Gardenining - Aerial dropped sea mines 1940-2

   In April 1940 Bomber command were asked to commence laying magnetic mines in the North Sea and was the fruition of a project that the Admiralty had been developing since 1936. By June 1939 the first orders were arriving at the Admiralty and the Air staff requested thirty units to be placed at their disposal to be test dropped by torpedo bombers and a conference proposed to discuss the application and effect of the mine on warfare. The outbreak of the war delayed any response from the Admiralty but when they did finally contact the air ministry they were very optimistic about the deployment and potential informing them that 170 units would be available for the Fleet Air Arm and Bomber command to drop by the summer of 1940.

   Ever concerned by neutral opinion it was deemed necessary that they would alert the Germans and other nations of the vague area of the mine field so as to tie in with The Hague convention which was clear that all naval mines had to remain attached to their moorings in charted fields but as magnetic mines didn’t have moorings they were not specifically covered. The Admiralty liased closely with the Foreign office on how to proceed and were advised to avoid all neutral countries’ territorial waters even if unrecognised or disputed and to give four days’ notice so that they could with all of their embassies in the target area with enough time to give forty-eight hours’ notice. Similarly, the Admiralty would alert the BBC who would put out a notice at the same time as the Foreign office. All of this required the Air Ministry to give the Admiralty a week’s notice of the planned operation.

   Projections were made stating that the British would need to lay some 4636 mines using a total of eight squadrons laying some 460 per month in home waters, the Middle and Far East theatres if Italy and Japan were to join Germany. There was however a major problem with the mine’s deployment with the Air Staff revealing to the Naval staff on 19 September that Coastal command’s bombers, the Bristol Beaufort (the Blenheim’s stable mate) and Blackburn Botha were not entirely up to the task with the Botha’s range not extending past the Kiel canal and no other aircraft really suited to deploy it although tests on the upcoming Stirling and Halifax were being carried out. Another problem was that the mine’s mechanism was not really designed to withstand the impact on the water following an air drop and tests were undertaken with only a fuzing attachment to the torpedo dropping mechanism was added to both aircraft to rectify things. As an interim measure Coastal command did some tests using the obsolete Vickers Wellesley and found that they could drop the mines at 200 feet at a speed of 167 mph and that it had the range to be effective but in the same conversation they also stated there were no Wellesley squadrons in Britain and that the ministry had already decided the mines had to be dropped from no less than 500 feet and that they would continue to search for an adequate aircraft.

   By 1 December the Admiralty had perfected their trials and had set about having the outer casing of the mine strengthened to withstand the drop but they were optimistic that drops could now be achieved with production set at 80 in February, 180 in March and then 100 per month until the bulk order of some 980 were ready in November with this figures unalterable.

   The RAF had also developed a variant of the mine which, although not as effective as the original it could be dropped by Bomber Command aircraft without much modification. The Air ministry also advised that the best conditions for delivery of these bombs would be on moonlit nights with longer nights in the winter. A compromise was reached with the decision to have a massive concerted effort on the seven nights in April with the hoped result of total disruption of German shipping with the primary target being the Kiel fjord and the Elbe estuary with secondary targets at the Jade and Ems estuaries.

   Yet another problem was to rock the project as the number of Beauforts, only fourteen aircraft in

Coastal Command's Bristol Beaufort

March, meant that the operation had to be pushed back until June when forty would be available or convert the project to Hampdens of which seventy-two were available in February and projections of up to one hundred and fifty by June. The mines had to have their tail pieces refitted with drogues to allow them to be dropped from 500 feet at a Hampden’s cruising speed.

   Maurice Strefton of 49 Squadron described the approach:
one had to come down to three hundred feet to put the mine down. Not only for accuracy but you had to come down to the level because if it was dropped too high the mine would disintergrate but at three hundred feet it would hit the water and settle softly to the bottom of the canal or sea. (1)

   On the 3 February the Air Ministry wrote to the Admiralty to inform them that the Beauforts range of 350 miles when loaded may not be adequate to reach the target areas some 410 miles away but that the Hampden could, thought it could not go beyond Swinemunde scuppering the Admiralty’s hope of mining as far afield as Danzig!

