Von Kluck had marched into a bag between the Fifth French Army on the Marne and the newly formed Sixth French Army advancing to the Ourcq. Just at this time the German Supreme Command seems to have become aware of the danger threatening the German armies on the right wing. On the night of the 4th of September orders had been sent out from German First Army headquarters at La Ferte Milon, detailing the movements to be made on the following day. These movements had already begun when at 7.15 a.m. on the 5th fresh instructions arrived from the Supreme Command ordering the First and Second Armies to remain facing the eastern front of Paris; the First Army between the Oise and the Marne, occupying the Marne crossings west of Chateau-Thierry, and the Second Army between the Marne and the Seine, occupying the Seine crossings from Nogent to Mery. This led, says von Kluck, to 'the difficult backwards wheel' of the First Army, and to what he calls 'the important events that occurred during the second week of September'--events known to history as the battle of the Marne. Von Kluck allowed the original movements ordered for the 5th to be carried out, and, he says, 'the conclusion of this advance marked the culminating point of the operations of the First Army'. On this same day General Joffre told Sir John French that he intended to take the offensive forthwith as the conditions seemed favourable, and on the morning of the 6th this offensive opened. The main work of the Royal Flying Corps throughout the days of the retreat was reconnaissance, and enough has been said of their reports to show that Sir John French was well served by his new arm. He had been warned before the battle of Mons, not only of the heavy movement on his front but of the enveloping attempt on his flank, and throughout the retreat he was punctually informed of von Kluck's enveloping efforts. The change of direction made on the 31st of August was immediately seen and reported. Von Kluck's renewed pursuit of the British on the two following days did not escape observation. Finally, the German swerve to the left on the 3rd of September was closely followed from the air. These are the main conclusions that come from a study of the air reports of those days. General Headquarters were perhaps at first a little shy of trusting the air reports, but they realized their value during the retreat, and paid more and more attention to them--an attention which found practical results in the operation orders issued. The Royal Flying Corps played their part in helping the British army to escape. Further, they were making themselves, and were improving in skill every day. The lessons learned on the retreat from Mons bore their full fruit at a later period, when the officers of the original squadrons held the command of those Flying Corps units which operated in the mobile campaigns of distant theatres of the war.