This subject has not been covered very extensively in published
work since 1945 although it is thoroughly recorded in the Naval Staff History
"BRITISH MINING OPERATIONS 1939 - 45" and receives some attention in
WAR AT SEA by S. W. Roskill. Since access to the
Naval Staff History is limited it is hoped the following outline will provide
wider recognition of the very successful work carried out by Light Coastal
Three types of minelaying were carried out by RN surface craft
and submarines during WW2. Defensive minefields to act as barriers, such as
those laid in the North Atlantic,
Anti-submarine Traps at focal points for convoys, and Offensive mining to
disrupt movement of enemy shipping in coastal waters. Only Offensive mining
operations were carried out by Motor Launches, Motor Torpedo Boats and Motor
Gunboats of Coastal Forces.
Post war records show that this type of minelaying was the most
effective of these categories.. Coastal Forces craft
minelaying was responsible for 53% of the total enemy casualties due to naval
minelaying for only 30% of the total number of mines laid offensively by all
surface minelaying. Aircraft carried out 72% of this type of operation and
caused 87% of the total casualties, a ratio
of 'casualties to mines laid', compared with for Coastal Forces. The ratio for large surface minelayers was
The following Table shows the results of Coastal Forces mining
Type of Craft
No. of Operations
No of Mines Laid
73 ships of 36,585 GRT Sunk including 38 warships, mainly escorts and
61 ships of 47,306 GRT Damaged.
Requirements for Minelaying Operations.
As a result of experience gained during Coastal Forces
minelaying in 1941 guidelines for future operations included:
To be carried out during
nights with no moon or minimal moonlight during the lay period.
state to be Slight or less.
Wind to be 'off-shore' to
reduce chance of engine noise being heard ashore.
to be neither extreme nor less than two miles.
attention to be paid to the availability of echo-sounding and Taut Wire
additional officer always to be carried to deal with navigational matters.
Coastal Forces craft were deployed for minelaying duty as
required by any requirement not necessarily included in the current programme
of patrol or planned action against enemy shipping or minesweepers. Craft were
not always deployed with their own Flotilla and could be operated independently
or with other Coastal Forces units. The easy conversion of this type of warship
allowed great flexibility in their use to meet urgent requirements and to
substitute at short notice as a replacement for another under repair.
Offensive Mining in Home Waters
It should be noted that Coastal Forces Flotillas are identified
in this text with a numerical prefix to the allocated Flotilla Number (e.g.,
4th MTB Flotilla - 4MTB).
Coastal Forces minelaying began on 7 January 1941 when 2 MTB's
from 4MTB at Felixstowe laid eight ground mines off the Dutch coast in ZuydcotePass. This
was the first of a series of minelaying operations ("PW") in
Nore Command which were replaced in September by two new
identities (QK and QL). Motor Launches (ML's) were first employed during June
1941 in Dover Command when 50ML began the "NL" Series off the FrenchCoast.
For the next year minelaying in both of these areas was
undertaken by ML's of the 50ML based at Dover and
51ML at Felixstowe which began operations in September 1941. These were all
intended to disrupt movement of enemy shipping along the coastline of the
A new series off operations ("KB") aimed at coastal
traffic off the Cherbourg Peninsular was started in June 1942 at Portsmouth by
the 52nd ML Flotilla, manned by the Royal Norwegian Navy. Only one was
completed as this Flotilla was transferred to Dover to
increase the minelaying resources needed in Dover Comnand.
Adjustments to the areas selected for mining in
Nore and Dover Commands were made during 1942 with the introduction
of new identities for minelaying operations - "NU" in
Nore with "NP" and "NQ" used in Dover
Command. Minesweeping Obstructors were laid for the
first time off the Dutch coast in April 1942 as were Sterilisers to terminate
the active life of ground mines after a predetermined interval. An acoustic
variant of the Mk XVI moored mine was initially laid on 3 October 1942 off
Gravelines by 50ML from Dover
("NP51"). Moored Magnetic Mines and a new design of moored mine
incorporating a snag line were also introduced in the
latter months of 1942.
Minelaying operations against coastal traffic and enemy
minesweeping operations was continued in
Nore and Dover Commands using only ML Flotillas until
February 1943. Motor Torpedo Boats of 6MTB based at Dover were
then deployed for the first time off Etaples for
"NL77", followed in May by a lay off Ymuiden
by 21MIB based at Lowestoft,
"QU11". Motor Gunboats were first used in the same month near Hook
of Holland for Operation "QL5A".
MIB's were increasing deployed came during 1943 and 1944
but never to the same extent as ML's.
Minelaying off the Cherbourg Peninsular and Brittany began in
Plymouth Ccmnand in April 1943 with a new series of
operations ("HOSTILE") against coastal shipping by the 10th Motor
Launch Flotilla recently converted for minelaying operations. This Flotilla was
frequently deployed for defensive patrols against E-Boat incursions in Plymouth
Command which reduced their minelaying availability. The navigational aid
"QH" was used by craft in Plymouth Command mining areas from April
1944 and later fitted to minelayers in the other Commands.
