April 5th, 1940 The War Illustrated 351 How the Nazi Murder Mines Are Made Harmless On the left, part of the actuating mechanism of amine is being examined and tested by a British naval officer. Although far from simple in design, it is of robust construction. The enormous and devastating effect of 1,500 pounds of high explosive can be judged from the photograph on the right. This was taken when amine which could not be dismantled safely was deliberately detonated. In the case of ordinary mines this is accomDtished by rifle fire oran electric detonator. Photos, Planet News something of the measures which have been taken to defeat this menace. The mass of andiron steel which constitutes a ship’s hull is really a powerful natural magnet, due to the unseen but nevertheless insistent effect of the earth’s magnetic field. One end of the vessel will have north polarity and the other end south polarity. By using an instrument known as a magnetometer and by applying Gauss’s Law an expert can calculate to a fine degree the disposition and strengths of the magnetic poles which exist in the hull of the ship. He is then able to design an electro-magnet which will create a magnetic effect equal in strength but opposite in polarity to the natural magnetism of the ship. In practice this electro-magnet takes the form of a number of turns of heavily insulated cable coiled around the entire length of hull high above the waterline. The length of cable used in such an anti-m agnetic belt may total as much as ten miles in the case of a big ship. The cable is supported a t intervals of about afoot by metal brackets, which are welded high up 011 the ship’s side. The ends of the coil are connected up to the ship’s dynamo and an electric current of a predetermined strength is forced through it. Then magnetic lines of force outspread and neutralize the ship’s magnetic field, and that is why a ship which has been de-Gaussed in the above manner can safely sail over a magnetic mine without disturbing that deadly needle. I t maybe outpointed that vessels which have been fitted with this apparatus have to make two compass adjustments :one for when the apparatus is not in use, and another for when the de-magnetizing current is switched 011. At the ship's generator controls, the chief engineer of a collier connects the de-Gaussing coil to the dynamo. The ship is now safe from magnetic mines. Photo, Central I’rcss When dealing with amine that might be of the magnetic type it is essential not to be wearing anything metallic. Keys, penknife, cigarette case, and even a greatcoat with brass buttons (left) were discarded by the Lieutenant-Commander of the Rendering Safe of Mines Squad before he approached a stranded mine. However, once the detonating mechanism has been removed ordinary tools maybe used. The man on the right is seen dismantling the switch mechanism on the base-plate of a stranded contact mine.