Mine Laying Operations 103 Squadron and 576 Squadron
Nice artwork of a Wellington mining at low level
The RAF sea mining campaign during WW2 was extremely successful and cost effective disrupting German naval and merchant movements along the coast of occupied Europe. It was arguably a far more productive use of resources than the continual area bombing attacks throughout the war and would have justified more commitment.
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Two sea mines on bomb trolleys awaiting loading onto nearby Handley Page Hampdens early in war the foreground
Gardening or vegetable planting were the code names for airborne sea mining operations. These were carried out at the request of the Admiralty to disrupt German sea traffic around the European coast in respect of both warships and merchant ships.
Bomber Command were given the responsibility for the airborne operations with Royal Navy Officers attached to all Bomber Group HQs to co-ordinate these operations designating where and when and with what type of mines these were to be carried out. The naval officers had no responsibility for the routing of these operations or the operational tactics.
The purpose of the mining campaign was :-
1 To dislocate enemy seaborne traffic around the coasts of Europe,
2/ To assist in the Battle of the Atlantic by harassing the passage of U Boats leaving and entering the French west coast bases. Also U Boat training in the Baltic
3/ To harass blockade runners arrival and departure using the Gironde River, Bayonne and St Jean de Luz.
4/ To hinder passage of enemy naval surface units.
5/ To force the enemy to maintain large numbers of experienced personnel and valuable material for the clearance and regular sweeping harbours and channels.
The seaborne traffic mainly consisted of raw materials desperately required by the German industries – iron ore for Norway, Sweden, Spain and the west coast French ports. Also ball bearings and wood from Sweden
The shortage of large German freighters forced the use of small coastal vessels and a large proportion of German manufactured goods and raw materials was carried by inland waterways which reached the coast and became targets for mining operations.
The U Boat bases at Brest Lorient St Nazaire la Rochelle and Bordeaux were regularly mined. German units along the Norwegian coast were continually harassed by mining and through into the Baltic.
The German mine sweeping force consisted of hundreds of vessels and ten of thousands of highly trained personnel. About 50 large merchant vessels were converted to flak ships and magnetic acoustic mine sweepers with reinforced hulls referred to as Sperrbrecher ( pathfinder or mine barrage breaker ). These had displacements of around 10000 tons and most convoys were proceeded by at least one of these vessels.
Air sea mine laying was pioneered by the Germans from the start of the war. The RAF commenced their mine laying campaign in 1940. The AOC 5 Group Sir Arthur Harris was prominent in this and the first sea mines were laid by Hampden aircraft. On 13 April 1940, days after Germany's invasion of Norway, a large number of Hampdens were dispatched on night-time mine laying flights in North Sea in areas unapproachable by British naval units. These sorties proved highly effective in disrupting German naval movements with a casualty rate of less than 1.9 aircraft per mission.
Between April 1940 and April 1943 aircraft laid approx 20000 mines. The mining areas were referred to as gardens and each given the name of a flower or vegetable or in a few cases fruit shellfish or fish.
During this period 500 enemy ships were sunk or damaged which was a considerable contribution to the UK war effort.
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The mines were laid on a timed run visual pin point of the enemy coast at a height of 1000 ft to 1500 ft. When Lancasters were used and H2S ground mapping radar became available the dropping altitude was increased to around 5000 ft to 6000 ft. Each Wellington carried 2 x 1500 lb mines whilst the Lancasters could carry up to 6.
The primary objective was to lay the mines in the enemy's swept channels or waterways which were very narrow and seldom more than a mile wide. These channels were always well known through careful intelligence work and plotting and the information was regularly updated.
From a naval point of view it was desirable to drop the mines from as low as possible and not from above 1500 ft for technical reasons due to the fusing. Dropping at these altitudes made the aircraft very vulnerable to light and medium flak.
Gee was a useful aid to navigate to a visual pin point but dropping on Gee was forbidden due to inherent errors in the system.
From the visual pin point the mine laying aircraft had to make a timed run on a steady course and speed with a ground speed of 180 mph recommended and certainly not more that 200 mph otherwise the parachute could be pulled from its load. Crews were briefed not to exceed a run of 12 miles if at all possible although the Navy were never really happy about this and certainly never in excess of 30 miles from the last Gee fix.
Usually the mines were dropped at three second intervals in case of the Lancasters and 5 seconds for the Wellingtons. Crews were instructed to maintain the same steady course for two or three minutes after release if possible in order to deceive the enemy regarding the exact position the mines were dropped.
In the event of any uncertainty in the exact dropping location the pilots were instructed to return to base with their mines. The reason being that these mines were in short supply and could be used again if brought back. Because of the method of arming the mines aircraft could land quite safely with them still on board and in the event of a crash or crash landing there was little chance of an explosion which was the case with a normal bomb load.
In the event of mines having to be jettisoned then it was stipulated that this had to be in safe mode and in deep water to avoid them falling into the hands of the Germans. The position had to be noted.
It was prohibited for mines to be jettison within 60 miles of the UK east coast and within 30 miles of the south coast even in a safe condition.
Every station held a complete set of Admiralty charts and datum positions were drawn over the relevant gardens. Targetting information was passed to each station by Group with times of high tide and low water which could effect the appearance of the coastline pin point. This data was copied out by the Station Intelligence Officer or a delegated subordinate and passed to the navigators concerned.
On completion of the operation details of the positions of every mine dropped, the aircraft headings and lats and longs were sent to Group HQ.
