The preparation for a complicated operation against the formidable defenses in front of us included the assembling of divisions and of corps and army artillery, transport, aircraft, tanks, ambulances, the location of hospitals, and the molding together of all of the elements of a great modern army with its own railheads, supplied directly by our own Service of Supply. The concentration for this operation, which was to be a surprise, involved the movement, mostly at night, of approximately 600,000 troops, and required for its success the most careful attention to every detail. The French were generous in giving us assistance in corps and army artillery, with its personnel, and we were confident from the start of our superiority over the enemy in guns of all calibers. Our heavy guns were able to reach Metz and to interfere seriously with German rail movements. The French Independent Air Force was placed under my command which, together with the British bombing squadrons and our air forces, gave us the largest assembly of aviation that had ever been engaged in one operation on the western front. LOCATION OF THE TROOPS. From Les Eparges around the nose of the salient at St. Mihiel to the Moselle River the line was roughly forty miles long and situated on commanding ground greatly strengthened by artificial defenses. Our First Corps (Eighty-second, Ninetieth, Fifth, and Second Divisions), under command of Maj. Gen. Hunter Liggett, restrung its right on Pont-a-Mouson, with its left joining our Third Corps (the Eighty-ninth, Forty-second, and First Divisions), under Maj. Gen. Joseph T. Dickman, in line to Xivray, were to swing in toward Vigneulles on the pivot of the Moselle River for the initial assault. From Xivray to Mouilly the Second Colonial French Corps was in line in the center and our Fifth Corps, under command of Maj. Gen. George H. Cameron, with our Twenty-sixth Division and a French division at the western base of the salient, were to attack three difficult hills--Les Eparges, Combres, and Amaramthe. Our First Corps had in reserve the Seventy-eighth Division, our Fourth Corps the Third Division, and our First Army the Thirty-fifth and Ninety-first Divisions, with the Eightieth and Thirty-third available. It should be understood that our corps organizations are very elastic, and that we have at no time had permanent assignments of divisions to corps. MOVEMENT OF THE TROOPS.