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Chapter 7: Defensive Measures - NEPTUNE Operation

Part 1 - Enemy Naval Dispositions, 1944

1. Before pursuing the adventures of the assault forces, the comprehensive measures executed for their protection and support will be reviewed. The protection of NEPTUNE from enemy counter action was essential to the success of the operation. Allied forces were most vulnerable to enemy counter action when they were embarked and at sea. Some 5,000 allied vessels, carrying approximately nine army divisions with full combat equipment, were at sea at one time.1 These vessels were formed into some 75 convoys and groups, passing along narrow coastal lanes, moving across the channel through the narrow mineswept channels of the SPOUT2 or crowded into the congested confines of the assault area. Had the enemy not been deterred by a comprehensive program of defense, this enormous armada would have presented to enemy air and naval forces a very profitable target.

2. Enemy naval forces available to attack NEPTUNE consisted of two battleships (by D-day, both were seriously damaged), two pocket battleships, one unfinished aircraft carrier, two heavy cruisers, four light cruisers, thirty-seven seaworthy destroyers, eighty-three torpedo boats, and some 200 U-Boats.3 In addition, the enemy had some 215 miscellaneous small war vessels stationed in or near the channel.4


1 For numbers, formation and organization of these vessels, see ON 1, Appendix II, III, IV and ANCXF Report, Para. 2. For details of numbers of convoys, see ON 7, Appendix 1, ON 16, Section B, and ON 9. This great number of convoys lasted for only a few days just before and just after the assaults. During the Build-Up, however, the extraordinary average of 32 Convoys and smaller groups was maintained. See ANCXF Report, Para. 64.

2 The routing and movement of the assault forces is discussed in detail in Chapter VI, Section 3. The SPOUT was the name given to the system of cross channel convoy lanes. Its northern end, which was about 10 miles wide, was located about 15 miles south of NAB Tower (near Portsmouth) and marked by the "Z" buoy. Its southern end, which was about 30 miles wide, debauched into the assault area at 49°40' north latitude. Convoys hugged the coast line until they reached the northern end of the SPOUT; they then turned south and crossed the channel in various lanes within the SPOUT.

3 This was the estimate of enemy naval strength as of 1 Nov 1943, made by the U.S. Chiefs of Staff in CCS 300/3 of 18 Nov.43. The estimates for destroyers and below were only approximations.

4 This was the estimate for February 1944, given in XFNP Page 3.



3. It was assumed that once the enemy was aware that the Allies had committed themselves to the Normandy invasion, he would expend his forces ruthlessly in an attempt to defeat it. His heavy units in the north were not expected to be used directly in the Channel area, except, possibly, as a last desperate measure. They were likely, however, to make diversionary sorties into the Atlantic. But his light surface forces might be concentrated in the Channel against NEPTUNE. These forces were expected to restrict their attacks to darkness or periods of low visibility, and to operate primarily on the assault and convoy flanks. Enemy U-Boats were expected to concentrate rapidly in the Channel and its western approaches and to operate without regard to loss. The enemy also maintained a mine barrier along the continental coast line, and was expected to undertake further offensive and defensive minelaying, especially in sea areas around the U.K. assembly areas and the assault areas, both by aircraft and naval minelayers.

4. The allied naval plan to defend NEPTUNE against the enemy naval threat was:

a. To prevent distant enemy forces from moving toward the approaches to the Channel,
b. To seal off both ends of the Channel, so that enemy forces in its environs could not penetrate,
c. Within the Channel, to patrol the flanks of the Convoy route, and to screen the assault area against enemy channel based forces,
d. To escort each and every convoy,
e. To sweep sea mines out of all waters required for NEPTUNE forces, and
f. To defeat enemy air attacks by an integrated program of air cover and AA defense.


A. Plan for Minelaying

5. In order to assist in the protection of allied vessels engaged in the assault, naval and air forces executed an extensive minelaying operation (known as Operation MAPLE), with the general purpose of impeding the movement of hostile vessels against the invading forces. The objects of Operation MAPLE were:

a. To impede the movement of light enemy vessels stationed inside the Channel,
b. To impede ingress into the Channel by enemy naval forces situated in the Atlantic and North Sea,
c. To compel enemy naval forces moving toward the NEPTUNE area to follow a course to seaward of the extreme range of enemy shore batteries and shore based fighter cover, in order that allied surfaces forces would be free to intercept their progress,
d. To disrupt enemy shipping generally during the critical period, in order to reduce seaborne movement of enemy reinforcements and supplies toward the battle area.

6. Minelaying was carried out by the following naval forces:

(a) HMS Apollo, (b) HMS Plover, (a) 10th, 50th, 51st and 52nd M.L. Flotillas, (d) 9th, 13th, 14th, 21st, 22nd and 64th M.T.B. Flotillas. In addition, mines were laid from the air by Halifax, Sterling and Lancaster bombers of numbers 1, 3, 4, 5 and 6 Groups, Bomber Command, R.A.F. Command of the Minelaying operation was exercised by the normal authorities responsible for minelaying in British home waters. The Naval forces were accordingly under the direction of the Commanders-in-Chief, The Nore, Portsmouth and Plymouth, and the Admiral Commanding, Dover. Minelaying aircraft were under the direction


1 For details of NEPTUNE minelaying, see XFNP, Appendix-XVII and ANCXF Report, Appendix 15.


of the Air Officer Commanding-in-Chief, Bomber Command. General control of all minelaying authorities was exercised through the usual Admiralty Channels. Coordination between the minelaying operation and the general NEPTUNE naval plan was arranged by ANCXF, who stated his requirements and coordinated the general plan. The MAPLE minelaying plan was developed by ANCXF and is set out in his naval plan Appendix XVII. Mines were laid with the object of:

a. Creating normal hazards to enemy shipping,
b. Endangering enemy light craft, and particularly E and R-boats,
c. Presenting the enemy with a difficult minesweeping problem.

The supply of mines was arranged by the Admiralty.

7. With the exception of the field laid in the Straits of Dover, and an area mined by aircraft to the north of the Frisian Islands, all the minefields were offensive in character. The two semi-defensive minefields, referred to above, were intended primarily to counter any movement of enemy heavier forces from the east. Dormant preparations were also made to reinforce these fields, and to lay mines in the Kiel Canal or its approaches (Operation BRAVADO).

B. Minelaying Operations

8. The Operation was divided into six phases:

Phase (1)
(up to 17 April) Normal minelaying operations were executed by naval minelayers and aircraft, using standard mines;

Phase (2)
(17 April - 9 May) Routine offensive laying with standard mines was continued, and, in addition, special types of mines were introduced into fields laid off Ijmuiden, the Hook, the Scheldt, Boulogne, Fecamp, Le Havre, the Brittany coast and the Frisian Islands. A proportion of the mines laid were timed to become effective at various dates so as to escape being swept before the operation was due to begin.


Phase (3)
(9 May - 28 May). Operations continued as in phase (2), with additional fields being laid in the vicinity of Ushant, and on the general line between the Gasquets and Ushant. Minelaying with special mines, timed to become effective at varying dates, was augmented in the fields to the north of Le Havre and to the north and northwest of Cherbourg. During this phase, aircraft executed an extensive series of minelaying operations in the Kattegat, Baltic Heligoland Bight, Frisian Islands, and in the Bay of Biscay, with the object of retarding the movement of enemy vessels from these more distant waters toward the Channel and assault area. On the night of 12/13 May, a minelaying operation was executed by Mosquito aircraft in the Kiel Canal. Similar operations were executed on the nights of 15/16 and 26/27 May, when mines were laid by aircraft in the approaches to Aarhus, Aalborg and The Sound, as a counter to possible enemy movements from Norway. As these operations involved some risk of compromise to the new types of mines, it was not originally intended that they should be laid from aircraft before 20 May. But to enable full advantage to be taken of especially suitable minelaying conditions, this date was anticipated by five days in the minelaying in the Baltic.

Phase (4)
(29 May - 4 June). During this phase, operations were primarily directed to the laying of special mines off Ijmuiden, the Hook, the Scheldt, Calais, Le Havre, Cherbourg, St. Malo, Morlaix, Brest, and the Biscay ports. Aircraft also executed further lays off Aalborg and in the approaches to Aarhus.

Phase (5)
(Nights of 5/6 June). Operations in Phases 1-4, were, of necessity, related to a fixed date. Those in Phase 5, on the other hand, were planned to be carried out concurrently with the assault. The original plan provided for the laying of mines: (a) off Point de Barfleur, (b) southwest of Le Havre, (c) off Etretat (in conjunction with Operation TAXABLE), and (d) off St. Malo. In the event, only the lay off Etretat was executed. In view of the shipping congestion in the approaches to the assault


area and the resulting complication of the projected lays, the other D-day minelaying operations were abandoned.

Phase (6)
(6 June onwards). During this phase, the majority of the Coastal Force minelayers were diverted to escort and patrol duties. Further limited operations off Le Havre were executed, however, under the direction of NCETF. Aircraft continued to lay mines off the Channel, Biscay, the Channel Island ports, as a deterrent to the use of these harbors by U-Boats.

