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This extract is one of the most comprehensive accounts of the
minesweeping operations that took place on D Day.
Source:
http://www.ibiblio.org/hyperwar/USN/rep/Normandy/ComNavEu/ComNavEu-433.html
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Source:
Historical Section, COMNAVEU. "Administrative History of U.S.
Naval Forces in Europe, 1940-1946." vol. 5. (London, 1946):
301-337 [This manuscript, identified as United States Naval
Administrative History of World War II #147-E, is located
in the
Navy Department Library's
Rare Book Room.]
Transcribed and
formatted by Charles Hall for the HyperWar Foundation
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PART V
'NEPTUNE'
MINESWEEPING OPERATIONS
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 manoeuvring 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
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.2
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.3
b. Ten channels, two for each assault force, were to be cut
through the mine barrier.
c.
Transport areas,
anchorages, and manoeuvring 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;4
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.
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, manoeuvring space for bombarding ships, and mines laid in the
assault area after the assault;
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.5
46. The total strength of Allied minesweepers,
engaged in the assault,6
was 255 vessels. This force comprised:
d.
twelve fleet minesweeping flotillas of 9 ships
per flotilla;7
e.
six flotillas (of 10 ships each) of YMS type
motor mine sweepers;8
f.
seven flotillas (of ten ships each) of British
type motor mine sweepers;9
g.
four groups (of five ships each) of mine
sweeping trawlers;10
h.
thirty-six R.N.
mine sweeping motor launches;
i.
forty-eight R.N. danlayers; and
j.
nine miscellaneous supporting ships and craft.11
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, 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 end 16th Minesweeping flotilla
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.
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.
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. 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.
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. 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 minesweepers 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 manoeuvre, 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 tuning 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 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 1.12
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 ware 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.
58.
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;13
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 end 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.
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 the 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 then 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 harbours 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.14
Inshore waters were searched shortly after the first assault. But no
mines were found until after the enemy began laying them from the
air.
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 l6, while some ninety mines had been swept.
65.
On 24 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.15
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;
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 can 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 harbour, was of
great assistance in framing for this difficult clearance.16
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
17
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 harbour entrance cleared to
seaward of the 10-fathom line. The clearance of moored mines, within
the 10-fathom line outside the harbour was effected by the two U.S.
YMS squadrons, the 167th BYMS, and 206th MMS Flotillas.
68.
Inside the
harbour, 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.
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 29 July.
H. The
Score
70.
Ships lost to
enemy mines, and mines accounted for between 4th June and 3rd July
were:
|
|
Western Task
Force |
Eastern Task
Force |
Total |
|
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 |
Footnotes:
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.)
2
The exact number was uncertain because the enemy could easily
employ craft for this purpose which were normally bombers.
3
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 at barrier was not
believed to have mines in it, and it was searched during the
weeks before NEPTUNE just to make sure.
4
Because (a) there were 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.
5
ANCXF Report, Appx.14.
6
Operations in and south of the German mine barrier.
7
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.
8
Four flotillas, the 150th, 159th, 165th, and 167th M.S.F. were
British and two Y-1 and Y-2 were American.
9
The 101st, 102nd, 104th, 115th, 132nd, 143rd, and 205th R.N. MMS
flotillas.
10
The 131st, 139th, 159th 181st R.N. Groups of "LL" trawlers.
11
For details of ships and craft taking part in the minesweeping
operation and their organization see ON 6, Appx.II.
12
As will be seen in Chapter VIII, Section 8, this flotilla was
screened from radar detection by Allied Radar counter measures.
13
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.
14
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.
15
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.
16
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 ten 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.
17
The 7th USN Minesweeping Squadron and the 9th and 14th RN
Minesweeping Flotillas.
PART IV
ASSAULT AREA: SCREEN AND ESCORTS
A.
Allied Naval Dispositions.
ANCXF assigned to the appropriate Task Force Commander the task of
screening the assault area against enemy naval penetration. 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.
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 C in C Portsmouth for escort duty
to facilitate his task of operating the post assault build-up convoy
program.2
B.
Eastern Task Force.
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.
The system of defence 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 O 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 defence 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 defence was
augmented by a line of minesweepers anchored 5 cables apart along a
defence line parallel to the shore and six miles to seaward;
d. this defence 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
defence 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;
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 defence 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 defence 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 defences were augmented by a smoke screen laid by specially
fitted craft at dawn, dusk, and as required.
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-inch
salvoes and was considered sunk.
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 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.
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