Of course, the American troops in France then ready to fight could not alone make up the Allied army of manœuvre. They were the core of it, however, and their growing numbers guaranteed it almost indefinitely, so that the attack of which it was to be the backbone could safely be begun. Some of the troops originally intended for welding with the British and French Armies were kept in the line without change. But in the main the statement was true: the American Army was to rove behind the Allied lines till Foch discovered or divined a German weakness to strike into. In the second battle of the Marne, begun that July 18, when the Allies took the offensive again for the first time in more than a year, the crown prince and his army of approximately half a million were tucked down in the Marne salient, driving for Paris. The German line came down from Soissons to Château-Thierry, ran east from Château-Thierry along the Marne River, then turned up again to Rheims. In a space about thirty miles square the crown prince had imprudently poured all his troops, which, for the fifth offensive, begun July 15, included about a third of the man-power of the western front. The Allied troops lying around the three sides of this salient were French and American on the western side, Americans across the bottom, east from Château-Thierry, and French, British, and Italian from the Marne up to Rheims. While the French and British were squeezing in the two sides at the top, it was the American job to keep the Germans from bursting out from the bottom, and, if possible, to break through or roll them back. The Americans began the attack east of Château-Thierry, where the Germans had crossed the Marne and lay a few miles to the south of it. There had been lesser actions here for several days, in the process of stopping the enemy offensive, and by the morning of the 18th the Americans dominated the positions around the Marne. The first day of the counter-offensive had magnificent results. The Germans were forced back on a 28-mile front, for a depth varying from 3 to 6 miles, and the Americans captured 4,000 prisoners and 50 guns. Twenty French towns were delivered, and the Germans began what appeared to be a precipitate retreat. Foch's attack was mainly on the flank of the crown prince's army, which had been left exposed in the rush toward Epernay and Châlons, far south of the Marne. The infantry attack was made with little or no artillery preparation. The German general, Von Boehm, was plainly caught napping.