No. 5 Squadron from the first had been zealous in experimenting with machine-guns. Experience of fighting in the air, which began with this adventure, soon taught how enormous is the advantage, whether for attack or escape, given by superiority in height.
It was not, however, until the 25th of August that an enemy machine was brought down by a British aeroplane. Sir John French in his first dispatch, dated the 7th of September 1914, alludes to the earliest combats. His tribute must be quoted in full: 'I wish particularly to bring to your Lordships' notice the admirable work done by the Royal Flying Corps under Sir David Henderson. Their skill, energy, and perseverance have been beyond all praise. They have furnished me with the most complete and accurate information, which has been of incalculable value in the conduct of operations. Fired at constantly both by friend and foe, and not hesitating to fly in every kind of weather, they have remained undaunted throughout. Further, by actually fighting in the air, they have succeeded in destroying five of the enemy's machines.'
Unfortunately during the retreat combat reports were not made out, so that there is no account in the war diaries of the actual fighting. Some of the fights are mentioned. On the 25th of August three machines of No. 2 Squadron chased an enemy monoplane. It was forced to land; Lieutenant H. D. Harvey-Kelly and Lieutenant W. H. C. Mansfield landed near it and continued the chase on foot, but the Germans escaped into a wood. When some trophies had been taken from the machine it was burnt. Another German machine was forced to descend on the same day near Le Quesnoy, where it was captured. Aeroplanes at this time had no special armament; officers carried revolvers and sometimes a carbine; but the confidence and determination with which they attacked did the work of a machine-gun, and brought the enemy down. In one instance, a little later on, a British pilot and observer, who were destitute of ammunition, succeeded by manœuvring boldly above a German machine in bringing it to the ground and taking it captive.
On the afternoon of the 5th of September neither the German Supreme Command (which had its headquarters at Luxembourg) nor the staff of the German First Army had any idea that an offensive of the whole French army was imminent. The Supreme Command was expecting a decisive victory in the east against the Verdun-Nancy-St.-Dié defences. They believed that the German First and Second Armies could easily hold the weak French forces around Paris until this decision should be achieved, and they did not know how great a part of the French strength had been transferred from the east to the west. From the 5th to the 9th of September they issued no orders to their First and Second Armies, who were left to fight out the decisive battle of the war, without their help and almost without their knowledge, against superior forces.
General Joffre's 'Instruction' for the offensive on the 6th was brought to British General Headquarters by a French staff officer at 3 a.m. on the morning of the 5th. Unfortunately, orders to the British army to continue the retreat in accordance with General Joffre's previous instructions had already been given to the corps commanders. The Second Corps had moved off before midnight and the First and Third Corps a little later. Consequently the British army by the end of the day was some twelve to fifteen miles farther back than the French Commander-in-Chief expected, and although its subsequent advance across the Marne had a decisive effect, the hard fighting of the battle was borne by the French army on the Ourcq. During the 5th, General Maunoury, commanding the Sixth French Army on the British left, and later on General Joffre himself, visited Sir John French, and all arrangements for the morrow's offensive were discussed. Sir John French's operation orders issued at 5.15 p.m. on the 5th of September directed the army to advance eastward with a view to attacking. The preliminary movement of the British army, a wheel to the east, pivoting on its right, was to be completed by the right wing at 9 a.m. and by the left wing at 10 a.m. on the 6th.
On the early morning of the 6th Sir John French gave verbal instructions that the Royal Flying Corps were to send aeroplanes to report for reconnaissance direct to the First and Second Corps. The officer commanding No. 5 Squadron, with three machines, was to report for tactical reconnaissance direct to Sir Douglas Haig at Chaubuisson farm, one and a half miles east of Fontenay; and the officer commanding No. 3 Squadron, also with three machines, was to report direct to Sir Horace Smith-Dorrien at Combreux Château, near Tournan. With each detachment was to go a wireless aeroplane from No. 4 Squadron to keep Royal Flying Corps headquarters informed by wireless. The machines were to return to headquarters at night. This was the beginning of the decentralization of the Royal Flying Corps, whereby certain squadrons, which came to be called corps squadrons, were attached to the corps commands. The German air service from the beginning had been thus organized. With the German First Army headquarters there was one aeroplane section for long-distance strategic reconnaissance and each of the corps, with the exception of the Fourth Reserve Corps, had its own section for tactical work. From Maubeuge to the Marne the squadrons of the Royal Flying Corps had been kept together under the immediate control of General Henderson. The experiment of detaching machines to report direct to the First and Second Corps worked well on the 6th of September, and Sir John French gave orders that this arrangement was to continue.
