Contents continued from Part 1 5. Minelaying by Light Coastal Forces  in Home Waters And Mediterranean, 1940 to 1945   6. Types of British Mines Used between 1939 and 1945 by Surface Minelayers

 

 

 

5. MINELAYING BY LIGHT COASTAL FORCES IN HOME WATERS AND MEDITERRANEAN, 1940 TO 1945

 

(for more ship information, go to Naval History Homepage and type name in Site Search)

 

 

Introduction

 

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 Forces.

 

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 1: 30 ratio of 'casualties to mines laid', compared with 1: 48 for Coastal Forces. The ratio for large surface minelayers was 1: 250.

 

The following Table shows the results of Coastal Forces mining operations:

 

Type of Craft	No. of Operations	No of Mines Laid
ML	820	4,718
MTB	425	2,248
MGB	12	48
Totals	1,257	7,014

 

 Sinkings: 73 ships of 36,585 GRT Sunk including 38 warships, mainly escorts and minesweepers).

 Damaged 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.

 

Sea state to be Slight or less.

 

Wind to be 'off-shore' to reduce chance of engine noise being heard ashore.

 

Visibility to be neither extreme nor less than two miles.

 

Particular attention to be paid to the availability of echo-sounding and Taut Wire measuring gear.

 

An 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 Zuydcote Pass. 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 French Coast.

 

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 occupied countries.

 

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 landings (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 Mersa Matruh. 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 Plane Island 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 Algiers were 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 given below.

 

Conclusions

 

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 in 1944.

 

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 possible.

 

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.

 

Sources:

 

British Mining Operations 1939 - 1945 (BR 1736(46).

WAR AT SEA by W. S. Roskill.

THE BATTLE OF THE NARROW SEAS by Peter Scott.

 

 

 

Locations of Minelaying Operations in Home Waters and Flotillas used

 

Flotillas Involved	Identity of Operation	Geographic area of Minelay
NORE COMMAND
4MTB	PW	Netherlands Coast.
		Zuydote Pass, Schedlt Estuary, Breedt Banks,
		Gravelines and West Deep.
		Last Operation PW23 (19/ 1/42)
51ML and MGB	QK	Replaced PW. First Lay QK7 (6/9/41).
		Schoonveldt, Ostend, Bankenberg, East Scheldt.
		Last Operation QK4D (9/6/43).
51ML, 21MIB and MGB	QL	Replaced PW.
		First Lay QL1 (1/9/41).
		Hook of Holland, East Scheldt, Scheveningen.
51ML, 22MTB	QU	Extension of Command area to Texel (11/42)
21MTB, MGB		First Lay QU1 (5/11/42)
		Ymuiden, Texel, Scheveningen
		Egmond, Hook of Holland, Scheldt.
		Last lay QU36 - Maple Phase m (29/5/44).
DOVER COMMAND French and Belgian Coasts Extended to Le Havre (28/5/44)
50ML, 52ML.	NL	First Lay NL1 (7/6/41)
		Boulogne, Calais, Gravelines,
9MIB, 22MTB, 13MTB		Dunkirk, Staples and Sandgatte, West Hinder,
		Ostend, Blankenberg Nieuport, Zebrugge
		Part of MAPLE Phases II & III
.		Last lay NL136 after 18/7/44.
	NP	First Lay NP7 (14.11.41)
		Ruytingen, Calais,
		Last Lay NP51A (2/10/42)
		Not continued - Mined area ?
PORTSMOUTH COMMAND French Coast. NEPTUNE Assault area from 4/44 MAPLE Phases I, II and IV.
51ML 13MTB 14MTB	KN	Fecamp, Le Havre (SCALLOPS PLUS),
21MTB, 22MTB, 64MTB		Barfleur, Cherbourg (GREENGAGE PLUS)
		Last lay KN25 - Cherbourg (3/6/44)
.	MONASTIC	NEPTUNE Diversion and Minelay (5/6/44).
14MTB, 64MTB	BRAZIER	Cap d'Antifer (Operation TAXABLE) (5/6/44).
64MTB	-	Deep A/S Fields in Channel
		(See Text) (5/1/45 to 3/2/45)
10ML, 50ML. 52ML	BUTTERMILK	Deep A/S Fields in Channel
		(See Text) (20/3/45 - 6/4/45)
PLYMOUTH COMMAND French Coast between Cherbourg and Brest
10ML, 64MTB	HOSTILE	MAPLE Phases II and III.
		First Lay HOSTILE 3 (4/4/43).
		Lannion, Channel Islands, Brittany Coast
		Last lays HOSTILE 41 (25/7/45)

