The War Illustrated No 31 Vol 2 April 5th 1940

The 1 Far Illustrated April 5th, 1910 The Magnetic Mine is Defeated “Hitler’s secret weapon,” as the magnetic mine was nicknamed, was not secret for long neither was it long before counter-measures were devised. Here we have an account by Mr. N . G .Tipples of the “de-Gaussing” process, whose existence was recently announced. During the past few weeks many British ships have been fitted with a special device which renders them immune from damage by magnetic mines, and with the arrival in New York on March 7 of the liner “Queen Elizabeth,” with her giant hull girdled by an anti-magnetic cable, the news of the device has been officially released. A detailed description of it cannot yet be given, as it is still more lessor an official secret, but the broad principle upon which the device works can be found in any text book on electricity and magnetism. Technically it is known as de-Gaussing, because it is based on a law discovered by a German scientist named Gauss, who died about a century ago. Gauss’s Law states that “the number of lines of magnetic induction crossing any closed surface surrounding a magnetic pole of strength isM equal to 4t tM,” but as this will convey very little to the average reader, I shall try to explain the working of this clever device in everyday language, avoiding technical terms as far as possible. First of all, here are a few facts about the magnetic mine itself. Many people are under the impression that the mag­netic mine is attracted bodily upwards by the magnetic pull of the ship as it passes overhead. That idea is wrong. This is what happens when a ship overpasses a magnetic mine :the magnetic lines of force which surround such a huge mass of iron or steel outreach and attract upwards one end of a pivoted magnetic needle, which is the chief feature of the mine’s mechanism. Down goes the other end of the needle, thus closing an electric circuit and detonating the explosives. That is the principle on which the magnetic mine operates, but actually it is not quite as straightforward as that, and an engineer who was able to inspect one aptly described it as“ a devil’s brew of delicate magnetic relays.” The pear-shaped aluminium casing of the mine contains about 1,500 lb. of very high explosive, and the force of this exploding underwater alike depth-charge is quite sufficient to sink or damage severely any unprotected merchant ship. Fortunately this type of mine can only be used ineffectively shallow waters. So much for the mine itself, and now we are in abetter position to understand The defeat of the Nazi murder mine has been accomplished already. In the diagram (left) is shown how the earth’s magnetic field induces a magnetic effect in the hull of a ship. It is this magnetic field of the ship which disturbs the detonating mechanism of the mine with such fatal results. On the right is shown the de-Gaussing coil which neutralizes the ship’s magnetic effect, thus rendering her quite safe from magnetic mines. Above is illus­trated the method of attaching the coil inside the bulwarks of a collier. Specially drawn for TheW aii I l lust rated by Haworth. Photo, Centra! I'ress
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