Aeroplanes which were sent out on the morning of the 6th brought information of confused movements of the German First Army. On the British front a certain amount of movement northwards was seen in the afternoon. Of the progress of the battle on his flanks Sir John French had little knowledge. Aeroplanes were sent up to reconnoitre the position. One which flew over the area of the Sixth French Army west of the Ourcq saw at about five o'clock a good deal of movement and shells bursting in the area Étavigny-Marcilly-May-en-Multien. Another machine which flew along the line of the Fifth French Army on the British right came back with the information that at four o'clock fighting was going on south of Esternay and north of Villiers-St.-Georges. By seven o'clock that evening Sir John French had no definite news of the progress of the French armies on his wings save what was contained in these air reports, and the orders which he issued stated simply that all troops should be ready to move at any time after 8.0 a.m. on the morrow.
Early on the 7th the situation became clearer; a general retirement of the Germans on the British front was in progress. Sir John French had issued orders at 8.0 a.m. for the advance to be continued in the direction of Rebais, the army to move in echelon from the right and to attack the enemy wherever met. Aeroplanes on morning reconnaissance returned soon after the army began to move with information of early activity behind the German lines and general movement northwards. Later in the morning columns were seen moving in a north-westerly direction towards the Ourcq. These reconnaissances seemed to show that von Kluck was hurriedly withdrawing two of his corps—the Second and the Fourth—to reinforce his right wing across the Ourcq.
Early reconnaissances on the 8th told of congested movement over the bridge at La Ferté-sous-Jouarre, south of which masses of troops were awaiting their turn to cross. But the British advance was necessarily slow. The country was well suited to rearguard actions and skilful use was made of the ground by the German machine-gunners. By the evening the British had forced the passage of the Petit Morin, but they spent the night south of the Marne. Meantime, as air reports showed, von Kluck's right was heavily engaged by Maunoury's Sixth Army to the west of the Ourcq. On the night of the 8th General Joffre, taking advantage of the withdrawal of the two German corps from the British front, ordered that Maunoury's army should hold the enemy troops on the right bank of the Ourcq, whilst the British on the following day should advance across the Marne between Nogent l'Artaud and La Ferté-sous-Jouarre against the left and rear of the enemy on the Ourcq. The Marne with its steep wooded sides was well suited to rearguard actions and a stubborn resistance was expected. But air observers who came in early on the morning of the 9th brought back the news of enemy columns formed up facing in a northerly direction. Some were already on the move, and it became apparent that the enemy intended no determined, but only a delaying stand on the Marne.
Captain D. Le G. Pitcher, piloted by Lieutenant G. W. Mapplebeck, whilst reconnoitring near Château-Thierry about 12.45 p.m. saw large bodies of enemy troops in the neighbourhood of Château-Thierry and infantry moving on Domptin. This position was west of the British Third Infantry Brigade, and the whole of the First Corps was ordered to halt until the situation should be cleared up. The First Corps did not move forward again until 3.0 p.m. By the evening of the 9th the First and Second Corps were across the Marne, but the Third Corps on the left had been held up and was mostly south of the river. General Maunoury had had a hard fight, but by the late afternoon the Germans, pressed by the advance of the British across the Marne, had begun to retire in a north-easterly direction. Captain R. A. Boger, piloted by Captain R. Grey, brought this welcome news direct to the General Officer Commanding the Third Corps (Lieutenant-General W. P. Pulteney) at 5.0 p.m. He had seen long columns moving north-east from Lizy through Ocquerre on to Coulombs. This was believed to be von Kluck's Fifth Division. Other observers came in with similar information. By the evening of the 9th the retirement of the enemy was general from the Ourcq to Verdun. The battle of the Marne was won. The German armies retired, with no very great disorder, to strong positions along the heights of the northern bank of the river Aisne. Paris was saved; for the first time for over a hundred years an invading Prussian army had been turned and driven back; but the war was yet to come.