When one has seen ten 15-inch shells strike a town of 25,000 inhabitants in a busy hour of the day and only half a dozen persons killed and injured, he may learn a contempt for shell fire which, however, is promptly turned into a tragic respect when one of the same sort of shells strikes in a stone-paved courtyard where a hundred soldiers are at their evening meal, and two-thirds of them are killed and wounded. The bursting of a shrapnel shell and its spray of low-velocity bullets is also theoretically most destructive, but a roof of 6-inch boards will furnish perfect protection from the bullets. Mother Earth remains the best protection there is from fire. No rifle bullet can penetrate through a 3-foot thickness of sandbags. A 6 or 8-inch high-explosive shell, which is the largest caliber practicable for trench warfare, may burst near a double layer of bags of stone rubble without hurting anyone in a cellar 30 feet underneath. The rain of shrapnel bullets which mows the barbed wire in front of a trench, as hail mows ripening grain, will not reach a single man in the trench to the rear, if he keeps his head down. At first thought it seems utterly inconsistent when bullets carry effectively a mile and a half, and guns carry twenty miles, that infantry should be fighting so close that they can throw bombs at each other from distances of 15 and 20 yards. The very destructiveness of modern weapons has contributed toward this result. There has never been anything like so many guns used in battle, and never have they been capable of such rapid fire. The field gun can fire consistently eight or ten shots a minute, thanks to its modern recoil cylinder and to the steadiness of aim, and literally establish a "curtain of fire" with its torrent of bullets shot down from the air and the cataracts of earth shot up by the bursting of high-explosive shells in the ground, which no infantry can pass. A machine gun behind a shield firing 500 shots a minute is practically safe from rifle fire, and soldiers intrenched on either side of it add to its volume their own more accurate fire from their rifles. Infantry in the open, though they were not subjected to the fearful concentration of artillery fire, could not survive through a mile of machine-gun and rifle-swept space. Successful advances against anything but very inferior numbers badly armed become impossible in any frontal attack in the open. Thus all modern infantry operations must have more or less a siege character, as the only practicable means of approach is by digging your way forward. The spade has become almost as important a weapon as the rifle.