The Allies had learned the lesson of the futile offensives of 1915, and of the long-drawn contest at Verdun. They no longer dreamed of breaking the enemy’s front by a sudden bound, for they realized the depth of his fortified zone. They had accepted the principle that an attack should proceed by stages, with, as a preliminary to each, an elaborate artillery “preparation;” and they realized, too, that, since the struggle must be protracted, fresh troops must be used for each stage. Their new plan was simply attrition on a colossal scale. It was like the mighty head of water which hydraulic engineers apply to a mountain in order to wash it away. The governing idea was not a breach in the front, though that might come incidentally, but such a steady, unrelenting pressure as would first cripple and then destroy the enemy’s machine. Their method was that of “limited objectives,” with new troops and a new bombardment for each phase, and they had certain tactical devices in reserve which they hoped to apply with good effect at the right moment. To quote what I have written elsewhere, the scheme might be suggested by the metaphor of a sea-dyke of stone in a flat country where all stone must be imported. “The waters crumble the wall in one section, and the free reserves of stone are used to strengthen that part. But the crumbling goes on, and to fill the breach stones are brought from other sections of the dyke. Some day there must come an hour when the sea will wash through the old breach, and a great length of the weakened dyke will follow in the cataclysm.” This method of attrition presupposed the continuance of the war on two fronts. When Russia fell out of line the situation was utterly changed, and the plan became futile against an enemy with a large new reservoir of recruitment. But at the time of its inception, uninspired and expensive as it was, it was a sound plan, and _ceteris paribus_ would have given the Allies victory before the end of 1917. Even as things turned out, in spite of the unlooked-for _débâcle_ in the East, the Battle of the Somme struck a blow at the heart of Germany’s strength from which she never wholly recovered.