On the 15th the Germans counter-attacked. Maunoury was driven out of Nouvron and Autrèches, the British were forced back from Vregny almost to the river, and the Moroccan troops withdrew on Haig's right flank. There was a lull on the 16th, and on the 17th Maunoury recovered the quarries of Autrèches; but east of Reims the 9th Army had fallen back from the Suippe, and the Prussian Guard had captured Nogent l'Abbesse and was threatening Foch's connexion with Langle in Champagne. The 18th saw little progress on either side, except along the Oise, where Maunoury had as early as the 15th begun to outflank the German right. This success, coupled with the stalemate along the rest of the front, suggested to Joffre a change of strategy. Numerically the opposing forces were not unequal, but the Germans had all the advantages of position. To attack up carefully protected slopes with a river in the rear and its crossings commanded by the enemy's fire, promised little hope of success, and threatened disaster in case of failure and retreat. Accordingly, Joffre, taking some risks by weakening his centre, began on the 16th to lengthen and strengthen his left by forming two new armies. Castlenau gave up his command of the 2nd to Dubail in Lorraine and took over the new 7th, and a 10th was entrusted to Maud'huy, another of the professors of military history to whom the French and the Russian armies owed so much of their generalship. By the 20th Maunoury had swung his left round until it stretched at a right angle from Compiègne north to the west of Lassigny. Castelnau's 7th continued the line north through Roye to the Albert plateau; and on the 30th Maud'huy's 10th took up the tale through Arras to Lens.