   Careful planning and coordination between Coastal Command and the Ministry outlined target areas, landmarks and possible enemy opposition in W.A.15 which was originally issued to Coastal Command on 19 February. The prime targets areas were set with practicable locations being the Scheleswig coast to the Fehmarn Belt and from the Cadet Channel to Cap Arkona, with another off Peerd point, Ragen Island to the German coast no further than the 16˚ Meridian. The crews were briefed to drop their mines away off the coasts and out of sight of lighthouses, flak ships and any other landmarks so that the white impact splashes would not be observed by the light of the moon however the bombers should avoid coming between the moon and the shore so to avoid being silhouetted and observed. Operations should only be carried out by moonlight except in cases where features and landmarks were easy to locate in the dark.

   The predictions for loss were considered to be manageable with only those aircraft that were operating close to shorelines and harbours that might be detected and intercepted. The line of attack should be carried out at low level to avoid RDF detection and the idea of diversionary attacks were also suggested but these would need to be coordinated carefully.

   The implementation date was pushed to April as the two Coastal Command squadrons were being converted to Beauforts and the Hampden squadrons on loan would require intensive training in navigation and pinpoint accuracy drops at low level with the seven-day moon period in March was considered to be ideal. The operation or “Gardening” missions were to put the maximum amount of aircraft and mines out on the first night and as many available on the following nights with the aim of planting a patch thoroughly within a week.

   As late as the 11 March Coastal Command were still unhappy about the target areas suggested by the ministry warning that some were deeper than the five fathoms prerequisite and they also appraised that it would be better if a small force of highly trained pilots mined smaller areas accurately rather than an airfleet of semi trained crews attempting to mine a wider area poorly. The Air Ministry were anxious to get on with the mission and though it understood Coastal Command’s concerns they felt that even if inaccurate, a wider field would be more damaging to shipping and the mines wouldn’t be dropped in the shallows as they might be recovered by the Germans intact. A further set back to the use of Hampdens came on 8 March at a joint Navy and Airforce Technical branch meeting where it was revealed that the parachute fitted to the mine was not adequate to be dropped at the required 200 mph. Not wanting to go off “half cock” with the small amount of Beauforts available the Ministry and Admiralty decided to postpone until they had a suitable replacement. Luckily a chute under development at Woolwich for star shells was tested at Farnborough the following week to much success.

   With the parachutes now working, two squadrons, 49 and 83 were loaned to Coastal Command and training programme was instituted whilst tests were carried out at Pembroke docks to register splash visibility using oil drums full of sand. Further tests were carried out using a concrete dummy which weighed closer to the 1500 lb of the real mines. The major concern was that the white splash of the mine’s impact on the sea would be seen reflected in the moonlight.

   Mine production was still nowhere near adequate levels and a further 3000 units were ordered on top of the previous 980 as the proposed operations in Arpil would consist of one squadron of Beauforts and six squadrons of Hampdens! The Air Ministry allocated 200 mines with 155 going to the Hampden squadrons and the Admiralty providing personnel to advise mine handling at each airfield.

   With the final preparations completed the orders were sent out to the squadrons that Kiel, Elbe and Lubesck should be prioritised with thirty-eight mines each carried out by the Hampdens of Bomber Command.  The two Commands should coordinate on the best time to carry out the attack and not let the weather interfere too much. If the Baltic weather was unsuitable then the North Sea must be attempted and vice versa. The operation must go on. After exhaustive reconnaissance of the areas it was decided to drop mines on Schillig Roads and Kiel Fjord on clear moonless nights as well where possible.

   The signal to begin came through on 8 April with Coastal Command scheduled to begin on the 12/13 April at Schilling Roads and Elbe hoping to catch returning German warships who had been engaged in Norway but bad weather cancelled it. The Hampdens made their first raid the following night operating   from bases at Scampton, Hemswell and Waddington.

   Each area mined was given a letter with a corresponding vegetable such as Yams for the Jade estuary (Y) with mines being referred to as “vegetables” bit it wasn’t the only duty for the aircraft as on the 26 April it was requested that returning aircraft should machine gun the Luftwaffe’s seaplane bases around the Heligoland Bight to try and alleviate the pressure placed on British shipping in the Thames estuary from the German’s mining operations.