The mines used for these operations were cylindrical in shape with a wooden fairing at one end to facilitate entry into the water. There was a small parachute attached to the rear of the weapon. The type of mine was either magnetic or acoustic or both. It laid on the sea bed and therefore had to be in fairly shallow water so the explosion would have maximum effect. The weight of a standard mine was 1500 lbs including about half a ton of explosives.
The firing mechanism of the mine was contained in a water tight compartment and quite delicate. Mines were designed for specific and general purposes for example the F616 series anti submarine mines the B200 magnetic general purpose mine, the A108 anti Speerbrecher mine and the G700 acoustic/magnetic mine.
The general aim was a mine with some form of delay mechanism so that it was activated by the preceding minesweeper but did not detonate the mine till the next ship passed over it. Some mines were activated in this way but the delay could be hours or even a day or more than that. Some mines were armed magnetically and fired acoustically or visa versa.
The magnetic mines were actuated by magnetic field disturbance created by a ship passing through the water. It was very sensitive and once activated detonated very easily. The acoustic mine incorporated a vibration detector which reacted to noise such as ship's engines and auxiliary machinery which can be heard below water for considerable distances. In order to prevent the mine from detonating from noise some distance away the mechanism was set so that the mine detonated when the vessel passed directly overhead.
Both acoustic and magnetic mines were fitted with anti detonation devices so that detonation of other mines in the vicinity would not result in the detonation of nearby mines.
Methods of sweeping magnetic and acoustic mines were simple in principle but required special equipment. The aim was to detonate the mine at least 500 yards ahead in the case of the magnetic mine by transmitting a powerful magnetic pulse into the water. In the case of the acoustic mine by producing sound waves by some sort of electronic hammer or a acoustic fork.
All mines incorporated three safety devices.
1/ An ordinary safety fork similar to those fitted to aircraft bomb.
2/ A soluble plug or washer which took 40 mins to dissolve in sea water and which static switch operated the arming mechanism
3/ A hydrostatic switch which operated the arming mechanism when the water pressure was sufficiently high – around 5 fathoms or 30 feet.
It was therefore impossible for the mine to detonate even in the event of a forced landing or crash.
The results of mining operations were rarely known within a short time but from every point of view were considered to be a highly successful and cost effective operation against the enemy.
Aircraft losses on average were approx 2%.
The 20000 mines laid by Bomber Command between April 1940 and April 1943 are known to have cost the Germans 500 ships totalling 400000 tons at the cost of 300 aircraft.
This worked out at one ship per 40 mines. In the Baltic this increased to one ship per 12 mines.
The size of a vessel sunk or damaged was not necessarily a measure of its importance. As an example one small vessel that was sunk by mines was carrying a group of important German scientists who specialised in mine counter measures.
Coastal Command were also active in the sea mine laying campaign but the bulk of the work was done by Bomber Command.
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Post war it was confirmed by research that the results of the RAF WW2 sea mine laying campaign far exceeded the expectations at the time and were a vital contribution to the war effort.
Of interest is the mining of the Kiel Canal by Mosquitos of 8 PFF Group and in April 1944 was very effective and a month later Lancasters of 5 Group carried out the brilliant feat of mining the passage connecting Konigsberg and Pillau closing both ports for 13 days and Danzig for 15 days.
The mining of the Kiel Canal cost Germany an estimated 3000000 tons of cargo carrying capacity and 1400000 tons of imports none of which could be regained.
The aircraft of 1 Group were involve in laying in excess of 7000 mines between 1st April 1944 to the 30th June 1944. from the Biscay Franco Spanish frontier to the Gulf of Danzig including all the Atlantic ports. On one night Lancasters of 1 Group and 5 Group laid 450 mines in the Gulf of Danzig.
On the night of the 5/6 October 1944 9 Mosquitos laid mines in the Kiel Canal and this operation was rewarded immediately by the sinking of a 200 ton vessel which blocked the canal at Brunsbuttel.
U boats in particular were badly effected by the mining returning to their bases on the French west coast at Lorient and St Nazaire. It is said, although at the time of writing I have not been able to confirm this, that one U Boat actually detonated a mine whilst docking at St Nazaire and sank with all hands in front of a large group of senior German naval officers who were gathered along the dockside to welcome the returning crew.
These mine laying operations were not popular with the Bomber Command crews mainly because of the low dropping altitude which made the aircraft very vulnerable to the excellent German medium and light flak. However the whole effort was an mining effort was an excellent and cost effective campaign with losses on these mining operations about 2% which was significantly less than Bomber Command as a whole
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A 300 Polish Squadron Wellington at Hemswell awaiting its load of 2 sea mines on trailers in the foreground
A nice pic of 3 Hampdens with sea mines in foreground
Avro Lancaster being loaded with mines November 1943
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103 Squadron
Mine laying sorties 198 - Failed to Return 10 – Did not take off 4 – Early returns 6.
Crews missing – Those of Vickery, Emmott, Smith H B, Nicholson, Barr, Nimmo, Mitchell K R, Pearton, Slater, Hole
Items on the website of interest connected with this subject are :-
Sid Burton and crew
Nicholson and crew
Mine laying ops April 43.
576 Squadron
Mine laying sorties – 29 – Failed to return 2
Crews Missing – Those of Presland and Murray
Mine laying Operational Area Code Names
Item compiled by David Fell with photos from my archive
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