The English 12-inch (Mark IX.) gun consists of a steel tube, wound practically from end to end with layer after layer of steel ribbon or wire of very great tensile strength. This tube is known as the A tube, and may be called the hollow heart of the gun. As much as a hundred miles of wire will be used for one of these guns, and, of course, for the newest guns, the 13-inch weapons, such as have been placed in the latest super-_Dreadnoughts_, or the 15-inch guns which it is said will be placed in the _Dreadnoughts_ of 1912 or the year after, the amount is a great deal more. The greatest thickness of layers is placed round the breech of the gun, where the strain is most severe, and each succeeding layer is wound on with increasing tension, though to the ordinary observer the first layer seems to fit so tightly that nothing could be tighter; but the gun makers know better. All along the chase or fore part of the tube another tube, called the B tube, is shrunk on to ensure that it shall be the tightest fit possible. Then, over a portion of the B tube, and also over a portion of the winding, that part of the gun known as the breech jacket is shrunk. Apparently everything is so strongly fixed together that nothing can cause the parts to separate, but the gun makers know this is not so, for into this jacket a bush is screwed to prevent any movement of the A tube, so far as the jacket is concerned. The A tube itself contains a thin steel inner tube inserted from the breech and fixed in position by the breech bush. It is this inmost tube which has to bear the wear and tear caused by the firing, and suffers from erosion, due to the gases generated by the explosion of the charges, and has to be replaced by a new tube when it is no longer fit for service. [Illustration: THE 12-INCH GUNS OF H.M.S. “NEPTUNE.” _Photograph by Stephen Cribb, Southsea._] Gun makers have always responded cheerfully to the challenge to penetrate the hardest armour of the time, and have succeeded in producing weapons which are able to penetrate any armour now carried. The problem at present is to increase the range at which the penetrative power may be exercised. This can only be attained by the increase in the length of the gun and the use of explosives developing higher pressures in order to obtain higher velocities. The British gun of 45 calibres and 9.2 inches diameter is about to be superseded by one of 50 calibres, and the 40-calibre gun carried in some of the latest ships is being superseded by the 12-inch gun of 45 calibres. Twelve-inch guns of 45 calibres and 10-inch guns of 50 calibres have been installed in the new ships, built at Elswick recently, for the navies of Japan and one of the South American States.