9. During the course of Operation MAPLE, a total of 6,850 mines were laid. Of these, 42% were laid by naval forces in 66 operations and 58% were laid by aircraft in 1800 sorties.1 These operations made an effective contribution to the general immunity from surface and U-Boat attack enjoyed by the assault forces. A considerable number of casualties were inflicted on the enemy, and his minesweeping organization was stretched to the limit. Minefields in the vicinity of Ushant and off the Brittany coast had the desired effect of driving U-Boats into open water, where they could be dealt with by allied anti-submarine forces. The special operation in the Kiel Canal resulted in a complete dislocation of the enemy organization at an important moment. The entire operation cost the allied cause, in casualties, only one Motor Torpedo Boat 2 and 19 minelaying aircraft.



Mines Laid Areas
Baltic and Kattegat
Heligoland Bight and Frisian Islands
Ijmuiden to Brest
Biscay Ports
Coastal Forces


2 On the night of 18/19 May, MTB 203 struck an enemy mine off Etaples and was sunk. Casualties were one missing and five injured.


A. Countering the German Heavy Fleet

10. The major distant naval threat was from the German heavy fleet and associated units stationed in Norwegian and Baltic Waters. In November 1943, these forces consisted of two Battleships (one seriously damaged), two Pocket Battleships, one unfinished Carrier, two Heavy Cruisers, 4 Light Cruisers, from 16 to 25 Destroyers, and miscellaneous lighter vessels.1 Between November and invasion day, these forces were further reduced by constant air and naval attacks.

11. The allied force charged with the responsibility of guarding NEPTUNE from these forces, was the British Home Fleet stationed at Scapa Flow and operating in the North Sea and North Atlantic. Between 5 - 9 June 1944, the Home Fleet in Scapa Flow consisted of three Battleships, three Fleet Carriers, seven Heavy Cruisers, 12 Destroyers, and numerous miscellaneous light forces.2 With it were associated Number 18 Group Coastal Command (R.A.F.), and various long distance heavy bombing formations of Bomber Command.

12. This force was obviously adequate to deal with any movement of the German heavy forces of the north. Indeed, it had stood guard against them throughout the war. Little, if any, coordination with ANCXF and SCAEF was required, and control of the distant naval cover against this threat was


1 CCS 300/3 of 18 November 1943.

2 The balance of the Home Fleet was on duty in the Channel in immediate support of OVERLORD. The ships at or working out of SCAPA were:
2nd Battle Squadron: Duke of York, Anson, Howe.
Fleet Carriers: Furious, Indomitable, Victorious.
Cruisers: (1) 1st C.S. - Kent, Berwick, Devonshire, (2) 10th C.S. - Bermuda, Jamaica, Sheffield.
3rd Destroyer Flotilla: Milne, Marne, Matchless, Meteor, Musketeer, Wager, Wakeful, Wessex, Whelp, Wizard, Volace, and Nubian.



retained by Admiralty working through the normal command channels of the Home Fleet. Throughout the critical first days of the invasion, the German heavy forces in the north failed to react, and the Home Fleet did not even have the opportunity to repel an attempted "rush" toward the channel area.1

B. Countering U-Boat Movements From the North

13. Another threat from distant enemy naval forces was that, when the invasion began, U-boats stationed in the north might be transferred to the Channel. Admiralty assigned CinC Western Approaches responsibility for guarding against this threat.2 He (CinC Western Approaches) provided a force consisting of three escort carriers3 with associated aircraft, and six groups of naval escort, stationed some 130 miles westward of Lands End.4 This force, operating in conjunction with Coastal Command, maintained a constant surveillance over the U-Boat transit area. In the event, few contacts were obtained, and by 10 June, four of the escort groups were transferred for use inside the Channel.5


1 The quiescence of the German fleet in the north may be explained in part by any or all of the following: (1) Fuel shortage. On 5 June 1944, the allocation of fuel to the German Navy was cut 33%. Fuel issued to submarines was not cut so that the heavier units absorbed a proportionately larger share of the cut. (2) The battleships were damaged and the cruisers were being used primarily for training. (3) The German High Command expected the main allied landing later and in the Low Countries and gave their orders accordingly. (See Admiralty NID 24/2 65/45, p.45, p. 42-43.

2 No direct channel of command between ANCXF and SCAEF and CinC Western Approaches was required or provided, in order to achieve the necessary coordination of effort for this task.

3 Tracker, Pursuer and Emperor.

4 Approximately 50° 30' North 9° 00' West.

5 This operation was known as operation "C A".



C. Sealing the Western Channel

14. The task of sealing off the western channel approaches from U-Boat or other penetration, was assigned to CinC Plymouth, who was to operate under the general direction of ANCXF.1 The strength of enemy forces based in the Brittany and Biscay area, which were available to be sent against NEPTUNE via the western approach, was estimated to be five destroyers, five torpedo boats, 80 to 90 miscellaneous light war vessels and 130 U-Boats. It was thought that the enemy might be able to reinforce his U-Boats to about 200.2

15. In order to prevent these forces from penetrating into the Channel, where they could menace the flanks of the convoy routes, CinC Plymouth organised a sea barrier, known as the "CORK", in the western reaches of the channel.3 ANCXF allotted to CinC Plymouth the following forces with which to seal the CORK: 12 fleet destroyers,4 four MTB flotillas,


1 See Chapter III for a detailed account of the command relations between the Channel Home C's in C, ANCXF and Admiralty.

2 See ON I Para. 10; ONI, Appendix VII Annex K; CinC Plymouth NEPTUNE Report, Section 2, Para. 21. There are striking discrepancies in the figures shown in the above sources, especially on the question of U-Boats. CinC Plymouth reckoned that there were no more than 40 odd immediately available on D-day. The balance, perhaps, may be accounted for by the fact that some were on other operations, some never got down from the north, and that a ratio of 60% was the maximum available at any time for sea duty.

3 The CORK was bounded on the east by the eastern limit of the Plymouth Command (a line running from Portland Bill, to Cap de le Hague). It was bounded on the north and south by the coasts of Brittany and Cornwall and on the west by a somewhat intermediate line at about 7°00' west longitude.

4 These were the 19th R.N. Destroyer Division composed of: Tartan, Ashanti, Hiada and Huron; the 20th R.N. Destroyer Division composed of: Blyscaiwica (Polish), Eskimo, Piorum (Polish), Javelin; and the 18th U.S. Destroyer Division, composed of Davis, Somers, Jowett plus Emmons. See ON 5 & ON I, Appendix II, Section A.



comprising 34 craft plus 3 U.S.N. P.T's. and 4 anti-submarine support groups. In addition to this, Coastal Command aircraft of Number 19 Group, with its attached R.N. and U.S.N. formations, operated to CinC Plymouth's requirements.

16. The first step taken to seal the CORK was the laying of extensive minefields along the west coast of Brittany astride the enemy's coastal route. The object of this mine barrier was to compel enemy U-Boats and other vessels to detour sufficiently to seaward to be outside the range of German fighter cover, in order to allow allied air and naval forces an unmolested opportunity to attack them.1

17. On the night before D-Day, the general disposition of these forces was as follows:

a. One Destroyer Division carried out a constant patrol in the Hurd Deep2 in order to arrest any possible attempt by the enemy to rush a strong U-Boat pack up the middle of the Channel;
b. A second destroyer patrol, known as the "Western Patrol", was organized so as to operate with four destroyers in an area about 50 miles north of Ushant.3 The object of this patrol was to intercept enemy vessels, and, especially, destroyers proceeding from the Gironde toward NEPTUNE;
c. The U.S. destroyers and, at night, light coastal forces of Plymouth command, were posted to seaward of the exposed western arm of Force U's. convoy route, and were supported by special air patrols;


1 For details of the minelaying program, See Section 2, Chapter VII.

2 The Hurd Deep is located in mid-channel, directly south of Devon. The patrol operated between 50° 12' North, 2° 21' West, and 49° 56' North, 3° 16' West.

3 Since the main enemy destroyer force was still in the Gironde on the night before D-day, this patrol was not manned until the night of 6 June (night following D-day) when air reconnaissance showed that enemy destroyers were moving northward.



d. The entire area was patrolled every thirty minutes by aircraft.1

18. This general plan for sealing the CORK, though modified to fit special requirements, was continued throughout NEPTUNE and afterward.2 Enemy destroyers in the Bay of Biscay did not begin to move against NEPTUNE until the evening of June 6 (some 15 hours after the landings). They were brought to action in the early hours of June 9, when four of them departed Brest in the general direction of the Channel. At 0120, they were intercepted 20 miles northwest of the Ilde de Bas, by the 10th RN destroyer Squadron, which sank one, drove another ashore, and damaged a third. The latter, in company with the fourth, escaped to Brest. This action virtually ended the threat to NEPTUNE convoys from attack by enemy destroyers. On the night of 4/5 July, destroyer patrols damaged three gun boats in the vicinity of Morlaix. On the night of 12/13 June, they carried out the diversionary operation ACCUMULATOR in the Channel Island area.3 During the first two months of NEPTUNE, constant attacks of opportunity were executed against coastal transport.4

19. Anti-U-Boat operations in the CORK were conducted by the combined Air-Navy patrol. The results obtained by naval forces were not spectacular from the point of view of "kills", but they were, none the less, highly successful in that they achieved their principle object of stopping the U-Boats from arriving in the convoy lanes. During the first two months, no NEPTUNE losses were known to have been caused by U-Boats.


