By July 27, 1918, the Franco-American forces had driven the Germans almost entirely out of the wooded area they had been so obstinately defending. The pressure was constantly maintained toward the road junction of Fère-en-Tardenois, the Franco-American objective, and thither the pursuers progressed through the remainder of the dense woods and over rain-soaked fields and hills on their outskirts. In the course of this forest fighting the troops were warned to watch for Germans wearing American or French uniforms, a device they had successfully practiced. Rushing across an open place in the forest when German nests had been discovered, a German, speaking perfect English, called to American machine gunners: "Don't shoot. There are Americans in that thicket." The Americans were at the edge of the forest, firing into a wood opposite. They ceased when the detachment appeared. The detachment entered a forest to the right of the Americans, and in a few minutes a hail of machine-gun bullets came from that direction. The Americans realized that they had been duped, and turned their machine guns upon the impostors. On July 28, 1918, the Americans were on the south bank of the Ourcq. This river, intended by the Germans to be a halting line, but which they could not hold, marked a notable point in the American progress from the banks of the Marne. Foch's forward movement from the west and southwest had been proceeding simultaneously and now became merged along this river into the movement up from the south. American participation from the west had been less conspicuous; but American troops left their mark, whatever their zone of operations, and in this area they made their presence painfully felt south of Soissons. At the beginning of the western advance, east of Vierzy and northeast of Chaudon, they encountered the pick of the German shock troops after fighting for thirty hours. The result was that the youthful Americans, meeting the kaiser's best, who were fresh and in the pink of condition, themselves essayed the task of becoming shock troops. They had reached their objectives, a varying number of miles eastward, and were consolidating their positions when the shock came. Against one American unit two German shock divisions were hurled; against another came the famous Prussian Guards. The Germans had machine guns mounted on wheels and rolled them to the edge of the woods where the fighting occurred. These guns shot explosive bullets at the Americans. Shock troops came to close grips with shock troops--and the Franco-American advance was not only sustained but extended. CHAPTER LVII SERGY AND SERINGES