Before the Normandy
(Operation NEPTUNE) changes were made to extend the Dover Command
limits. The minelaying plan for NEPTUNE was
identified as Operation MAPLE and required minefields in Portsmouth Command to
protect naval forces during the assault on the French coast. Mines were to be
laid by aircraft and ships with a significant contribution from Coastal Forces.
The 14th MTB Flotilla based at Portsmouth began
a new series of minelaying operations ("KN") in the Cherbourg and Le
Havre approaches (SCALLOPS and GREENGAGE areas),
to supplement those by aircraft. At the same time minelaying in Plymouth, Dover and
Nore Commands by coastal craft against enemy coastal
traffic was intensified.
Motor Torpedo Boat No.234, Vosper-type
Improved Design of Mines
Specially prepared Moored and Ground mines incorporating the
latest techniques were used progressively for the Coastal Forces operations.
New types of specially prepared assembly allowing mixtures of different types
of detonating circuit, including some designed to attack specific types of
craft, were brought into use for minelaying operations in 1944. Details of the
various types of mine laid and the stowage capacity of each
type of Coastal Forces craft are provided below.
Minelaying Support for NEPTUNE
In order to increase the minelaying resources available to meet
the MAPLE requirement MTBs of the 14th and 64th
Flotillas were transferred to Portsmouth in
May 1944. A special diversion operation, including a minelay
by these MTB's (Operation MONASTIC) was carried out
on "D - 1" and some "KN" Series minelays
in the beach head area were carried out under the direction of the Naval
Commander Eastern Task Force during the early stages of the assault.
After an increase in enemy activity by light surface forces
during mid July 64MTB were detached to operate from Plymouth for
two minelays in the approaches to Brest.
Towards the end of 1944 increased U-Boat activity in Portsmouth Command made
necessary the provision of deep minefields at focal points on supply routes to
French ports (Operation BRAZIER). The 64th MTB Flotilla returned to Portsmouth in
January 1945 and carried out 13 minelays in the
BRAZIER series and on completion joined Nore Command
for normal Flotilla duties. The extension of these new minefields in the
Channel (Operation BUTTERMILK) was assisted by the transfer of the 10th, 50th
and 51st Flotillas to Portsmouth from Plymouth, Dover and
Nore Commands in March 1945. After eight minelaying operations
they returned to their previous Command areas.
Operations in Mediterranean Area
Only three minelaying operations were carried out. The first was
undertaken by the 10th MTB Flotilla which based at MersaMatruh. Two boats (MTB 68 and MTB215) were fitted for
minelaying in October 1941 for an operation in Bardia
harbour. Two ground mines and two floating ("R") mines were laid by
each craft with little interference. This was the only minelay
by Coastal Forces in the Eastern Mediterranean.
During 1943 after a stock of US Mk 6 moored contact mines became
available, three boats of the 10the MTB Flotilla (MTB 265, 266 and 316), then
transferred to the western Mediterranean, were
converted for minelayig off the Tunisian coast. Eight
fields made up of 118 mines were laid off PlaneIsland and
Bizerta. In one operation on 12 March 1943 MTB 316 and MTB
265 engaged four German 'R-Boats', one of which is known to have been damaged.
Coastal shipping from Leghorn was
selected for attention in March 1944 and the 8th Motor Launch Flotilla based at
Algierswere prepared for minelaying duties. On completion of
conversion the Flotilla transferred to Malta for
Operation NITWIT. Six MLs made up the minelaying
force which completed a lay of 36 Moored Mk XVU mines south of
Vadda Rocks near Leghorn on 16 May 1945-
Details of operations in Home Waters and the Mediterranean are
Coastal Forces mining operations were responsible for
significant losses and extensive damage to enemy coastal shipping. Traffic in
the English Channel was severely disrupted
and the load on his minesweeping resources stretched to capacity. They also
caused many delays due to losses and damage to minesweepers and escorts.
Movement of enemy shipping through the English
Channel and in the Bay of Biscay
Channel became dependant upon major routine
minesweeping with a constant high risk of casualties. Operations by Coastal
Forces craft were usually undetected and mines were laid with great accuracy,
especially after the radio navigational aid ("QH") became available
The effective deployment of Coastal Forces was attained at low
cost in ships, personnel and supporting facilities. 12 personnel were killed or
missing and 15 were wounded during minelaying operations. Ship losses were Two
ML's and one MTB with ten craft damaged.
The easy conversion for minelaying allowed speedy deployment to
satisfy special un programmed requirements or to increase the minelaying
capacity required for particular operations such as NEPTUNE support (MAPLE),
and additional deep fields (BRAZIER and BUTTERMILK).
Details of the various types of mine used is provided on Page 4.
Many sophisticated variants of both contact and ground mines were progressively
developed due to improvements in technology after 1939. Modifications and
design changes incorporated devices to make any enemy mine countermeasures as
difficult as possible, and to make direct attacks on minesweepers and mine
destructor vessels (Sperrbrechers).