1 For details of those air operations, see Chapter VII, Section 8.

2 One exception to this, was that the U.S. destroyers were withdrawn after the assault phase. See ON I, Appendix II, Section B.

3 See Chapter II, Section 5 and Chapter VIII, Section 9.

4 For details of these inconspicuous but, by no means, unprofitable operations, see CinC Plymouth's NEPTUNE Report, Section 2.



D. Sealing the Straits of Dover

20. The task of sealing the eastern end of the Channel was less difficult, as the Dover Straits are narrow and do not exceed 20 miles breadth at some points. They are well guarded, not only by numerous British coastal batteries, but also by extensive stretches of unnavigable shoal water. Moreover, German naval forces available to penetrate the eastern barrier were not formidable. The enemy disposed in the southern reaches of the North Sea, southward of the barrier interposed by the Home Fleet, of no more than 30 E-Boats, 65 R-Boats, 40 Minesweepers, and some 45 miscellaneous small vessels. No U-Boats, Torpedo Boats, Destroyers or heavier units were situated in these waters.1 There was, however, a remote possibility that some six Destroyers and ten Torpedo Boats from the Baltic and the Bight might attempt to elude the patrols of the Home Fleet.2

21. Under the general supervision of ANCXF, the Admiral Commanding Dover was responsible for sealing the eastern Channel.3 His first concern was to assure that the allied minefields, on the enemy's side of the Straits and elsewhere astride enemy convoy routes, were strengthened and kept up to full effectiveness.4 From the forces assigned him for his various NEPTUNE tasks, he disposed ten squadrons of coastal craft as a constant guard against miscellaneous vessels which might try to penetrate into the Channel. He also 5


1 See ON I, Appendix VII, Annex K.

2 See ON I, Para.11. Should those forces be so employed, the enemy heavy forces would have no screen in case they put to sea. It was, therefore, considered unlikely that they would be sent to hazard the dangers of the Home Fleet Patrols and to try to penetrate the Channel barrier.

3 For details of command arrangements, see Chapter III.

4 Details of minelaying operations (MAPLE) are given in Chapter VII, Section 2.

5 ON 1, Appendix II, allotted V.A. Dover: (1) 4 destroyers (2) 39 M.T.B's. (3) 10 M/L's. (4) 8 Minelaying M/L's. (5) 4 M/S (6) M/L's.



stationed his four destroyers, whose basic task was to guard the east wall of the SPOUT and the eastern arm of the Force L convoy route, in such a manner that they could be quickly drawn into the Straits in case of an unexpected sortie by German destroyers or torpedo boats. In addition, strong air formations of Number 16 Group, Coastal Command, operated to the requirements of A. C. Dover, and maintained constant air surveillance over the entire area of the Dover Straits.1

22. The enemy's reaction in the Dover area, however, was limited to making preparations to arrest the expected future assault against the Pas de Calais and the Low Countries.2 No attempt was made to thrust naval forces through the Straits of Dover.

E. Patrols Along the Convoy Flanks

23. A system of screening patrols was organised to protect the channel convoy lanes from attack. Enemy naval forces within the Channel consisted of one destroyer, four torpedo boats, seventeen E-Boats, five R-Boats four minesweepers, eighteen light gun craft, some thirty-seven minesweeping trawlers, some thirty-four patrol vessels and seventy-five harbor defense craft.3

24. Under the general direction of ANCXF, CinC Portsmouth was responsible for operating the patrols on the western flank of the SPOUT; the Admiral Commanding Dover, for those on the Eastern flank.4 To man the patrols, ANCXF assigned to CinC Portsmouth, four R.N. fleet destroyers,5 two frigates


1 See Chapter VII, Section 8 for details of air cover.

2 Admiralty N I D 24/T, 65/45.

3 See ON I, Appendix VII, Annex K.

4 To put this arrangement into effect, the boundary between the Portsmouth and Dover commands was altered on 28 May 1944 for operational purposes from the line Dungeness-Dieppe to a line from Worthing (which is located some 20 miles east of Portsmouth to a position 50°00'N, 0° 15'W, thence to 49° 40'N 0° 00' W, thence due east to the French Coast.

5 Onslow, Onslaught, Oribi and Offa.



and five flotillas of coastal forces, comprising 39 craft. He assigned to A.C. Dover, four R.N. fleet destroyers1, two frigates, and ten flotillas of Coastal forces, comprising fifty-four craft.2 In addition to these naval forces, Number 19 and 16 Groups, Coastal Command, R.A.F., operated to their general requirements. Bombers carried out several devastating strikes against enemy naval bases and ships in port.3

25. During the course of the war, an elaborate and efficient chain of radar stations had been developed along the entire southern coast of England. Those gave A.C. Dover complete radar coverage of the Channel in his area, while CinC Portsmouth had coverage more than half-way across the Channel. To bring the southern edge of his area of the Channel, which included the assault area, under radar surveillance, CinC Portsmouth posted four frigates, mounting powerful radar instruments somewhat to the south of mid-Channel. Radar information was fed into central plots, from all shore stations and from the radar frigates. Portsmouth and Dover were thus able to maintain up to the minute locations and movements of all objects in the Channel, and to vector patrols against hostile vessels.4

26. The patrols were disposed as follows:

a. A seven mile gun zone was established on either side of the SPOUT. Any ship found within this zone during darkness was to be presumed hostile. Allied vessels were to enter only in hot pursuit of the enemy;


1 Savage, Opportune, Obedient and Orevell.

2 For ANCXF's assignment of these vessels, see ON 5, Appendix II, Section A and B. It will be recalled that a part of Dover forces were to enable him to establish the eastern Channel barrier as well as to man the Channel patrols.

3 See Chapter VII, Sections 8 and 9 for details on air patrols.

4 The Channel in CinC Plymouth area was so wide that he had to rely on air reconnaissance to direct his ships into the vicinity of enemy vessels.



b. The destroyers were to patrol along the outer edges of the gun zone: these systems of patrols were known as the East and West Walls of the SPOUT;
c. Dover's destroyers patrolled in single units along a line from Dungeness to the east wall to seaward of the coastal channel;1
c. Coastal forces, which were employed primarily during the night or periods of reduced visibility, were stationed, or carried out patrols as required.


1 This was in order to cover the SPOUT, the coastal channel and, at the same time, to be able to cover the Straits.


A. Allied Naval Dispositions

27. ANCXF assigned to the appropriate Task Force Commander the task of screening the assault area against enemy naval penetration.1 Enemy naval forces within the Channel consisted of an indeterminate number of human torpedoes, self-exploding pilotless surface craft, sea mines to be laid by aircraft, and the 195 miscellaneous vessels in the preceding section.

28. To repel these enemy forces, the Task Force Commanders established an area screen, detailing to it, a proportion of the vessels allotted them by ANCXF. Manning the area screen required a careful phasing in the use of vessels. Until allied forces arrived in the assault area, there was no screen. On arrival, a proportion of the escorts and patrol vessels took up screening patrols. Still later, other vessels, which had completed their initial tasks of boat control, close fire support, or some other job, took over patrol duties, while a proportion of the escorts returned to the U.K. in company with the convoys. In due course, most vessels capable of escort duty, were transferred to CinC Portsmouth for escort duty to facilitate his task of operating the post assault build-up convoy program.2


1 See ON 9, Para. 21, 27, 28 and 29. It will be recalled that ANCXF held naval command over the entire Channel area during the assault. Within the assault area, which was all the water south of 49° 40' N. latitude lying between the Cherbourg Peninsula and Cap Antifer, he exercised command through the Task Force Commanders. In all the rest of the channel, he exercised command through the C's inC, Home Commands, whom he directed to function generally in accordance with their normal procedure. This accounts for the fact that the Home Commands operated the patrols screening the convoy routes, while the Task Force Commanders operated the patrols screening the assault area.

2 Details of the manner in which ANCXF arranged for the necessary transference of vessels after the assault while leaving the Task Force Commanders a free hand in continuing the area screen for their own area will be found in ON 9 and more especially on ON I, Appendix 11, sections A and B.



B. Eastern Task Force

29. Naval Commander Eastern Task Force delegated control of naval forces screening his area to an authority known as "Captain (Patrols)"1 During the assault phase, this authority was stationed in the ETF flagship. Later he exercised control from R.N. headquarters on the Far Shore. In both cases, he was provided with full details of the position and movement of all objects in the channel, from the radar facilities of C in C Portsmouth, NCWTF and his own ship and shore radar.

