The British dismantle their first magnetic mine

The British were struggling to devise counter-measures to the magnetic mine, which was starting to cause significant ship losses. The conventional contact mines were moored close to the surface and exploded when a ship came into contact with the ‘horns’: it was possible to ‘sweep’ for these – cutting the mooring lines and then disposing of the floating mine by gunfire. The magnetic mine just lay on the sea bed and was activated by the change in the magnetic field when a ship passed over it – although the British would not know exactly how it operated until they could get their hands on one. A breakthrough came when German aircraft were seen laying mines by parachute off Shoeburyness, and it was possible to gain access to one at low tide. There remained the problem of actually dismantling it.

The German mine recovered from Thames Estuary near Shoeburyness

Lieutenant-Commander JOHN G. D. OUVRY RN describes how he dealt with the mine:

We decided that Chief Petty Officer Baldwin and I should endeavour to remove the vital fittings; Lieutenant-Commander Lewis and Able Seaman Vearncombe to watch from what was considered to be a safe distance and make detailed notes of our actions and progress for reference in case of accidents. 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 Commander 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we drew it clear we found a small cylinder-obviously a detonator, for in the recess from which the fitting had been withdrawn were disks of explosive.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 action 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 Commander Lewis and Able Seaman Vearncombe for assistance to roll the mine over, this being firmly embedded in the hard sand and held fast by 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. Lieutenant-Commander Lewis and Able Seaman Vearncombe from then onwards lent a hand with the stripping down.

Dr Wood, chief scientist of the Mine Design Department, HMS 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 began 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.

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