Thread: German Magnetic Mine

On the night of November 27, 1939 artillerymen at Shoeburyness saw a German seaplane dropping parachute mines on the foreshore. A naval officer and a photographer followed the retreating tide until near enough to take flash-light photographs.
Experts from the Portsmouth Mining School arrived 6 hours afterwards, and then began the heroic work which, as .Mr. Churchill said, “reads like a detective story." Five men, Lt.-Cdr. J.G.D. Ouvry, Lt.-Cdr. R Lewis, Lieut. J. Glenny, C.P.O. C. Baldwin (later killed while in service), and A.B. A. Kearncombe, set about the dangerous task which might well cost them their lives, but would, if successful, reveal the secret of the Nazi magnetic mine. First they anchored the mine and then made pencil and paper rubbings, of the external fittings, and whilst waiting for the next low tide special tools were improvised of non-magnetic material. Lt.-Cdr J G. D. Ouvry undertook to make the first operations. He told the rest of the party which fitting he was going to start working on and the sequence of his procedures. Thus, if the mine should happen to blow him up, the others would beware of that fitting when dealing with other mines. He removed the fitting in safety, and it appeared to be the detonator. So the whole party got to work on the other fittings. One by one they removed them, and then came a nasty shock when they discovered a second detonator
Twelve hours after they had arrived to make their investigation of this latest example of the Nazis ingenuity in devilish invention, they had sent the mine on its way to Portsmouth, harmless and with its secrets laid open before the experts.

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The first German magnetic mine before being rendered safe. Shoeburyness, 23rd November 1939.

After Decorating the Five men who solved the “Magnetic Mine Mystery” His Majesty along with Lt-Cdr Ouvry, inspects the Mine at H.M.S Vernon Mine and Torpedo School at Portsmouth.

Loading the mine into a lorry after rendering it safe. Left to Right. A.B. Vearncombe. Lt-Co Lewis, C.P.O. Baldwin, and Lt-Co Ourvy with bact to the camera.

Hitler boasted of a "secret weapon" which would sink our ships and leave us guessing. The story below was written in 1943 of how a small party of R.N. personnel tackled this serious challenge is here told in full for the first time by Lieut. Commander John G. D. Ouvry, D.S.O., R.N., of H.M.S. Vernon. He received his decoration for the part he played on that occasion. Lieut. Commander R C .. Lewis, R.N., also was awarded the D.S.O., and Chief Petty Officer Baldwin and Able Seaman Vearncombe the D.S.M:

On September 10, 1939 seven days after the outbreak of war the steam vessel Magdepur was sunk in low water off Orford Ness. The casualty was attributed to an enemy mine, and minesweepers stationed at Harwich were sent out to clear that area. For hours they swept, but no mines were forthcoming. Later, another vessel was seriously damaged by a mysterious explosion while passing down, the same channel. A significant fact came to light. The hull of this ship had not been pierced, yet the underwater explosion had been severe enough to put her machinery out of action. This suggested to the experts that a non contact type of mine-magnetic, or acoustic, or actuated by some other means was being used by the enemy. Casualties continued to occur round our coasts, usually at the entrance to big ports. By the first week of November it was apparent to the authorities that if the Germans could lay this mine in sufficient numbers in our seaways the result to this country would indeed be serious. On the night of November 21, 1939 German aircraft flew up the Thames and other estuaries, dropping into the water long cylindrical objects attached to parachutes. This, then, was the Nazis method, or one of their methods of depositing their infernal "secret weapon," As one of the staff of the Mines Department of H,M.S. Vernon (the R.N. Torpedo and Mining School) I was awakened at 3 am the following day and instructed to catch the first available train from Portsmouth to London, I went direct to the Admiralty, where I was informed that I was required to remain at immediate notice to endeavour to discover the type and mechanism of these mines, Speed in this task was of the very greatest importance, for our sea traffic was in danger of being brought to a standstill.

Late that night, tired out with the strain of hours of waiting, I went to a London hotel to sleep. I was wakened soon after midnight to receive an urgent message from the Admiralty instructing me to return there at once. I did so, and met Lieut. Commander Roger Lewis, R.N. He told me that aircraft had again flown over the Thames estuary that night and had dropped an object, probably a mine off Shoeburyness. Low-water there was at 4.30 am, and it was likely that the mine would then be exposed.