   The Admiralty’s Fleet Arm Swordfish of 815 squadron were also brought in to assist the proves of mining with their first Gardening operation in the Wester Ems on 27 April. The lion’s share of the planting was done by the Hampdens who dropped 109 in the Elbe, Kiel canal and other targets but fog had interfered and operations after the 25 April had to be cancelled.

   The Beauforts were temporarily withdrawn from Gardening for operations against Stavangar and against the German fleet or the liners SS Europa and SS Bremen which had been used to transfer Wehrmacht units to Norway. Four of the Beauforts were permanently detached for anti-shipping operations from 4 May with the rest of 22 Squadron returning to Gardening operations.

   May saw plans for the expansion of these missions with production of mines reaching four hundred per month with the parachute production expected to keep up and a greater expectation on the air crews being able to operate on clear starlight nights as well as the moon phase. So optimistic were the Admiralty that they wanted more aircraft to take part where they and excess stores of mines were available. Studies were made of German losses in the fields already “planted”, areas which had been swept by the Kriegsmarine’s units and new fields were looked at with reconnaissance reports scrutinised in depth as to their suitability. With German military policy being active in maritime operations with Wesserung and threatening the Low Countries the Admiralty, whose ships were held down with other duties believed that mining German waters was the best course of action to slow German movements. Through April eleven vessels had been sunk including eight German, one train ferry and two unknown vessels and a further five damaged. The RAF and Admiralty were reliant on foreign news agencies and sources but with the German invasion of Holland these sources quickly dried up leaving them almost blind as to what damage had been caused. There were no reports from the Jade and Wesser estuaries as the German press understandably kept news of any sinkings quite. By June reports came back that a total of fourteen German vessels (including two minesweepers) and ten neutral vessels had been successfully mined but there might have been more, whilst further news came in that Deflziji had to close and the Kriegsmarine ordered to sweep the area taking four days seriously disrupting traffic to the Ruhr and costing two vessels. The Kiel canal was also closed to neutral shipping with all marine lighting west of 12˚ 25 ‘E were switched off and Finnish shipping agents raising insurance by fifty percent for all ships going to Germany from the 23 April whilst one of their shipping lines suspending all routes to their ally because of the danger posed by the mines.

   Following the fall of France and the commencement of Operation Seelöwe the Gardening

Bomber Command's Hampdens

operations became even more important with the Admiralty even proposing mining British ports and estuaries to dry them to the German invaders. This would be solely a Coastal Command operation as the Hampdens would be ear marked with trying to intercept the invasion fleet in the channel or attack French ports. It was a situation that Coastal Command were unable to deal with as their Beauforts were undergoing engine replacements and they requested assistance from the Fleet Air Arm for any suitable aircraft should the situation arise.

   Until that time however operations were expanded to include Dunkirk and Boulogne as well as East Scheldt and Maas Delta all of which were planted on the 26 June and between 3 and 5 July respectively. Bomber Command requested that they be completely relieved from Gardening missions through August in favour of active bombing campaign against the multitude of German targets but this was overruled by the Admiralty and the Air Ministry with a limited operation of six aircraft being retained. The Admiralty believed that keeping up the pressure by the constant laying of mines would not give the Germans time to overhaul their minesweepers but a grateful Admiralty did send a telegram of thanks to the minelaying squadrons who by the end of August had laid 780 mines with almost two thirds of those carried out by the Hampden squadrons.

   All operations were suspended for tests to the mines in early September and again in the middle of the month as the Admiralty were concerned about the mines interfering with the fleet’s manoeuvres but Le Havre (the Anemones patch) was first mined by 812 squadron’s Swordfish because of the large concentration of invasion barges and small support craft that was building up in the port whist a detachment of 42 Squadron’s Blenheims mined the area off Lorient. In October the bombers only mined one new area in the east of Scheldt near Terneusen by the Swordfish of 812 who laid the throughout the month. The area, like Le Havre was a major artery for invasion barges and traffic which was coming through the Terneuzen - Ghent Canals. On 23 November though the Admiralty had requested that the RAF no longer concentrate on the lines of communication and distribution along the Dutch and Belgian coasts but to concentrate on the German base ports themselves with the top catogary of targets being Kiel and Baltic ports, Elbe, Jade and Ems Rivers, Brest, Lorient and Gironde river with the invasion ports and Seine estuary falling to the lowest catogary which were only to be mined if specifically ordered. The Admiralty believed that the more important the base the more resources would be expended to sweep and keep the sea lanes open. They also believed that one raid on each port laying twenty-four mines would be sufficient to cover all the targets with 336 for Class A, 156 for Class B and 48 for Class C with none for D unless specifically called to do so. This figure was currently well above the best of previous operations but the Admiralty, although accepting that there was a shortage of aircraft and crews with other duties often taking priority but they also appraised the crews as having become experts and more precise in their accuracy and with mine production at a steady 700 units per month there would still be a monthly surplus.