30. The system of defense employed in the eastern area was the following:

a. constant patrols to seaward by corvettes, trawlers and sometimes destroyers were carried out;
b. every 24 hours one Division of four destroyers was detailed as duty division for the entire area while two other destroyers were detailed as guard for areas G and J. By day, these destroyers performed such other tasks as were assigned, but they were subject to call in case an attack threatened. By night they were posted as directed by Captain (Patrols). In neither case did they actively patrol up and down the defense line. The plan was that Captain Patrols would vector them against enemy forces, whose presence was discovered by radar or other means;
c. During the hours of darkness or low visibility, this defense was augmented by a line of minesweepers anchored 5 cables apart along a defense line parallel to the shore and six miles to seaward;
d. This defense line was continued down the eastern flank by a line called the TROUT line, composed of LCG's and LCF's, anchored 1 cable apart. The duty of the minesweepers and Landing Craft on this defense line was to prevent all enemy ships and craft from entering the British Assault Area, to illuminate the outer areas when ordered and to counter attack any submarine detected;


1 The elaborate orders which NCETF promulgated for the defense of the British Assault Area, are contained in his British Assault Area Defense Orders (short title BAADO) dated 30 April 1944 and numbered ETF 859/4. The resume given here is very broad.


e. Two or three divisions of MTB's were stationed, stopped but under way, to the North eastward of the N.E. portion of the defense line;
f. Two or three sub-divisions of destroyers were stationed on patrol, to the north of the western half of the area, and sometimes to the northward of the MTB's;
g. Other light forces were stationed close inside the defense line, to act as reinforcements or as "pouncers". B.Y.M.S. and M.M.S. were anchored as minespotters, originally in the approach channels, but later in the lateral swept channel established within the area;
h. These defenses were augmented by a smoke screen laid by specially fitted craft at dawn, dusk, and as required.

31. The enemy's day activity was limited to one long range torpedo attack, by torpedo boats from LE HAVRE, at 0450 on D-day. This attack caused the loss of the Norwegian destroyer Svenner. The attack was assisted by the smoke screen laid by Allied aircraft to cover the eastern flank of the assault from batteries in the Le Havre and Villerville areas. The enemy vessels, were however, engaged, and one torpedo boat was hit by Warspite with 15-in salvoes and was considered sunk.1

32. By night the enemy's attack was more determined. On four occasions he operated torpedo boats, and on eight occasions E and R-boats, in the eastern Task Force area. On every occasion except one, these forces were intercepted and forced to retire. In no case was any success obtained by the enemy. The line L.C.G. and L.C.F., anchored on the eastern flank, took a heavy toll of the human torpedoes which attacked in July. Two enemy torpedo boats were also damaged, five E/R boats sunk, and E/R boat probably sunk, three E/R boats badly damaged, four E/R boats damaged. E.T.F. casualties were two boats damaged with three killed and ten wounded.


1 According to the account of the German Naval CinC West, Admiral Krancke, the attack was carried out by the 5th German Torpedo Boat Flotilla, 15 torpedoes in all being fired. Only minor damage was sustained by the Torpedo boats; but the 15th Patrol Flotilla, stationed off Le Havre "ran into heavy enemy fire" under which one vessel sank, after striking a mine.


C. Western Task Force

33. Naval Commander Western Task Force delegated command and responsibility for the area screen to CTG 122.4. Commander Area Screen (Captain Saunders in the U.S.S. Frankford). The forces employed were:

a. Destroyer Squadrons 17 and 18,1
b. 18 P.C.'s,
c. 6 British Steam Gun Boats,
d. 33 U.S. P.T.'s.

34. The system of defense employed was as follows:

a. The W.T.F. sector was sub-divided into areas with code names (indicated on sketch); an inner screen, about the anchorages, was formed in Areas Oregon and Ohio by Force O, and in areas Kansas and Vermont by Force U; as required to defend their own forces from landward attack by pilotless explosive motor boats, human torpedoes, etc; or as required for protection against attacks by U-boats which might have pierced the outer area screen, or as required for spotting air laid mines.2
b. Initially the picket line, composed of destroyers.3 P.C.s, and S.G.B.s, was formed along the DIXIE Line (see sketch), and connected at its eastern end with the outer defense line of the Eastern Task Force. The pickets were supported by destroyers, in pairs or in company with P.T.s and M.T.B.s; along the MASON Line there were counter-attack divisions of P.T. boats. To avoid being confused with enemy craft all P.T.s, M.T.B.s and S.G.B.s remained in assigned stations at low speed except when enemy contact developed. They were continuously plotted by radar and coached into position by designated destroyers.


1 Destroyers were employed in screening and bombarding duties in rotation.

2 C.T.F. 122 Op. Plan 2 - 44.

3 Guard destroyers were assigned as convenient from reserve fire support destroyers of the assault forces.



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35. The first enemy attempts to enter the assault area were made by E-boats or German coastal craft, during the hours of darkness, by approaching close inshore down the Cherbourg Peninsula. These craft were picked up on radar by destroyers in the picket line at ranges of 10 to 12 thousand yards and taken under fire. The enemy always approached at low speed, sometimes stopping when illuminated, but always withdrew in the face of destroyer gunfire. The screen was never penetrated but it is probable that the enemy laid mines on these sorties.

36. On the night of D plus 3, enemy craft endeavoured to pierce the Screen from approach positions north of the DIXIE Line. These attempts were repulsed. Subsequently, in order to cut off E-Boats which were passing near Pointe de Barfleur, two attack units of S.G.B.s and P.T.s were stationed in MOUNTAIN AREA and were vectored into positions for counter attack by destroyer radar. Although these units made no known kills of enemy E-Boats, their presence and aggressive attitude are considered partly responsible for the fact that no serious threat was made against the Screen.

37. Shortly after the assault, convoys and miscellaneous ships often arrived at the assault area during darkness without previous notice. It was difficult for pickets to recognize these ships as friendly and in one instance, on 13 June, the British cable layer Murdaugh Monach was fired upon by U.S.S. Plunkett. In addition to their screening functions the pickets assisted in reporting mines laid by aircraft, in extinguishing floating flares dropped by aircraft, and in the warning they gave of impending air attacks.


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D. Convoy Escort Forces

38. Every convoy was provided with a group of escorting vessels to protect assault and build-up forces from enemy air attacks and such enemy naval vessels as may have penetrated through the layers of defense above described. The principal problem was that of phasing the allocation of escorts so that the ships involved could be used for other tasks as well. Assault convoys were to be escorted mainly by vessels, which would perform bombardment, area screening, boat control and other duties, when they reached the assault area. A few escort groups were "loaned" to the assault forces by the C's in C, Home Commands. These, together with bombarding ships which had spent their ammunition, were used to escort early convoys returning from the assault area. The "loaned" escort groups were then "returned" to the Home Commands and applied to the build-up escort program.

39. A proportion of the escort vessels, initially assigned the assault forces for the assault phase were later transferred to C in C Portsmouth for the Build-Up phase.1 In addition to vessels engaged in escort work during the assault, some 50 escort groups, with an average of six vessels per group, were engaged in the escort of build-up convoys. These escorts were of miscellaneous types, including escort destroyers, corvettes, motor launches and others. They were required to escort some 32 convoys and groups per day, which was the average number at sea throughout the Build-up.2

40. During the assault, command of escorts were exercised by the appropriate task force, assault force and group commanders. During the Build-up it was exercised by the Home Command through whose waters the convoy was passing. Each escort group was assigned a base port, and authorities responsible for north-bound sailings, assured, so far as possible, that escorts were assigned to north-bound convoys which were proceeding to their home ports. The convoys suffered no losses from enemy action during the assault phase.


1 For allocations of escorts see ON 1 Appendix II, Section A and B, ON 13 Appendix III. For instructions to Task and Assault Force Commanders as to transferring escorts to post assault duties see ON 9, Para.16.

2 See ON 13, Appx. III.



A. Plans For Sweeping German Minefields

41. The enemy's most dangerous available weapon, for employment against Allied ships and seaborne forces, was his sea mining. One of the major Allied naval tasks was therefore to protect NEPTUNE forces from enemy minefields. The naval plan was largely based upon the requirement for sweeping Allied forces through the mine barrier. Under the routing plan the Allied armada were to sortie, from numerous ports along the south-west, south and south-east ports of England, were then to converge on Area Z, proceeding along the British Coastal Channel, and were finally to turn southward, crossing the channel through the SPOUT, in order to approach the assault area. The minesweeping problem was to assure that those routes, the assault area anchorages, and the manoevouring space were free of enemy mines.

