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 Ferté 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 Château-Thierry, and the Second Army between the Marne and the Seine, occupying the Seine crossings from Nogent to Méry. 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.
Their work during the retreat was done under difficulties. There were alarms at Compiègne of Uhlans seen in the vicinity of the aerodrome, and a guard was provided from the Camerons. Major B. H. Barrington-Kennett remarks on the difficulty of defending a Flying Corps camp from attack by cavalry. It would seem advisable, he says, when camped in an open aerodrome to park the aeroplanes inside a laager formed by lorries and cars. The head-lights of the cars would lighten a good field of fire, and would probably, if switched on at the approach of cavalry, cause the horses to stampede. The Royal Flying Corps, he adds, should be armed and practised with machine-guns and rifles, so that they may protect themselves without asking for an escort.
At Juilly on the 1st of September there was another alarm. The country to the north was thickly wooded, and German cavalry, which proved later to be those escaped from the affair at Néry, were reported within a few miles, with no British troops between. General Headquarters at Dammartin-en-Goële, some two miles away, hastily took their departure, and the Royal Flying Corps transport was sent off at once to Serris. But the aeroplanes could not leave, for already it was dark. The suggestion was made that the aeroplanes should fly off in the dark, but fortunately, says Major C. J. Burke, this was not attempted. The Flying Corps stood to arms to defend itself. A sunken road running east and west past the aerodrome was occupied, rifles and ammunition were served out to the mechanics, and machine-guns were set in position. After a time a troop of North Irish Horse arrived, to aid in the defence. All night watch was kept, but the German cavalry did not appear. In the morning, for the first time since the beginning of the retreat, there was no ground mist, and the machines got away at once.
The history of the retreat is made up of incidents like this. Some of the flying officers have kindly communicated their memories and impressions. 'The extraordinary part about the retreat', says Wing Commander P. B. Joubert de la Ferté, 'was the contrasts that one experienced from day to day; one night sleeping under a hedge in a thunder-storm; the next in a comfortable private house; the third in the most modern type of hotel with every luxury and convenience, the whole forming a picture the impression of which has lasted throughout the war.... One curious thing was, unless one was brought down or left behind near the firing line one never came up against the actual unpleasantnesses of war, and it was not until the advance to the Aisne started that those of us who had not been on ground duty, or unlucky, saw any signs of fighting other than from the air. What we saw during the advance confirmed our impressions from the air as to the unspeakableness of the Hun in his methods of dealing with the civilian population. I saw half a dozen villages on fire during the first day of the battle, twenty miles west of Mons, where by no possible means could there have been any armed resistance to the passage of the Huns. It was simply frightfulness on the part of the Uhlans, and what we saw later on the ground at Pezarches, Coulommiers, and La Fère was a clear indication of wilful and unnecessary destruction of private property. The sight of a draper's shop with every window smashed, every shelf emptied, and the contents thrown into the street was quite a common one.'
Major F. G. Small says, speaking of the 27th of August: 'The retreat continued to Compiègne Forest, Huns pressing our troops all the while. On returning from late reconnaissances in the dusk, it was most interesting to watch the local fighting in the roads between their vanguards and our rearguards. The spreading of fires all over the country around Compiègne Forest was a more curious sight than even the later trench offensive, the fires spreading like long flaming worms along the main road, as the Huns fired each village they went through. The northern portion of Compiègne Forest was blazing at this date.'
The speed of the retreat caused some embarrassments. On the 31st of August, while the Flying Corps occupied Senlis racecourse, two officers, belonging to Nos. 4 and 5 Squadrons, motored to Paris to get some aircraft spares, and returning in the evening found the Germans in occupation. In the dusk they were mistaken for German officers and drove their car right up to the cottages which a few hours earlier had been the headquarters of the Flying Corps. Aviation teaches quick resource; the officers managed to escape.
The pilots were not down-hearted. At Compiègne, where they were billeted in a school, Major Baring records that they were in tearing spirits. Besides their main duty of observation from the air, they rendered other occasional services. 'The usual orders on the retreat', says Wing Commander L. A. Strange, 'were dawn reconnaissances, dropping hand-grenades and petrol bombs on the enemy, and when it was impossible to notify pilots of the next aerodrome, the orders were to fly approximately twenty miles south and look out for the remainder of the machines on the ground, if machines had left the last aerodromes.'
During the retreat the dropping of bombs was still in an early experimental stage. There were some mildly successful exploits. About dusk on the 1st of September an unnamed officer of the Flying Corps, flying over the woods north of Villers-Cotterets, noticed two columns of the enemy's cavalry converging at the angle of cross-roads. He dropped two bombs, which caused confusion and a stampede. There was no bomb-dropping gear in use at this time, but small hand-grenades were carried in the pockets, and larger bombs were slung or tied about the person. The first experience of German bombs was at Compiègne on the 29th of August; while the Flying Corps were stationed there a German machine flew over the aerodrome and dropped three small bombs, which did no harm. On our side there was no time during the retreat for experiment with new devices; it was not until the Germans took up fixed positions on the Aisne that the inventive powers of the Flying Corps got to work on the devising of bombing gear, the improving of artillery observation, and the mounting of machine-guns.
The retreat also witnessed the beginnings of fighting in the air. The first German machine to be seen by the British appeared over the aerodrome at Maubeuge on the 22nd of August. There are various accounts of this. Major C. J. Burke in his diary says: 'At about 2.25 p.m. an Albatross biplane passed over the town. Major Longcroft with Captain Dawes as passenger, Lieutenant Dawes with Major Burke as passenger, on B.E.'s, gave chase. The gun machine piloted by Lieutenant Strange also went out. The machine (Albatross) had far too long a start, and got into a rain cloud.' Wing Commander L. A. Strange says: 'Chased a German Albatross machine for forty-five minutes, Lieutenant Penn-Gaskell observer, with Lewis gun. Was unable to get higher than 3,500 feet, while the Albatross was at about 5,000 feet. Observed no effect from the fire. As a result of this received orders to discard Lewis gun and mounting, and transfer the controls from rear seat to the front seat, the passenger to carry rifle in the back seat.' Major J. T. B. McCudden says: 'About the 22nd August a strange aeroplane flew over us at about 4,000 feet, and the aerodrome look-out reported it to be a German machine, the first we had seen in the War. We all turned out armed with rifles, and about six machines got ready to go up in pursuit.... All the machines which went up were loaded with hand-grenades, as the intention then was to bring a hostile aeroplane down by dropping bombs on it. The German easily got away, although it looked at one time as if Captain Longcroft would be able to intercept him on a B.E. 2 a. About half an hour after the German had departed a Henri Farman of No. 5 Squadron, fitted with a machine-gun, was still climbing steadily over the aerodrome at about 1,000 feet in a strenuous endeavour to catch the Boche.'