   The Air Ministry were sceptical about the ability of their squadrons to carry out the Admiralty’s projections and their own forecasts showed that five squadrons of sixteen aircraft would be needed to be able to meet the demand. With Coastal Command not having enough aircraft it meant that they would either have to call on Bomber command to assist regularly or to permanently allocate three bomber squadrons to Coastal Command so as to alleviate Bomber Command of massed Gardening operations but effectively cutting into their established numbers. The Deputy Chief of Air Staff believed that;
The effect of our mining has been an outstanding contribution to our war effort. Had we the means it might have already proved a decisive factor in the Sea War. It may still do so. 2

   He continued to opine that they needed to maintain their size of force and also suggested that the Expansion and re-equipment Policy Committee should allow the allocation of some of the newer Manchester and Stirling bombers which could range as far as the Baltic and would give these aircraft an easy test operation for range and acclimatisation of crews without coming across serious opposition.

   Although Bomber Command’s Hampdens were still doing the majority of the sorties through October and November they were going down in number (63 in October and 55 in November) which alarmed the Admiralty who were keen to up the pressure on Axis submarine ports at Lorient and Bordeux as well as the Kiel Canal which was used by U-boats and the Bismarck and the Tirpitz when they were commissioned. The Air Ministry responded on Boxing Day 1940 saying that they would make new aircraft and crews available to the mining operations where appropriate.

   Bomber Command were anxious to use their aircraft on an active campaign against German industry and Oil and were suffering losses in this campaign which meant less aircraft were available for Gardening. Adverse weather also made the operations through the winter of 1940 difficult and it was hoped that when the bigger, heavier four-engine bombers became available they would be able to carry three or five mines which would greatly assist in reaching the Admiralty’s quota. This was agreed by the Expansion and re-equipment Policy committee on 19 December with 7 Squadron’s Stirlings and 207 Squadron’s Manchesters which would release the Hampdens back to bombing operations. Bomber Command reported that a Stirling’s maximum payload was six mines but for optimum range they would carry three whilst the Manchester carried five which meant that Coastal Command could utilise one such squadron and meet the Admiralty’s quota with ease and plant a whole patch in a single sortie.

   On 19 December mining operations in the Channel recommenced with a new type of mine fitted with a steriliser which gave the mine an operational life of six weeks rather than a year which meant that the Admiralty could operate without worrying about sailing into their own minefields but still keep up pressure on the Germans who, it was hoped might believe the old patches were “safe” and start using them again. The old type mines were still “planted” in the Seine and introduced to Dieppe and St Malo where as the steriliser fitted mines were introduced to the Channel ports of Boulogne, Calais, Zeebrugge, Dunkirk, Le Havre and Flushing, however these new mines were not properly introduced until April 1941.

  In December Coastal Command’s seconded Swordfish of 812 squadron mined an area off Brest that the Hampdens had mined in August and October and in the Seine estuary on the 8 December. The patches were still ever changing with the Channel still closed and with German Flak batteries being deployed along estuaries and ports which had to be avoided. Following the October mining in the approaches to Brest the field flight path’s had to be changed to avoid the strengthened German flak defences but still being able to effectively mine the mouth of the harbour. The same was also true for Lorient harbour. This attention to detail gave the crews a sense of security and routine especially compared to missions over Germany and the well-defended Naval bases at Kiel and Wilhelmshaven and they probably shared Coastal Command’s evaluation:

Nowadays everyone treats Gardening in quite a nonchalant way, except that there are one or two gardens in rather sticky localities such as round the mouth of the Scheldt, and gardens off Brest. 3

   The missions also gave opportunity for the crews to fins other targets to strafe and bomb such as shipping or on rare occaisions attacking the Luftwaffe;