42. The enemy mine situation within these NEPTUNE waters, was as follows:

a. Harbour entrances, (through which NEPTUNE forces would sortie after their final assembly) the British coastal channel, along which they would pass to the converging area (Area Z), and Area Z itself, were maintained in a mine-free condition by normal mine sweeping searches executed by Home Commands;
b. There was, however, the possibility that the enemy, once he learned that the Allies were assembling in mass, would lay mines from the air in these waters;
c. To the southward of Area Z the waters were unswept, but searches had indicated that no enemy mines had been laid north of 50° N latitude;
d. The enemy was known to have laid a mine barrier across the northern limits of the Bay of the Seine;1


1 This barrier was thought to extend northward from latitude 50° N to a line, running 092° and 328° from a position 49°27' .5 N and 0° 54' W. See ON 6 para. 5.)


e. Southward of this barrier, the enemy maintained a coastal shipping channel of his own, which could be expected to be free of enemy mines;
f. There was no evidence of mines, inshore of the German coastal channel, but intelligence was incomplete and there might be unknown minefields;
g. There was no evidence of ground mines laid in the shallow water along the beach, but it was possible that there might be some, and it was also probable that, after the assault began, the enemy would lay more;
h. The enemy had available quantity of aircraft with which he could lay mines after the assault was under way.1

43. The general plan for dealing with mines, in NEPTUNE waters, involved five steps:

a. The sortie and convoy routes, Area Z, and that part of the SPOUT lying north of the German mine barrier, were to be regularly searched up until D-1 and after D plus 2, but not immediately preceding the movement of the assaulting forces.2
b. Ten channels, two for each assault force, were to be cut through the mine barrier.


1 The exact number was uncertain because the enemy could easily employ craft for this purpose which were normally bombers.

2 ON 6, Para. 16. During the assault phase all available sweepers would be engaged with the mine barrier or inside the assault area. The risk was not great as the British coastal channel was normally constantly searched, the area north of the barrier was not believed to have mines in it, and it was searched during the weeks before NEPTUNE just to make sure.



c. Transport areas, anchorages, and manoevouring space for bombarding ships were to be searched and swept;
d. The danger of ground mines in inshore waters was to be disregarded during the assault, but the areas were to be searched as soon as sweepers were available;1 thereafter sweepers were to stand by to sweep any ground mines the enemy might lay after the assault started.
e. Channels were to be widened into one broad passage as soon as possible.

44. In view of this plan, and of the disposition of enemy mines, responsibIlity for all searching in and south of the "barrier", and for sweeping force Us lateral passage up to the barrier, was undertaken by the expeditionary forces. Responsibility for searching and sweeping, in NEPTUNE sortie and coastal channels, in Area Z and in the waters of the SPOUT north of the barrier, was left in the hands of the appropriate Cs in C Home Commands.2

B. Minesweeping Arrangements in the Assault Area

45. All minesweeping, in and south of the German mine barrier was undertaken by the Naval Expeditionary Forces. Responsibilities were divided as follows:

a. ANCXF retained direct control of the initial ten approach channels through the mine barrier, for searching and sweeping the transport areas, and for subsequent widening the approach channel, by sweeping out areas between the initial channels;
b. Task Force Commanders arranged for searching or sweeping anchorages, inshore mines, manoevouring space for bombarding ships, and mines laid in the assault area after the assault;


1 Because (a) there was insufficient sweepers to search them, (b) no mines were thought to exist in these waters anyway, and (c) in any case, ground minesweeping ahead of forces could not give security in view of the period delay mechanism with which the mines mere equipped.

2 ON 6, Para. 16.



c. Each Task Force Commander delegated command of minesweeping in his area to a senior minesweeping officer who was responsible for operation of all minesweepers in each area, and for coordination with the activities of the two Task Forces.1

46. The total strength of Allied minesweepers, engaged in the assault,2 was 255 vessels. This force comprised:

a. twelve fleet minesweeping flotillas of 9 ships per flotilla;3
b. six flotillas (of 10 ships each) of YMS type motor mine sweepers;4
c. seven flotillas (of ten ships each) of British type motor mine sweepers;5
d. four groups (of five ships each) of mine sweeping trawlers;6
e. thirty-six R.N. mine sweeping motor launches;
f. forty-eight R.N. danlayers; and
g. nine miscellaneous supporting ships and craft.7


1 ANCXF Report, Appx. 14.

2 Operations in and south of the German mine barrier.

3 These were the 1st, 4th, 6th, 7th, 9th, l4th, 15th, 16th, 18th, 31st and 40th R.N. minesweeping flotillas and the 7th U.S.N. minesweeping squadron.

4 Four flotillas, the 150th, 159th, 165th, and 167th M.S.F. were British and two Y-1 and Y-2 were American.

5 The 101st, 102nd, 104th, 115th, 132nd, 143rd, and 205th R.N. MMS flotillas.

6 The 131st, 139th, 159th and 181st R.N. Groups of "LL" trawlers.

7 For details of ships and craft taking part in the minesweeping operation and their organization see ON 6, Appx. II.



47. Provision of such a large number of minesweepers severely taxed Admiralty's resources. To meet the requirement, minesweepers had to be withdrawn from other important services. When the scale of the Assault was increased from a three to a five-division basis, requiring four additional channels to be cut for the two new assault forces, it was necessary to allocate four additional flotillas. One was a new flotilla, not commissioned until the eve of the operation; one was an ancient flotilla from the 1st World War; one was a decimated flotilla from the Mediterranean; and one a Canadian flotilla which had spent its entire career in escort duty.

C. The Passage and False Start

48. The passage was technically defined as starting, when a vessel left the searched channels of the English coast and as ending, when it entered the swept channels of the mine barrier. The passage of all assault forces, except certain convoys of Force U, was through the SPOUT. The Assault Forces were not "swept" through this passage,2 as it was too short to enable minesweepers to precede the Assault Forces and still enter the barrier on time, as other minesweepers were not available for the job, and in view of the fact that no mines were known to have been laid in the area, as C in C Portsmouth had searched the SPOUT at the last possible moment.

49. The route of Force U, from the West Country to the entrance of approach channels 1 and 2, lay through an unexplored area. Force U convoys sailed on 3rd June. Early on the 4th, the 14th and 16th Minesweeping flotillas sent sweeps to explore the route ahead of them. The 16th Minesweeping flotilla received the postponement signal, at 0840 on the 4th June, and turned back. The 14th Flotilla, which was further ahead, had not yet received the signal when they found mines. The senior officer detached a PT boat to report the minefield, but, the weather rapidly deteriorating, extricated his flotilla and turned to the westward.


1 ON 6, Para. 26.

2 ON 6, Para. 29.



50. ANCXF considered that these mines were a chance lay, jettisoned by E-boats, and decided not to attempt to change the route of Force U. The following day, when the operation was resumed, the 14th Minesweeping Flotilla swept and buoyed a channel through the minefield, cutting one more mine. A PT boat was detailed to shepherd the following convoys through this channel. Further on, the 16th minesweeping Flotilla cut four more mines along this route. Force U passed safely through this minefield, but it claimed the first casualty of the operation, U.S.S. Osprey.1

D. The Approach

51. The Approach was technically defined as beginning, when the loading minesweepers of each Force began cutting through the barrier, and as ending, so far as minesweepers were concerned, when they had reached and swept the transport area.2 Two channels were cut through the mine barrier for each assault force in order to assure the safe approach of the five Assault Forces. Each channel varied from 400 to 1200 yards in width. Each Assault Force was also provided with one "transport area" of searched waters, 4 to 6 miles long and some 2 miles wide, situated in the mine free German coastal convoy channel.

52. Ten flotillas of fleet minesweepers were detailed to cut the 10 channels and to search the five "transport areas". Each flotilla consisted of nine fleet minesweepers, to which was attached four minesweeping motor launches, two Oropesa minesweeping "LL" trawlers, and four danlayers. The motor launches, equipped with light sweeping gear, preceded the leading fleet sweeps in order to clear a path for them. The "LL" trawlers swept for magnetic mines while the danlayers buoyed the channel, to guide the oncoming Assault Forces.


1 ON 6, Para. 28. ANCXF Report Appx. 14.

2 ON 6, Paragraph 27.

3 ON 17. Appx. II.

4 see ON 6, Appx. I, and ANCXF Report Vol. I, Appx. 14.



53. In order to assure that the channels cut would be located in the proper positions, 10 - sonic underwater buoys were laid in positions to mark the edge of the enemy mine barrier in the Assault approach channels.1 These Buoys were laid so as to come alive on D minus 1, when they would be utilized by H.D.M.L's, acting as marker boats, to enable the mine sweepers to commence sweeping the approach channels in the correct positions. Once sweeping was begun from the correct starting points, accuracy of navigation was aided by the use of QH and QM electronic navigational devices and by taut wire. The course of all the channels cuts were within 100 yards of their intended positions.

54. To prevent the enemy from learning of the Allied approach, or of the area at which the Assault was aimed, until the last possible moment, it was essential that barrier cutting minesweepers should not operate too far in the van of the leading assault ships. The maximum speed of the leading craft in some channels was 5 knots the minimum safe minesweeping speed was 7½ knots. The minesweepers were therefore required to lose approximately an hour and a half. They accomplished this by back-tracking for 40 minutes just before they came within range of enemy radar. Making two 180° turns with sweeps streamed was a difficult manoeuver, further complicated by the tide. Before the appearance of German beach obstacles, H-hour was scheduled to be 3 to 4 hours before high water. On that basis the cutting of the barrier would have begun, on a weak east-going, and finished on a strong west-going, tidal stream. This would have permitted the whole sweep to be carried out in a "G" formation to starboard. The wasting of time could have been accomplished by turning 180 degrees in succession, back into the swept channels. But because of the beach obstacles, H-hour was set at an hour or so after low tide. The sweep, therefore, started with a strong east-going stream, which, in the later stages, turned to a strong west-going stream.

