Further, be it remembered that under quite modern conditions the accuracy of the howitzer fire against the fort can be checked by aeroplanes circulating above the fort, whereas the fort is a poor starting-place for corresponding aeroplanes to discover the howitzer. But while the howitzer has this advantage, it has the grave disadvantage of not having anything like the same range as the gun, size for size. For a great many years it has been known that the howitzer has the advantage I have named. But, in spite of that, permanent fortification was built and could stand, for it was impossible to move howitzers of more than a certain small size. The explosives in those small shells did very great damage, but the fortress could, with its very heavy guns, keep the enemy out of range. But when large, and at the same time mobile howitzers were constructed which, though they fired shells of a quarter of a ton and more, could go along almost over any ground and be fired from almost anywhere, and moved at comparatively short notice from one place to another, it was another matter. The howitzer became dangerous to the fortress. When to this was added the new power of the high explosives, it became fatal to the fortress. To-day the 11-inch howitzer, with a range of about six miles, capable of hiding behind any elevation and not to be discovered by any gun within the fortress, and, further, capable of being moved at a moment’s notice if it is discovered, has the fortress at its mercy. Air reconnaissance directs the fire, and great masses of high explosives can be dropped, without serious danger to the besieger, upon the fortified permanent points, which are unable to elude great shells of high explosive once the range has been found. Another development of the present war, and somewhat an unexpected one, has been the effect of the machine-gun, and this has depended as much upon the new German way of handling it behind a screen of infantry, which opened to give the machine-gun play, as to any other cause.