 

 

 

Types of Mine laid by Coastal Forces Craft

 

Mine	Type	Remarks
Moored Contact Mines	Mk XVII	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
	Mk XIX	Small anti-submarine mine used in coastal waters from September 1941
	Mk XXV	Modified Mk XXVII
	Mk XXVII	Switched Horn and Snag Line for coastal waters
	US Mk 6	Used in 1943 by 10MTB off Tunisia
Moored Magnetic	M Mk1	First used in NL21A on 6/5/42
Ground Mines	AMk	Modified aircraft 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.
	AMk III	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.
	AMk VI	Introduced in 1944 for MAPLE. Improved Acoustic/Magnetic type. Special Assemblies D411 and K1011 Unit added in 1944 to attack small fast targets.
Obstructors		Laid to destroy mine sweeps
	Mk1	Replacement from 6/42
Floating Mine	R Type	Used infrequently off Norway and in Mediterranean

 

 

 

Coastal Forces Craft Details and designed Mine Stowage Capacity

 

Motor Launch No.187, Fairmile B-type

 

Type	Displacement (Tons)	Speed (Knots)	Mine stowage
ML - Fairmile A	57	25	9 Moored*
			8 Ground *
ML - Fairmile B	73	17	9 Moored*
			8 Ground*
MTB - Fairmile B	102	29	10 Moored
MTB - BPB and Vosper	37	39	4 Ground
MGB – BPB	28	39-42	4 Ground

 

Note * or combinations of both types.

 

 

 

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6. TYPES OF BRITISH MINES USED BETWEEN 1939 AND 1945 BY SURFACE MINELAYERS

 

 

 

Type	Explosive Content (lbs)	Detonation Method	Sinker Type	Remarks
H2	320	Hertz Horn	Mk VIII and Mk XII	WW1 Mine Existing Stock used in Dover Barrage and East Coast Barrier.
Mk XIV	320 or 500	Hertz Horn	Mk XV	Modified H2 (1926). Used in Barriers until 1940
Mk XVII	320 or 500	Switch Horn or Acoustic Influence	Mk XV Mk XVII Mk XVIII	General Purpose mine used in WW2 and modified for us as Acoustic Mine if required
Mk XIX	100	Switch Horn	Mk XIX	Coastal Forces craft only
Mk XX	320 or 500	Antenna	Mk XVII	Anti-submarine mine using XVII Case. Unsatisfactory in service. Replaced by Mk XXII
Mk XXII	320 or 500	Switch Horn	Mk XVII	Modified Mk XX used in Northern Barrage from 1942
Mk XIV	500	Switch Horn with Snag Line attached	Mk XVII	Modified Mk XXII used by Coastal Forces craft.
Mk XXVII	100	Switch Horn with Snag Line attached	Mk XIX	Modified Mk XXII used by Coastal Forces craft.
M Mk1	320 or 500	Magnetic influence	Mk XV Mk XVII	Moored Magnetic Mine in General Use after 1940. Pre-Production stock used in late 1940
A Mk 1 to IV	750	Influenced Ground	None	Initially Magnetic. Later incorporated Acoustic and combined Magnetic/Acoustic circuits