55. It therefore became necessary to begin the operation in "G" formation to port and to change sweeps at the change of the tide. A method of doing this, while wasting time, was devised and adopted with minor variations by the majority of flotillas. All ships, except the leader, recovered sweeps in succession from the rear and formed line ahead, protected by the leader's sweep. On completion, ships successively turned 180 degrees, staring with the rear ship, and retired along the channel already swept. After all ships had turned, the leader recovered her sweep, turned


1 Op ENTHRONE. See ANCXF Report Vol. 1, Page 42.


and followed the others. When sufficient time had been lost, the flotilla turned 180 degrees together, streamed starboard sweeps and, reaching the last danbuoy, formed "G" formation to starboard. This was successfully tried out in practice by some of the flotillas. Most of them were unable to exercise the new manoeuvre, as they had been employed during the last fortnight in clearing minefields laid by the enemy in his pre-invasion offensive, and in searching prospective NEPTUNE convoy lanes.

56. This manoeuvre was successfully carried out by all flotillas, even though the 9th and 18th had to execute it in the middle of a minefield. The 6th flotilla was unable to lose as much time as planned because the leading landing craft in channel 5 were ahead of program. The latter part of this flotilla's sweep, therefore, had to be carried out at a speed of about 6 knots, but no mines were found in this channel. The enemy were not alerted by the approaching sweepers, although the 14th minesweeping flotilla, which was operating the lateral convoy route of Force U, and in the first approach channel, was in sight of the French coast from the afternoon of D minus 1.1

57. During the passage and approach, the weather was heavy. This caused little trouble to the fleet minesweepers, but it made sweeping very difficult for the motor launches, which were, however, able to carry out their task. ML's cut two mines from the path of the leading fleet sweep of the 9th minesweeping flotilla. The danlayers also had trouble with the weather. Some dan lights were smashed in launching, but the reserve danlayers filled the gaps. All channels were adequately marked and the Assault Forces found them easy to follow. Sweep cutters were met in Channel 5, but no mines were found. 29 mines were cut in Channels 2, 6 and 7. Throughout the approach, the leading minesweepers checked their positions by QM, QH, and taut wire measuring gear. In two cases one or the other method failed, but all flotillas succeeded in laying their terminal dans within a cable of the assigned positions and within a few minutes of the planned time. The five transport areas were searched on schedule, but no mines were found.


1 As will be seen in Chapter VIII, Section 8, this flotilla was screened from radar detection by Allied Radar counter measures.


58.3 Immediately the sweeping of the approach channels and transport areas was completed, the twelve flotillas of fleet minesweepers turned to three other urgent tasks:

a. searching waters required for the movement of bombarding ships;1
b. clearing lateral channels connecting the inshore terminals of the ten approach channels; and
c. widening the approach channels.

These three tasks were executed concurrently. Three fleet minesweeping flotillas were detailed to the Task force Commanders for bombardment minesweeping, three for sweeping connecting channels, and two to standby for special requirements. The remaining four, operating under the direct control of ANCXF, immediately began sweeping out the areas in the German mine barrier lying between the approach channels. They were joined by the other flotillas carrying out this task, when the search of bombardment and lateral areas was completed.

59. The intricate manoeuvres necessary to disengage ten flotillas in a confined space were successfully accomplished. In conducting the search of the bombarding areas some flotillas operated within two miles of the enemy shore. In this phase there was some mutual interference between minesweepers. Some of the searches planned were not completed before oncoming landing craft forced the minesweepers out of the way. These searches, however, revealed that the inshore areas were clear of moored mines. The ten narrow channels through the German mine barrier were inadequate to accommodate the requirements of the enormous post-assault cross-channel shipping program. When the fleet minesweepers had completed their assault tasks, they were therefore employed in clearing the entire barrier between the first and the last approach channels. In so doing, they concentrated on merging two pairs of adjacent approach channels to make them available by the end of D-day, and their rejoinder with other minesweeping flotillas.


1 In order to safeguard the bombarding battleships, cruisers, destroyers, and other ships which would be required to move around in the congested assault area, often very close to the shore, it was considered essential that their movements should be preceded by minesweeping. Bombardment was to begin before H-hour so that no time could be wasted between the completion of sweeping the approach channels and transport areas and the beginning of sweeping for bombardment forces. The areas which were swept are defined in ON 6, Appx. I. For diagrams see ANCXF Report Vol I,Appx.l4 and ANCXF Report Vol. III,Annex H.


60. The clearance of the space between channels 3 and 4 (known as channel 34) and between 5 and 6 (channel 56) was completed according to plan on D-day; Channels 12 and 78 were completed on D plus 1; Channel 14 was finished on a D plus 7; and channel 58 was cleared to a width of six miles by D plus 8. The entire barrier within the SPOUT was open by D plus 12. The clearance of the enemy mine barrier was carried far enough to the north to ensure that the whole of the minefields discovered during the approach was cleared. 78 moored mines were found in this field alone.

E. Sweeping Inshore Waters

61. Inshore waters, lying between the transport area and the assault beaches, were not swept during the initial assaults. The risk of loss from mines in these waters was accepted because:

a. it was not thought that the Germans had laid any mines in inshore waters;
b. the project would have demanded more sweepers than were available;
c. the delay which would have been required between the cutting of the barrier and the assault was unacceptable; and,
d. minesweeping could offer little protection in any case, in view of the period delay mechanism with which enemy moored mines were equipped.

62. Inshore areas, especially the boat lanes between the transport areas and the beach, and the areas of the artificial harbors were to be swept as soon after the assault as possible. For this purpose, each assault force was allocated one flotilla of YMS or BYMS, one flotilla of British Motor Minesweepers, and a group of 6 minesweeping LCT's. All three types of vessels were equipped with light sweeping gear especially designed for sweeping moored ground mines in shallow waters.1 Inshore waters were searched shortly after the first assault. But no mines were found until after the enemy began laying them from the air.


1 See ANCXF Report, Vol. III, p. 63. It was originally planned to use also LCV(P)s equipped with very light gear for work very close to shore, but in trials it was found that the gear broke up before the craft could reach the shallow water.


F. The Enemy's Minelaying Counterattack

63. It had been anticipated that the enemy, after the assault, would counter attack strongly by laying mines in the assault and Build-up channels. This appreciation proved correct. In the first month after the assault, the laying of ground mines by aircraft by night was the enemy's chief weapon for impeding the Allied Build-up. This mine-laying forced the Allies to take risks, which had previously been considered unacceptable, inflicted casualties, and slowed up shipping movements. The effect on the Build-up was however negligible.

64. The first indication of the extent of the ground mine problem came on D plus 1, when some 30 ground mines were detonated in the neighbourhood of the CARDONNET shoal in the UTAH area. It is uncertain whether this field was in place before the assault, with period delay mechanisms which prevented its discovery on D-day, or whether surface craft succeeded in laying it on the night of D-day. The field claimed seven casualties including two U.S. destroyers, the Glennon and the Meredith, the U.S. Destroyer Escort Rich, and the U.S. Fleet minesweeper Tide. In the eastern area also the air mining effort mounted steadily. It soon became apparent that the sweepers were not keeping pace with mines dropped in the channels and anchorages. Fifteen casualties, three vessels sunk and twelve damaged, were suffered in the ETF area by D-plus 16, while some ninety mines had been swept.

65. On 20 June it was discovered that the Germans had been using a new and secret type of mine (the pressure mine), which was unsweepable by existing Allied methods.1 To counter this danger, a series of measures were taken which were effective in reducing sharply in casualty rate, then confined mainly to near misses on sweepers. The following were the steps taken:

a. Airfields, from which enemy minelaying aircraft were operated, where heavily and repeatedly bombed;


1 This was a pressure acoustic mine which depended for actuation on both the increased water pressure caused by a ship passing in its immediate vicinity and the sound of the ship. Another variation was the pressure magnetic mine.


b. Allied night fighter aircraft cover was increased and special attention was given to the intercepting of minelayers;
c. the width of ship channels was reduced, while all available minesweepers were concentrated on these narrower waters;
d. to reduce pressure caused by the movement of ships, speed restrictions were imposed on all vessels operating in mined waters;
e. when it was necessary to move heavy ships in such shallow water that their speed could not be reduced to a safe figure, tugs were employed with a long tow, in order to avoid pressure and acoustic actuations being applied simultaneously;
f. when it was discovered that a swell would reproduce the pressure conditions required to fire an acoustic "oyster" mine and that lower speed would then be no protection all movements were stopped when such conditions existed, until channels had been swept;
g. it was also learned that period delay mechanisms could be worked off without pressure actuation. Sweeping schedules were accordingly adjusted, under swell conditions to cover as large an area as possible of all channels and anchorages.