Due recognition must be given to the support facilities and
skills available throughout the conflict at all operational bases. Without
these the high availability of craft and personnel would not have been
It was however the competence and bravery of those who manned
these craft to whom greatest credit must be given for the undoubted success of
Coastal Forces minelaying. They faced many dangers other than the ever present
hazards of the sea and weather. Operations in coastal waters introduced
significant problems due to shifting sands and difficult tidal conditions. In
addition they faced instant death due to both enemy and British mines already
extensively laid in the transit areas to selected minelaying positions. Any
explosion affecting a small petrol driven craft would
allow little opportunity for fire-fighting as in a large warship. Minelayers
deployed in enemy coastal waters were also continually vulnerable to attack by
enemy surface forces and aircraft. Duty in Coastal Forces and especially whilst
engaged in minelaying operations was an unenviable task.
British Mining Operations 1939 - 1945 (BR
WAR AT SEA by W. S. Roskill.
THE BATTLE OF
THE NARROWSEAS by Peter Scott.
Locations of Minelaying Operations in Home
Waters and Flotillas used
Identity of Operation
Geographic area of Minelay
Schedlt Estuary, Breedt Banks,
Last Operation PW23 (19/ 1/42
51ML and MGB
Replaced PW. First Lay QK7 (6/9/41).
Bankenberg, East Scheldt.
Last Operation QK4D (9/6/43).
51ML, 21MIB and MGB
First Lay QL1 (1/9/41).
Hook of Holland, East
Extension of Command area to Texel (11/42)
First Lay QU1 (5/11/42)
of Holland, Scheldt.
Last lay QU36 - Maple Phase m (29/5/44).
Command - French and BelgianCoasts
Extended to Le
First Lay NL1 (7/6/41)
9MIB, 22MTB, 13MTB
Staples and Sandgatte, West Hinder,
Part of MAPLE Phases II & III
Last lay NL136 after 18/7/44.
First Lay NP7 (14.11.41)
Last Lay NP51A (2/10/42)
Not continued - Mined area ?
Command - FrenchCoast.
NEPTUNE Assault area from 4/44
MAPLE Phases I, II and IV.
51ML 13MTB 14MTB
Havre (SCALLOPS PLUS),
21MTB, 22MTB, 64MTB
Last lay KN25 - Cherbourg (3/6/44)
Diversion and Minelay (5/6/44).
Cap d'Antifer (Operation TAXABLE) (5/6/44).
Deep A/S Fields in Channel
(See Text) (5/1/45 to 3/2/45)
10ML, 50ML. 52ML
Deep A/S Fields in Channel
(See Text) (20/3/45 -
Command - FrenchCoast between
MAPLE Phases II and III.
First Lay HOSTILE 3 (4/4/43).
Last lays HOSTILE 41 (25/7/45)
Types of Mine laid by Coastal Forces Craft
Moored Contact Mines
For Anti-submarine Fields in Channel. Switched Horn Type.
Mk XVII (Assembly 6)
Acoustic Influence Type
Mk XVII (49/50)
Two speed acoustic assembly with delayed release sinker
Small anti-submarine mine used in coastal waters from
Modified Mk XXVII
Switched Horn and Snag Line for coastal waters
US Mk 6
Used in 1943 by 10MTB off Tunisia
First used in NL21A on 6/5/42
magnetic mine for use in coastal craft
AMk I – IV
Introduced in Sept to
replace aircraft type. Available as combined acoustic and magnetic mine in
1943. Other changes incorporated to defeat sweeping methods. Special
Assemblies B231, B233, D413 D4l5 and D407. MXC 15 Assemblies used after 10 May 1944
during MAPLE Phase III to attack E-Boats.
Heavy Ground Mine first laid in 1942. Explosive Charge 1,750lb
Minol. Used in depths of 6 to fathoms. Fitted with
arming clock and steriliser. Unsatisfactory in service in 1942.
Introduced in 1944 for MAPLE. Improved Acoustic/Magnetic type.
Special Assemblies D411 and K1011 Unit added in 1944 to attack small fast
Laid to destroy mine
Replacement from 6/42
Used infrequently off Norway and
Coastal Forces Craft Details and designed Mine Stowage Capacity
Motor Launch No.187, Fairmile B-type
ML - Fairmile A
8 Ground *
ML - Fairmile B
MTB - Fairmile B
MTB - BPB and Vosper
MGB – BPB
Note * or combinations of both types.
6. TYPES OF BRITISH MINES USED BETWEEN 1939 AND 1945 BY SURFACE
Explosive Content (lbs)
and Mk XII
WW1 Mine Existing Stock used in Dover Barrage and East Coast
Modified H2 (1926). Used in Barriers until 1940
General Purpose mine used in WW2 and modified for us as
Acoustic Mine if required
Coastal Forces craft only
Anti-submarine mine using XVII Case. Unsatisfactory in
service. Replaced by Mk XXII
Modified Mk XX used in Northern Barrage from 1942
Switch Horn with
Snag Line attached
Modified Mk XXII used by Coastal Forces craft.
Switch Horn with
Snag Line attached
Modified Mk XXII used by Coastal Forces craft.
Moored Magnetic Mine in General Use after 1940. Pre-Production
stock used in late 1940
A Mk 1 to IV
Initially Magnetic. Later incorporated Acoustic and combined