appendix E.

 

PART II - Analysis of the Attacks.
21st OCTOBER 1944 to 30th MARCH 1945


SECTION X - Course and Direction.

138. In Diagrams S1 to S6 are set out summaries of the lines of attack in monthly periods. Initially the tracks were obtained from specially deployed radar stations, whose sole job was tracking, and from similar information from 50 A.A.A. Brigade (U.S.) (ANTWERP X) and FIRST U.S. ARMY. Later they were from accurate radar tracking by SCR 584 employed in the defences. Accurate tracks have been available since 7th November 1944.

139. In the Diagrams, the launching area is divided into arbitrary sectors. Each sector contains in figures the total DIVER recorded across it. The traffic over the receiving and is shown in the same way.

140. The principal ‘lane’ is shaded and the boundaries of the stream are shown by solid lines. Dotted lines show courses which were used from time to time outside the normal stream.

 

SECTION XI - The Target.

141. The first two days of the attack were spent by the enemy in ranging and bombs were scattered widely round BRUSSELS. Thereafter the attack turned on ANTWERP and, with a few exceptions during the earlier period, the latter remained the target.

 

SECTION XII - Times of attack.

142. The incidence of attack during the twenty-four hours is shown in Diagrams T1 to T3 as a series of polar graphs. Each graph covers one month. Precise figures are also given in Appendix B.

During the first two months of activity the peak period was 0800 - 0900 hours. This was the same as the peak recorded during the attacks on ENGLAND. During the third month it changed to 0700 - 0800 hours and in the fourth it was just before mid-day. During the final period of activity the bulk of the launchings was between 0500 - 0900 hours.

143. For convenience the twenty-four hour period was divided into two parts:-
0600 to 1800 hours called ‘day’ and
1800 to 0600 hours called ‘night’.

The table below shows the total and the rate of launching by day and by night:-

DAY
Flying bombs per hour - 1.6
Number launched - 3,098

NIGHT
Flying bombs per hour - 1.2
Number launched - 2,344

144. In general more bombs were launched when visibility was bad. This was not, however, a universal rule. Many other factors clearly affected the scale and rate of attack.

 

SECTION XIII - Height and speed.

145. Figures for each week are given in Appendix C. The figure for height and speed is the average of all targets measured. In addition, the number of flying bombs, whose height was greater than the maximum permissible for engagement (viz. 5,000 feet), is shown as a percentage of the total scale of attack. All these figures are shown graphically in Diagrams U and V.

 

SECTION XIV - Confirmation of Claims.

146. DIVER claims were made by the unit and confirmed or rejected by the brigade concerned, using the same method as for aircraft. No reference to the Air Force was required. To centralise the adjudication of claims for ANTWERP, a claims board was appointed by Headquarters ANTWERP X. This board consisted of technical officers from both the U.S. A.A.A. brigade headquarters controlling the defences.

147. In the rare cases where the same bomb was claimed by both BRUSSELS X and ANTWERP X, the necessary adjustment was made by H.Q. G.H.Q. A.A. Troops, after investigation.

148. DIVER destroyed were labelled in two ways, - either Category A (airburst) or Category B (brought down short of the target and exploded on the ground). In order to establish a Category B claim units had to prove a marked change in course or behaviour, as well as showing the time and map reference of impact.

 

SECTION XV - Effectiveness of A.A.

149. The effectiveness of the defences can only be assessed by the number of DIVER destroyed out of those which were a direct threat to the vulnerable area, i.e. “approachers”. The total of “approachers” was reached by adding:-

(a) Those which landed in the target (i.e. a circle of 7,000 yards radius).

(b) Those which crossed the target and landed beyond (from the gunner’s point of view these were as great a threat as those which landed in the target).

(c) Those which, if not destroyed, would by their course have crossed the target.

ALL DIVER which did not qualify as “approachers”, were labelled “flankers”.

150. Accurate figures for this calculation were not available until 26th November. Thereafter the percentage of the “approachers” which were destroyed by guns is shown in Appendix D and, as a graph, in Diagram V. The decline around 21st December 1944 was partly caused by the change in direction of attack, which for a time by-passed the defences, and for which incomplete early warning was available. But the most serious cause was the considerable weakening of the ANTWERP defences by the move of units to FIRST U.S. ARMY as reinforcements, during the ARDENNES battle.

151. Appendix D contains the weekly figures of “approachers” to each target, of “flankers”, of the number of each destroyed and of the proportion of the successful claims which burst in the air.

 

SECTION XVI - Total destroyed.

152. During the whole attack A.A. destroyed 2,356 DIVER. Division between the months and between Categories A and B is shown in Diagram W. The figures are also included in Appendix D.

 

SECTION XVII - Ammunition.

153. The total ammunition expenditure by each type of gun was as follows:-

90mm - 426,5519 rounds
3.7-inch - 110,820 rounds
40mm - 55, 244 rounds
20mm - 26, 407 rounds

Full weekly figures are given in Appendix E.

154. In addition 58,589 rounds .5 calibre ammunition were fired. The majority of this was expended in practice firing at operational targets.

155. All 3.7 ammunition was fired with normal time fuzes.

156. Of the 90mm ammunitions, 50,582 rounds were fired with VT/POZIT fuzes (T74 or T152). Since a mixture of POZIT and time fuzes was fired in practically every engagement, it has never been possible to produce reliable figures of the comparative performance of the two (see Section IX para 135). But attention is drawn to the increase in the proportion of airburst claims after the introduction of POZIT and the reduction in expenditure per claim for the 90mm equipment.

157. Throughout the whole period of use these fuzes, no single incident was reported of damage, caused on the ground by their failure to function.

 

SECTION XVIII - Rounds per bird.

158. The rounds per bird for each type of gun are shown in Diagrams X1 and X2, and in Appendix E.