G. Minesweeping at Cherbourg

66. The early capture and employment of a major port on the Far Shore was essential to OVERLORD. Without it the Allied armies could not be adequately supplied. The Germans, fully realizing this fact, sought to prevent the Allies from capturing Cherbourg and from putting it quickly in workable condition. The German plan to make Cherbourg unworkable included provision for sowing the approaches, channels, anchorages, and berths, with a profusion of mines.


67. NCWTF put Commander M/S West in charge of the operation of clearing mines from Cherbourg. Intelligence data available, as to the extent of mining in and off the harbor, was of great assistance in framing for this difficult clearance.1 Before Cherbourg was taken, during the northward advance of the U.S. Army along the Cotentin Peninsula, channel "L" was extended along the east and north coasts to protect bombarding ships employed in support of the Army's advance. During these operations, the minesweepers 2 repeatedly came under fire of shore batteries. Within 24 hours of the silencing of the last battery, "H" and "L" channels had both been established and an area off the harbor entrance cleared to seaward of the 10-fathom line. The clearance of moored mines, within the 10-fathom line outside the harbor was effected by the two U.S. YMS squadrons, the 167th BYMS, and 206th MMS Flotillas.

68. Inside the harbor, the principle adopted of first clearing as much of the Grande Rade, as was necessary to gain access to the Petite Rade, and enough of the latter to provide a passage to the Avant Port de Commerce and to the Nouvelle Plage. Each lap was first searched for snag lines by LCV(P)s. A passage was then swept by ML's wide enough to start Oropesa clearance with YMS. Ground minesweeping of each lap was started, as soon as it was safe from moored mines. Motor launches and LCV(P)s were used for clearing very confined spaces in which not even a YMS could manoeuvre.


1 Two rows of G.Y. mines with snag lines and 8 ft. of 5/8th inch chain moorings had been laid across the eastern entrance of the GRANDE RADE. The western entrance was similarly blocked with mines with delayed release sinkers. The GRANDE and PETITE RADES shoreward of the wo fathom lines were well fouled with "Katies". There was a line of G.Y. mines across the entrance to the PETITE RADE and both RADES had been well sprinkled with acoustic, magnetic, moored and apparently delayed release moored mines.

2 The 7th USN Minesweeping Squadron and the 9th and 14th RN Minesweeping Flotillas.



69. At the same time, two "P" parties of Commodore Sullivan's port salvage organization, searched Bassin Des Flots, the Avant Port de Commerce and the shallows of the Nouvelle Plage, working outwards to meet the sweepers. To avoid danger to "P" party divers from exploding mines, these parties worked only for three hours either side of low water. The mine-sweepers worked three hours either side of high water. Entry to the landing point, most easily reached, having been made as rapidly as possible, clearance was extended to the docks and basins which had been more thoroughly blocked. Cherbourg port was free of mines and was receiving ships by 19 July.

H. The Score

70. Ships lost to enemy mines, and mines accounted for between 4th June and 3rd July were:

  Western Task
Eastern Task
Casualties 24 19 43
Moored mines swept 91 95 186
Ground mines swept 140 109 249
Ground mines accounted for other than by minesweepers 6 68 74
  261 291 552


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A. Coordination of Coastal Command and Naval Operations

71. Aircraft operated by Coastal Command, R.A.F. effectively assisted in the tasks of defending NEPTUNE. from enemy naval counter action. The tasks of these Coastal Command aircraft were:

a. in conjunction with covering naval forces, to impede the movement of enemy warships, especially U-boats, from their northern bases to the Biscay area;
b. in conjunction with naval covering forces, to prevent enemy vessels, and especially enemy U-boats, from penetrating into the English channel;
c. to assist Allied naval forces in protecting NEPTUNE shipping, convoys, and assault area, from attack by enemy surface vessels and U-boats operating within the channel;
d. to assist naval forces in disrupting enemy sea-borne transport in order to impede the movement of enemy reinforcements and supply into the assault area and in order to make German coastal supply lines difficult and costly.

72. Operational command of coastal Air Forces, operating in support of NEPTUNE, was exercised by the R.N.C.'s Home Commands in conformity with the standard British system


for control of R.A.F. anti-U-boat forces.1 During the early stages of NEPTUNE planning, no special command channels were established for coordinating the operations of Coastal Command with NEPTUNE operations. ANCXF reported his requirements to Admiralty or to the appropriate Home Commands, and relied on them to make the necessary arrangements. This method however proved to be clumsy, especially in connection with tasks in close support of the operation, and was found to be inadequate in providing the required degree of integration. At a later date, Admiralty authorized direct communication between Coastal Command and the various commands of the Naval Expeditionary Force. While this greatly facilitated the making of individual and specific arrangements, no integrated NEPTUNE plan for Coastal Command was developed and operations were executed by more or less improvised methods.2


1 This system was broadly as follows: (a) Coastal Command, whose primary mission was anti-U-boat warfare, was one of the major sub-divisions of the R.A.F., (some other major sub-divisions were Bomber Command, Training Command, Fighter Command, etc.) and was commanded by the Air Chief Marshal, Commander in Chief Coastal Command. For administrative and logistic purposes he was directly under the command of British Chief of Air Staff, but the Chief of Air Staff had assigned operational control of Coastal Command Forces to Admiralty.
(b) The major operational sub-divisions of Coastal Command were GROUPS. Admiralty assigned operational control of groups based in the United Kingdom to appropriate Home Commands.
(c) The C's in C, Home Command, employing a suitable air staff from Coastal Command, and in conjunction with naval forces, then operated assigned groups for air patrol of the waters for which they were responsible.
(d) Supervision and coordination of joint operations was effected by the joint control of Admiralty and C in C Coastal Command. (See Fairwing 7, History, for further details.)

2 ANCXF Report Vol. l, Page 30.



73. The forces engaged in these operations included the U.K. based Aircraft and Coastal Command, six RN Fleet Air Arm Squadrons, and U.S. Navy Fleet-Air-Wing Seven. To provide continuous air patrols in the South Western approaches, number 19 Group, which included the greater part of RN and USN formations of anti-U-boat aircraft, was disposed in the south and southwest under the orders of the C's-in-C, Plymouth and Western Approaches. Some anti-shipping aircraft were made available in this group, in case the enemy attempted to send surface vessels from the Bay of Biscay into the Channel. In the east and southeast, Number 16 Group operated a formidable force of anti-shipping aircraft. Arrangements were made to transfer anti-U-boat squadrons from 19 Group to 16 Group of the enemy sought to operate U-boats in the southern North Sea. Number 18 Group was stationed in the north to counter any movement from northern enemy ports into the Biscay or channel area. A flexible system, of re-inforcing any of these Coastal Command Groups from the resources of the others, was devised to meet any developments which might arise.

74. Coastal Command operations in support of NEPTUNE opened in Norwegian waters on May 16. It had been anticipated that the enemy might try to reinforce his Biscay Flotillas by sending U-boats from the Baltic and Norwegian ports to the Atlantic via the Northern Transit Area. This appreciation proved correct, and to counter these movements, Number 18 Group opened a vigorous and sustained offensive. By the eve of the invasion, this offensive had resulted in 22 sightings, 13 attacks and 6 kills. By 30 June the score was 44 sightings, 28 attacks and 13 probable kills.

75. By the 6th of June, the majority of the enemy's U-boats were assembled in the Biscay area,1 as part of his basic strategic plan, assigning the U-boat a major role in the plan to frustrate the invasion. Their task was to enter the channel and, by getting between the assaulting forces and their British Bases, to prevent the Build-Up. When the Normandy landings began, the U-boats made for the assault area, proceeding on the surface whenever possible in a order to attain the utmost speed.


1 On that date they (the U-boats) were offensively deployed. This fact is another striking indication of the fact that the enemy had been unable to discover the approximate invasion date.


76. Coastal Commands main task was to prevent these U-boats from arriving inside the channel. It planned an air barrier over CORK the entire area of the western approaches to the channel, extending from the shores of Devon and Cornwall to the shores of Brittany, and from the Scilly Isles to the Cherbourg Peninsula. This area was covered with air patrols, which were so timed that every spot in CORK came under observation every thirty minutes.1 As CORK was so wide that U-boats could not pass through it without surfacing, and as the entire surface was under constant surveillance, few, if any, submarines were able to enter the channel undetected. The solid wall of air patrols in the CORK proved effective. On the night of 6/7 June, 11 U-boats were sighted and 6 attacked; in the following 24 hours, 10 more were sighted, 6 attacked, and 3 probably sunk. After thirty days, the score for the operations in the Biscay and Channel areas was 96 U-boats sighted, 59 attacked, 6 certainly sunk, and a great many more probably or possibly sunk.

77. After this initial set back, the U-boats began to try to get through by remaining submerged and by relying on "SCHNORKEL" to ventilate and charge. 2 These tactics effectively restricted their speed and freedom of manoeuvre and had a most distressing effect on their crews. The few U-boats, which did succeed in penetrating the air barrier, arrived in an exhausted condition. During the first two months no losses to the invasion forces were known to have been caused by U-boats.