   As we crossed over Cherbourg on the way home an aircraft passed us going in the opposite direction with his navigation lights on. This must have been a Hun which had been bombing England… At last, through the wecome beam of an enemy searchlight, we identified it as a Dornier 17. Moreover, both pilots on board seemed very happy, they had their full cockpit lights on…
   In the rear both my bottom and top guns slid slowly over to the starboard side and I told Mac to take careful aim. Then counted slowly.
“one – two – Three,” and then yelled “Let him have it Mac!”
There was a quick staccato roar as all four guns belched out tracers and the Dornier dived to the ground with one engine on fire. (4)

   In the period of April-December 1940 it is estimated that 1243 mines had been laid of which 765 were laid by Bomber Command. At the time it was believed that fifty ships measuring 108,860 tons. Post War it was revealed by Lloyds that the figure was a lot higher standing at 120 ships measuring 111,163 tons were lost with a further eleven worth 31,190 tons, damaged by every type of mine. Of the aerial mines it is estimated that 86 ships, worth 82,983 tons, were sunk and a further ten (17,070 tons) were damaged with around half of those being sunk by mines laid by the Hampdens in the Kattogat Belts and western reaches of the Baltic. In the period between April and November 1940 only XX Hampdens had been lost on Gardening operations proving to be the safest operational sortie they carried out in the year.

   There was a small descrepency with the original Air Staff Memorandum (no. 60) giving credit to Bomber Command for sinking four ships off the Dutch Islands which were in fact mined by Coastal Command who exclusively mined the Dutch, Belgian and French coasts and the Hampdens covering Brest, Germany and the Baltic.

   On 10 January Bomber Command instructed 5 Group that Gardening missions were only to be used for training their crews for night operations and navigation which would release experienced men for more essential Oil operations over Germany. As a gesture they did offer that on nights that they were not able to conduct bombing missions that they would release fifteen aircraft with trained crews. On the 25 January this was ratified with Gardening missions only to be undertaken at the C-in-C’s discretion for the training of fresh crews, by Stirlings and Manchesters as part of the Squadron’s conversion process and trained Hampden crews when the weather over Germany precluded bombing operations. This left Bomber command with only the Oil targets in German y and the possibility of invasion ports and vessels on the specific instruction of the Air Ministry.

   Coastal Command were concerned at the idea of untrained crews now carrying out their vital work and out of this concern they pressed for one Hampden Squadron to be permenantly be assigned to their Command. It was an understandable concern as simple mistakes could be made which could invalidate the whole mission. Sgt Peter McDermott of 61 Squadron recalled his first flight;
We were caught in searchlights and flak started to burst around us as I set course on our timed run of exactly forty six seconds. “One, two, three” intoned Staff as the flak continued to rattle on the fuselage. He got to about twenty when he said “I’m not sure of the count, Skip, we had better go back and start again.” Came the roar from the experienced Les Boot “Carry on, it’s twenty nine, thirty,”… On “Forty-six taken up again by the navigator we dropped our mine. Euphoria We had struck our first blow against the Reich. (5)

   In a communique to the Air Ministry on 13 February, Coastal Command expressed this concern especially pointing out that with Bomber Command no longer operating there would be no mines laid east of the Elbe which was where they were causing the most damage and were causing problems for the Kriegsmarine’s larger vessels and it was further questioned as to whether they would be able to reach the Admiralty’s proposed quota. The Director of Naval Co-operation concurred and pressed for Bomber Command to step up its effort rather than scale back.

   The Air Ministry however did not agree due to the more pressing issues faced by Bomber Command and declined the request for a Hampden Squadron and that Bomber Command’s directive would stand but assured Air Marshal Bowhill, the C-in-C of Coastal Command on the 5 March that they would be reviewing the situation regularly.

   Operations at the beginning of 1941 had already been sluggish and hampered by bad weather and with the removal of the Hampdens only Coastal Command’s Beauforts and Swordfish of the Fleet Air Arm but despite hard work they were unable to get anywhere near the Admiralty’s quota. A back and forth for solutions was passed between the Admiralty and Coastal Command with final approval for the riskier daylight operations and the even riskier dropping mines in front of convoys as they cruised down the coast. It was a dangerous manoeuvre which had been carried out with a modicum of success on 22 April.

