The primary object of the operations so far had been the capture of Lens. The importance of the place can hardly be over-estimated. If we imagine England with Lancashire and the West Riding in hostile occupation, we shall have a parallel to the case of France deprived of the Department du Nord and part of Pas de Calais, except that in our own case we should still have left to us many manufacturing districts, and France has but few. The importance to the economic life of France of the three towns of Lille, Roubaix and Tourcoing is comparable to the importance of Manchester to us, and the coal-mining districts lying round Lens, which include such fields as those of Courrières, Drocourt and Dourges occupy relatively a far more important position than those of the West Riding. Lens itself is the key to this productive area, whose energies are at least as valuable to the enemy as to its rightful owners, and Lens has in skilful hands become a fortress in the modern sense, far more difficult of capture than older works at one time deemed impregnable. It is comparatively easy to concentrate fire upon guns whose position is known, as they must be when permanently mounted in the fortifications of the text-books, and once a sufficient concentration of fire has been obtained, guns so sited, being incapable of removal, must sooner or later be put out of action, but it is impossible so utterly to destroy a city and its suburbs that its ruins are no longer sufficient to afford cover to mobile ordnance and machine guns. It has been found that a building that in itself is merely a screen from direct observation, becomes, when destroyed by artillery fire, a heap of ruins amongst which may be concealed artillery and machine guns, and which by its very mass is an excellent protection against hostile fire. Bombard this type of fortress as you will, its defenders are not tied by their gun-mountings to any one position, but can move their batteries from place to place, knowing full well that the attackers, with each round they fire, are preparing fresh situations wherein they may be concealed. It will surely be found that this war has sounded the knell of permanently fixed guns except for purposes of coast defence, where alone the immobile gun has triumphed in the face of many years' accumulation of scornful criticism.