1 The reason the thirty minute interval was chosen was because a U-boat was believed to use up, in a crash dive approximately as much battery energy as could be charged into the batteries in thirty minutes surface charging.

2 The "SCHNORKEL" was a pipe with two vents which was pushed up from the submarine's interior. This enabled a U-boat, at periscope depth, to expel exhaust gases from its diesel motors and suck in fresh air from above the surface. Submarines employing Schnorkel were hard to detect because the exposed portions were only some 20 inches in diameter and extended only some 6 feet above the water. During the early months of the invasion the enemy had not fully learned how to use it, but later in the summer when they were able to use it at greater depth and with less exposure above the surface, the entire character of the anti-U-boat effort was changed.



78. While the U-boats were being dealt with in the south-west and the north-west, Coastal Command also cooperated with the Navy in actions against enemy surface forces. It was expected that German destroyers and light craft would operate vigorously against Allied convoys. Hence, 16 and 19 groups were strengthened to assist naval forces in warding off this threat. Soon after the invasion began, the enemy tried to reinforce his surface craft in the assault areas by bringing up destroyers from the Gironde. On the 6th of June some of these vessels were attacked by aircraft south of Brest, but the damage inflicted did not prevent the enemy from making port. Two days later, four destroyers tried to round the Brest Peninsula, but were brought to action by the Royal Navy. One destroyer was sunk, one driven ashore and a third was forced back to Brest in a damaged condition. The beached destroyer was later attacked by aircraft and reduced to a total loss. After this, the enemy made no further attempts to reinforce his surface craft from the west.

79. In the early stages of the invasion, the enemy operated channel based light forces, mainly E-boats, on a considerable scale against the assault area. Some 30 of these vessels were based between Boulogne and Cherbourg, but the number was substantially reduced by surface action, including coastal aircraft, and by several heavy bombing attacks against Le Havre and Boulogne. The operations of Coastal Command against these light forces consisted mainly of continuous anti-shipping patrols in the Channel. A great many air attacks, mostly at night, were made in conjunction with naval patrols against E-boats, R-boats, minesweepers, and trawlers. In addition, aircraft carried out considerable reconnaissance work, dropping flares and directing naval forces to their targets.

80. Coastal Command also contributed to the successful Allied effort to disrupt the enemy's coastwise transport. On 15 June, north of Schiermonnikoog, a merchantman of 8,000 tons and a naval auxiliary of 4,000 tons were sunk and three minesweepers of the escort damaged. On 29 June a 1,000 ton tanker and one of its escorting minesweepers was attacked and damaged; on 20 June two "M" class minesweepers, one armed trawler, and an auxiliary were badly hit off Concarneau. Apart from the losses suffered, the enemy was obliged to divert, to purely defensive tasks, numbers of minesweepers and naval escort craft urgently required elsewhere.


81. Bomber missions also contributed to the protection of seaborne NEPTUNE forces from enemy naval action.1 The employment of bombers in mine-laying has been described already.2 On the evening of 14 June, 353 heavy bombers attacked Le Havre with 1026 tons of bombs, including twenty-two 6-tonners, destroying, among other things, over 25 enemy naval vessels. On the 15th June, 297 heavy bombers attacked Boulogne, concentrating on U-boat pens.3

B. Air Defense by Combined Allied Air Forces

82. The defense of NEPTUNE from enemy air attack was a major task. Some 1,515 enemy aircraft were available for use against NEPTUNE, including 340 heavy bombers, 75 reconnaissance bombers, 75 fighter-bombers, 560 twin-engine fighters, 390 single-engine fighters, and 75 coastal aircraft. These planes were so disposed that some 185 aircraft were in the Normandy area, 360 in the Pas de Calais area, 135 in Holland, 375 in north-western Germany, and 100 in Scandinavia. The Germans were not considered to be able to deploy more than this against NEPTUNE, as their remaining air resources were required on their eastern and southern fronts.


1 Questions relating to the integration of Naval and Bomber operations are dealt with in Chapter VIII which deals generally with Bombardment and Air Bombing in their role of defense against enemy shore action and offensive assistance to the army.

2 See Section 2, of this Chapter.

3 These were berths for U-boats covered over by reinforced concrete.



83. Allied air forces, available for defense against hostile aircraft, consisted of the 9th U.S. Air Force, and the British Second Tactical Air Force. Taken together these comprised some 2,300 aircraft.1 Allied fighter cover was employed in the following manner:-

a. Five squadrons of sixteen planes each maintained a constant patrol over the convoy lanes, with five additional squadrons on call if required.
b. Ten squadrons, of sixteen planes each, maintained a constant patrol over the assault beaches, with a reserve of ten squadrons on call at all times.
c. Some eight squadrons of light and medium bombers were available as required to bomb the enemy airfields from which attacks were launched.

84. Until air fields could be constructed on the Far Shore, the problem of maintaining fighter patrols over beaches and convoy lanes taxed the endurance of fighter craft. The distance to and from airfields in England was so great, that each plane was able to patrol for only 20 minutes over the beaches. A large proportion of the air cover effort was thus absorbed in simply going and coming.

85. The command and control of NEPTUNE air forces was not delegated to the lower echelons of command, as was the policy with Army and Naval forces. It remained, on the contrary, in the hands of the very highest echelon, AEAF. The air operation was in fact one continuous battle and not a series of local engagements. In order to keep all Allied air defense resources available to meet any enemy threat, air forces could not be tied down to a series of local tasks, but had to be free to move about over the entire area, as the enemy reaction required.

86. The single authority, exercising control over all NEPTUNE fighter defense aircraft, the "Advanced Headquarters AEAF", was located at Uxbridge, near London. This "Advanced Headquarters" was kept informed of the movements of enemy aircraft in the entire Western European area, by reconnaissance, radar, and other resources. All such information was fed into Uxbridge and air deployments were made accordingly.


1 This figure does not include Allied Bomber Forces, nor does it include fighters employed in the support of Bombers. Bombers, however, contributed effectively to the defense of NEPTUNE against enemy hostile aircraft by executing several attacks on enemy airfields from which hostile aircraft were flown.


The fields from which the aircraft operated were scattered all over southern England. This system of remote control was obviously unable to direct effectively local movements of aircraft in the assault area. This was assured from three fighter direction tenders. These were naval landing ships (LST's) equipped with all the radio and radar gear required for the tactical control of aircraft. An elaborate operations room was installed in which the movements of all aircraft, friendly or hostile was plotted. Intelligence of the local situation was provided by local radar and reconnaissance. Intelligence of more distant air movements was supplied by radio from Uxbridge. The navy operated the vessels, while airforce commands operated the fighter control.

87. Under this system of local control, planes on patrol, and also reserve planes sent specially as reinforcements, were despatched by the control authority at Uxbridge. On arrival each plane made radio contact with the air operation room of the fighter direction tender. While the plane remained in the area, the FDT vectored it to its target, and generally directed its movements. When its tour was completed, usually because its gasoline was exhausted, control of the plane was returned to Uxbridge. Three FDT were employed for the operation, one stationed in the WTF area, one in the ETF area, and one in mid-channel. Fighter Direction Operation rooms, complete with radar and radio equipment were installed on three other ships, which were stand-bys in case the FDT's were sunk.

88. The Air Force Command intended to transfer local control of fighter aircraft from the FDT's to the French Shore on D plus 1. To do so they landed several Ground Control Intercept (GCI) parties on D-day. These were, however, badly mauled in landing and were unable to function until after D plus 6. In order to enable individual ships to call for help against hostile aircraft, and to provide for relaying information of movements of hostile aircraft, a special radio channel was provided. Calls for help were received at Uxbridge and on the FDT's, one or the other of which took appropriate action. The Joint Force Broadcast a general purpose radio circuit, to which nearly every vessel was tuned, was used for air warnings, to keep ships and craft warned of movements of hostile and friendly planes.


87. The anti-aircraft armament of all vessels was available for use against hostile aircraft, while each Commanding Officer was responsible for using it for the protection of his own ship. The main problem, however, was that of keeping ships from shooting down friendly aircraft, and of coordinating the use of anti-aircraft guns with movements of air covering forces. In order to drive enemy planes by anti-aircraft fire up to an altitude where the Allied fighters could deal with them, and then to stop AA fire, so that these friendly planes could do their job, a plan was tried which provided that ships should fire their AA only on a signal, and should cease fire on a signal. This plan however, did not work, as the gunners on many ships did not obey the signals. At a later date, the plan was tried again in captured ports with some success.

88. The enemy's air reaction to NEPTUNE was unexpectedly small. Most of his fighters were used in a defensive role against Allied bombers. The first sortie against NEPTUNE shipping came at about 3 o'clock on D-day, some fifteen hours after the first arrival in the assault area. During the following night some eight-five aircraft, mostly mine layers, flew over the beaches and shipping lanes. On D plus 1, some fifty-nine enemy aircraft were in the battle area of which fifteen were destroyed. Thereafter the enemy's reaction dwindled gradually. By the middle of July, air attacks on the NEPTUNE area had virtually ceased.


[End of Chapter 7]

Published: Mon Mar 16 08:24:29 EDT 2015