Magnetic flux-deviation detector, with integrated events counter, deployed in a German naval (magnetic) mine, of 1939-1945


Magnetic naval-mine discriminator with integrated events counter

When a ship, representing a metal body, is passing not too far from the two metal poles (rods) of this device, its magnetic equilibrium (balance) is becoming disturbed and the system is being triggered. The figure 20X indicates, that this device initially should not being ignited (explode) before it had been triggered for 19 more occasions to come. Hence, several ships could have been passing the spot, without anything happening, one easily could have trusted that the passage is save (not being corrupted). The number indicated, only explains that the mechanical counter is able to count up to maximally 20 events, though, is not necessarily the figure that actually could have been pre-set for. The symbols 'bnc'* indicates that this unit had been manufactured after say mid 1942, as these kinds of manufacturer-codes was initiated after the British "Bruneval Raid" of February 1942. Since, generally, the German type number-plates were removed and being replaced by a kind of 'stickers'. German wartime plates carried often rather interesting information. In contrast, Allied (nomenclature) plates did pass, generally, type-information that did not directly make sense. This is why the Germans preferred to deploy (system) code-names like: Lichtenstein, Würzburg, or when particular modules were involved, like - Igel, Zobel, Grille, Saturn, Jupiter, Nashorn, though also Naxos, Berlin, Freya, Ehrenmal  ... and so forth

* Vereinigte Maschinen, Kessel u. Waggon Fabrik, L. Zielenienski u. Fitzner Camper A.G. Werk Krakau (General Gouvernement, now  again Poland); The details on this manufacturer is changed, maybe already during the war in: Zieleniewski, Maschinen- u. Waggonbau, Krakau G.m.b.H. What the reason was is not known, maybe this company came under a German "Verwalter" (Trustee). Or, one (or both) of the owners was Jewish?


M is pointing towards a small mirror, which might have been used for testing purposes, as to prove that the magnetic flux-deviation-mechanism is functioning appropriately; without having the danger of activating the lethal counter-mechanism electro-mechanically



The number of actual events (presetting) before this naval mine initially is being ignited, is (probably) set by the pointer adjusted between 2 and 14. The electromagnetic coil just below the number-scale is to trigger (stepping-up) the electro-mechanical (counter) mechanism. The grips of the number disk-ring, might also been used to winding-up a loaded spring somewhere inside it, as to drive the motion (motion) of the system


The green-grey metal block in the centre, might be of a non magnetic nature (non-Ferro), as this would otherwise by-pass, or disturb, the magnetic flux somewhere in between both metal poles (rods) (diameter of 20 mm). When we take in to account the second photo of this series, the mirror-mechanism must have been pivoted somewhere in between the gap of the two metallic poles. The mirror-mechanism is also mechanically connected onto a sensitive switching arrangement, which is initiating the triggering steps (process)


Just in the upper section of the mechanism, we see a hair like electrical wire fixed between two brass strips. I don't know whether this is to trigger the main ignition, or that it is meant for another stage of the initial process. When we look carefully, we can also notice that the wire fixed between the two brass strips just above the Bakelite covering-disk is blown (left hand-side open), which might indicate that some action was already initiated. This kind of electromagnetic detector is only functioning as long as there is enough battery power available. I myself have no idea how long  a sufficient battery-charge actually might have lasted. When Nc types were involved, this could have been lasted for quite some time, we must then think in terms of years. The discharging of a Pb battery is, however, rather considerable and we then have to think, I guess, of maximally one year


I received an e-mail on 11 April 2010 from a French enthusiast that he found a photo of the same device on the Austrian Eumig company page:    The device shown half way the page definitely is such a device. The text is, however, quite fuzzy about whether they have designed the device themselves or that they had been involved in reproducing such devices. The actual company in Krakau most likely is not the kind of firm to develop such kind of apparatus.

On 20 May 2014 I received another e-mail:

Dear Mr. Bauer,


i have compared the photo on your website and the photo and text on the linked page „“ from Eumig (Vienna). It is interesting to compare the letters „bnc“ on your photo and the letters „bno“ on the Eumig site. It seems the it is on both photos the letters „bno“ and not „bnc“ as the „c“ seems to be a scratched „o“ as the letter „c“ should have a wider opening on the right side.


Also the Eumig site states almost clearly that Eumig was only manufacturing the devices, as the finest screws Eumig processed so far were M3, and the flux detector had much finer screws. So they could  benefit from this manufacturing. And the finished devices were delivered in wooden boxes marked with „bno“ for Eumig in Vienna. This is at least what the text says.

 So to my conclusion, the device depicted on your site is most probably a device manufactured at Eumig in Vienna and marked with „bno“ therefore.

 Best regards from Vienna and many thanks for your exceptional work,

 Gerald Hodatsch (OE1HGA)



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