   By 4 April Bomber Command were back in the frame for further mining operations with the Admiralty keen to deploy Gardens to stop invasion if Seelöwe looked iminant with the ports from the Ems to Brest as possible targets as well as coastal convoy routes. Such a task was well beyond the airforces already available and due to the nature of the emergency and anti-invasion raid meant that Bomber Command would need to prioritise it. This Air Ministry considered that mining the fleet of barges would have more success than actually bombing them in “some cases” 6  and anti-invasion measures were in Bomber Command’s remit of aims outlined in January.

   The notion of high altitude drops as a used by the Luftwaffe were discussed as a principle by the Air Ministry on the 1 May. The German mines were designed to explode if they struck land but act as magnetic mines if in water. The Admiralty had noted the amount of extra precautions they were having to take to watch for these attacks on ports and slim channels and were hoping to do the same to the Germans. The Air Ministry were satisfied that their equipment could carry out the task without modification but they were concerned about the accuracy of the drops from 12,000 feet let alone doing it whilst under fire from heavy flak emplacements around ports and estuaries at night as well as raising the question of how severe would their casualties be? Coastal Command were also worried that as British mines would not explode if they hit the ground it might mean that they would be recoverable by the enemy but the Admiralty dismissed this concern saying that the Germans had more than likely already recovered the mines and cracked their operating system. The Admiralty believed that Brest Harbour was already a small target and expected inaccuracies though the Air Ministry believed that from the minimum height of 10,000 feet would lead to a fifty percent accuracy which would not be worth the losses that would likely be incurred. Bomber Command concurred although believed 12,000 feet was the minimum height and would prefer a mine without a drogue or parachute. There was also a strong move to develop a mine similar to the German model that acted as a bomb and at a conference on 1 July 1941 it was agreed to start to develop such a mine.

   The campagn through 1941 was carried out by Coastal Command’s Beauforts and the Fleet Air Arm’s Swordfish causing significant damage to the German shipping including the Sardinen which had to be beached to avoid sinking, a trawler was lost and an 8000 tonne tanker damage causing the Haugesund to be closed for five days and convoys diverted to the west of Farmoy island. The Admiralty had also encouraged a campaign from Jade-Weser to Huibert Gat and to interdict the heavy traffic between the Elbe and waters of Terschelling which allowed crews to defer to a more general target zone if enemy resistance was too stiff over a specific target zone.

   By April until June Coastal Command were concentrating their efforts on the French invasion ports and especially Brest where the Battle cruisers Scharnhorst and Gneisenau were anchored following Operation Berlin and joined by the cruiser Prinz Eugen following her aborted sortie with the Bismarck.

   Following the 15 March Bomber Command moved away from the Oil plan to deal directly with the threat posed by the Kriegsmarine in the Battle of the Atlantic with their aircraft engaging in bombing raids on Brest and along the French and German coasts including assisting in minelaying. On the 8 April six Hampdens of 44 Squadron laid four mines at Calais and bombed a submarine building for the loss of P/O Garley’s Hampden but the nature of the Bomber’s changing role meant these raids were intermittent with raids also directed towards Berlin the following night and Bordeux the day after that!

   By the end of June 1941 the two commands had laid 708 mines with Bomber command laying 507 of them, mostly around Brest and the Bay of Biscay where the Germans had established the U-Boatwaffe. In the first six months of 1941 the Aerial Sea mines had claimed seventeen vessels (23,604 tonnes) and a further six (8351 tonnes) damaged giving the overall number of ships sunk as 103 (106,587 tonnes) and sixteen (25,421 tonnes) damaged for the loss of fifty eight aircraft, forty one of them Hampdens. The most successful month was September 1940 when sixteen vessels (14,448 tonnes) were sunk.

   Gardening would continue and was seen as very successful with limited losses but they would now become part of Bomber Command’s overall offensive against Hitler’s Navy.

1.            IWM Sound archive number  Maurice Strefton

2.            Official History Vol II p. 332

3.            Official History Vol II p. 334

4.            G. Gibson Enemy Coast ahead p.104

5.            M. Postelthwaite “Hampden squadrons of World War II: in Focus” p.38

6.            Official History Vol II p. 338