Our orders were to locate it, attempt to render it safe; then collect it for further investigation at the Mine Experimental Department of H.M.S. Vernon, at Portsmouth. We went by fast car to Southend, through the darkness and the rain. At Southend we joined up with Commander Bowles, R.N., on the staff of the Naval Officer in Charge, Southend. We continued our journey to Shoeburyness, where Commander Maton (attached to the Experimental Department), who was to provide guides and all facilities, had already collected a small party of helpers. Together we headed seaward, filled with excited anticipation. Guided by torches, we slithered for about 500 yards over slimy mud and sand. Occasionally we splashed knee deep through pools. We strained our eyes in the darkness. Suddenly one of the guides, a, private soldier who had seen the airborne object drop into the water in the early hours of the night, shouted, "There it is, sir!" It was a very thrilling moment when the light from the torches, concentrated in the direction he indicated, revealed a glistening object with horns. It was our intention to carry out a preliminary examination, take flashlight photographs, then lash the mine down until the daylight low-water period, when we would do our best to render it safe. Lewis and I, having divested ourselves of metal items likely to influence the mechanism of the mine, approached it, leaving the remainder of the party in the rear. The external fittings of the aluminium alloy cylinder (it was seven, feet long and 26 inches in diameter) were secured by screw rings requiring a special type of pin-spanner to remove them. We took paper rubbings to serve as patterns from which suitable tools (of non-magnetic metal) could be fashioned.

H.M. The King listens to Lt. Cdr. Ouvry’s description as he inspects the German magnetic mine. Hitler’s “secret weapon” bore the date 1938.

If We Were Unlucky

Having lashed the mine securely and obtained our flashlight photographs, we set off back to our quarters. Confirmation that we really had found what we had been sent to look for came with the discovery of a parachute stretched out on the mud, a parachute fitted with an automatic release device which came into operation after the mine had entered the water. Lieut. Cmdr. Lewis and I had a very early breakfast, but it was not until early afternoon that the state of the tide permitted us to return to the scene of operations. Petty Officer Baldwin and Able Seaman Vearncombe, who had been with me on previous expeditions, had now arrived from Portsmouth, and soldiers with a caterpillar tractor waited inshore to cart off the mine as soon as we had finished.

We decided that Chief Petty Officer Baldwin and I should endeavour to remove the vital fittings; Lieut. Cmdr. Lewis and Able Seaman Vearncombe to watch from what we considered to be a safe distance and make detailed notes of our actions and progress for reference in case of accident. There was a possibility that the mine had devices other than the magnetic one, which added to the hazard. If we were unlucky, the notes which the two watchers had taken would be available for those who would have to deal with the next available specimen. I first tackled an aluminium fitting sealed with tallow. In, order to use one of the special spanners which had been rushed through (by Cmdr. Maton) in the local workshops for us, it was necessary to bend clear a small strip of copper. That done, we were able to extract this first fitting. Screwed into its base, when we drew it clear, we found a small cylinder obviously a detonator, for in the recess from which the fitting had been withdrawn were disks of explosive. These I removed. This mysterious fitting proved to be a delay bomb fuse, it was necessary for the airman to tear off the copper strip referred to (before releasing his load) if bomb not mine was the requirement.

Before we could proceed further we had to call on Lieut. Cmdr. Lewis, and A.B. Vearncombe for assistance to roll the mine over this being firmly embedded in the hard sand and held fast by the tubular horns. The fact that the mine did not, and was not intended to float explains the non success of our minesweepers in their efforts to secure a specimen. Lieut. Cmdr. Lewis and A.B. Vearncombe from then onwards lent a hand with the stripping down. Dr. Wood, Chief Scientist of the Mine Design Department, H.M.S. Vernon arrived in time to witness the later stages. We were somewhat startled to discover yet another detonator and priming charge. Having removed all the external fittings, we signalled for the caterpillar tractor and soon had the mine ashore. We had a shock and a laugh when the shock wore off before we had stowed away all the removed gadgets. We stopped for a breather on the foreshore, and one of the helpers carrying a rather heavy fitting put it down on a stone. It immediately commenced to tick noisily. The company dispersed like lightning! That most disturbing ticking, we presently discovered came from clockwork mechanism within the heavy fitting actuated by pressure, it happened to rest on its starting spindle. This proved to be a delay action device, designed to keep the mine safe until the clock setting had run off. Next day the body of the mine and the components we had removed were sent to H.M.S. Vernon. When we arrived there we were conscious of a somewhat tense atmosphere. The complete specimen had been locked up in a laboratory outside which stood a sentry with fixed bayonet. Responsibility for further investigation, searching of the actual interior now passed to Dr. Wood, and his two assistants, Mr. W. F. B. Shaw and Mr. H. W. K. Kelly. These experts worked on into the night, until they had laid bare the final secret of this destructive device. They found in the mines interior an intricate and beautifully made piece of electromagnetic apparatus, this actuated by the passage above it of a steel hull, would fire a detonator which in turn would "set off" the 660 lb of high explosive packed into the forepart of the 1,130 lb mine. It was not long before a counter-measure was devised, our metal hulled ships were fitted with degaussing coils anti-magnetic cables which rendered Hitler’s "secret weapon" innocuous.

There was a good documentary on History Channel not long back about this. Saved countless lives with the countermeasures developed from the first one they actually got hold of.