After four hours' artillery preparation, the seven American divisions in the front line advanced at 5 A.M. on September 12, assisted by a limited number of tanks manned partly by Americans and partly by the French. These divisions, accompanied by groups of wire cutters and others armed with bangalore torpedoes, went through the successive bands of barbed wire that protected the enemy's front line and support trenches, in irresistible waves on schedule time, breaking down all defense of an enemy demoralized by the great volume of our artillery fire and our sudden approach out of the fog. Our First Corps advanced to Thiaucourt, while our Fourth Corps curved back to the southwest through Nonsard. The Second Colonial French Corps made the slight advance required of it on very difficult ground, and the Fifth Corps took its three ridges and repulsed a counter-attack. A rapid march brought reserve regiments of a division of the Fifth Corps into Vigneulles in the early morning, where it linked up with patrols of our Fourth Corps, closing the salient and forming a new line west of Thiaucourt to Vigneulles and beyond Fresnes-en-Woevre. At the cost of only 7,000 casualties, mostly light, we had taken 16,000 prisoners and 443 guns, a great quantity of material, released the inhabitants of many villages from enemy domination, and established our lines in a position to threaten Metz. This signal success of the American First Army in its first offensive was of prime importance. The Allies found they had a formidable army to aid them, and the enemy learned finally that he had one to reckon with. PREPARATION FOR THE ARGONNE OFFENSIVE. On the day after we had taken the St. Mihiel salient, much of our corps and army artillery which had operated at St. Mihiel and our divisions in reserve at other points, were already on the move toward the area back of the line between the Meuse River and the western edge of the forest of Argonne. With the exception of St. Mihiel, the old German front line from Switzerland to the east of Rheims was still intact. In the general attack all along the line, the operation assigned the American army as the hinge of this Allied offensive was directed toward the important railroad communications of the German armies through Mezieres and Sedan. The enemy must hold fast to this part of his lines or the withdrawal of his forces with four years' accumulation of plants and material would be dangerously imperiled.