The Reserve group was to operate with the X. and VI. Armies. The X. Army, under Gen. Mangin, who was responsible for the principal attack, had io divisions in front line, including the American 1st and 2nd Divisions, placed on the flanks of the Moroccan Division in the centre of the army, and six divisions in second line, making a total of 16 infantry divisions—besides three cavalry divisions. In the rear of the army the British 15th and 34th Divisions were in reserve. In addition, the army was given a large number of tanks and strong artillery reinforcements. The task which Mangin set before his troops was "to break through the enemy front between the Aisne and the Ourcq and push straight on in the direction of Fere-en-Tardenois in liaison with the offensive of the VI. Army." On his right the VI. Army, com manded by Degoutte, whose own right was engaged in the de fensive battle, had only seven divisions in front line—among them the American 4th and 26th Divisions (American I. Corps)—and one division in second line. Degoutte was to attack with his own resources only, reinforced, however, by tanks and by British bombing aircraft.
The attack had been prepared with infinite precautions for maintaining secrecy. The reinforcing divisions were only brought up to the front during the last two days, their movement being carried out by night, between July 14 and 16, the mounted ele ments marching and the unmounted carried by motor transport. A violent storm which burst during the night of the i7th-18th intensified the darkness and made movements in the woods diffi cult; but it was favourable to surprise and by 4 A.M. the attack ing divisions of the X. and VI. Armies were in position and ready to move without any sign of uneasiness having been shown by the enemy. At 4.35, without a single preliminary round, the whole of the artillery opened fire from the Aisne to the Marne, and 16 front line divisions moved forward with the tanks, while all the air squadrons went up. In the X. Army the infantry and tanks advanced without an artillery preparation behind a rolling bar rage, turning the enemy's strong defensive positions and quickly gaining a footing on the plateau north-east of the forest of Villers Cotterets. In the VI. Army, on the contrary, the attacking di visions continued their artillery preparation against the enemy's defensive position for i hours, and only attacked at 6:15 A.M.
on that of the II. Corps, which came under oblique fire from the heights of Chouy. Mangin received information of the first results achieved towards 8 o'clock, and exploited them without delay by the judicious use of his reserves. Robillot's Cavalry Corps, however, had experienced extreme difficulty in debouching from the forest of Villers-Cotterets, as it was encumbered with troops and baggage, and could as yet operate only with dis mounted squadrons. On the first day the enemy lost 12,000 prisoners and 25o guns. The battle raged throughout the night and the next day. The two French armies made substantial progress, even in the difficult region of Louatre-Chouy-Neuilly Saint-Front, where the XI. and II. Corps combined their attacks to subdue the enemy resistance. The bombing aircraft attacked the Marne crossings and the enemy concentrations at Oulchy-le Château and Fere-en-Tardenois.
Meanwhile the centre group was preparing to clear the south bank of the Marne. But its units were exhausted by resisting the German attacks of July 15-18, and to reinvigorate them the British XXII. Corps (51st and 62nd Divs.) was brought in to relieve the Italian Corps. 'Detain took care to insist that it was not a question of a simple relief. "It will be carried out on the move—that is to say, it will take the form of a surprise attack, carried out with the co-operation of the French units on either side." Nevertheless it was not until the loth that the Centre group was able to push forward. On that day its IX. Army reached the south bank of the Marne, evacuated by the enemy during the night, while in the V. Army the British XXII. Corps was heavily engaged in the Courton wood.
The fighting continued to be severe throughout July 21 and 22. On the two extreme wings the Germans offered a stubborn re sistance to the attacks of the X. and V. Armies which pressed on their flanks. It was clear that they were seeking to gain time to evacuate the material and troops that had been pushed into the Marne "sack." On July 21 the French 3oth Division reoccupied Château-Thierry, and the American 3rd Division crossed the Marne to the east of the town, and entered the Barbillon wood. In the VI. Army the American I. Corps and the French VII. and II. Corps advanced on the plateau of Etrepilly and Latilly, and on the 22nd, at noon, the VI. Army re-established its communica tions by way of Chateau-Thierry. On the same evening fractions of the V. and IX. Armies gained a footing north of the Marne.