Something must be said of the machines which flew to France. Experience at manœuvres had favoured the factory B.E. 2 biplane; of the other types most in use the Henri Farman had been found fatiguing to fly, and the Maurice Farman was too slow. Accordingly, in the winter of 1913-14 Lieutenant-Colonel F. H. Sykes had urged the gradual substitution of B.E. machines for the Farmans. Major W. S. Brancker, writing for the Director-General of Military Aeronautics, objected to this proposal on the ground that until a satisfactory type of fighting aeroplane should be evolved, the Henri Farman was the only machine that could mount weapons effectively; and further, that a slow machine had some advantages for observation. The first of these objections was not fully met until firing through the airscrew was introduced; the second was for a long time an accepted idea. The war was to prove that a slow machine, exposed to armed attack, cannot live in the air. The battle of the machines ended, for the time, in compromise. It was judged important that the Flying Corps should have four squadrons ready for war by the spring of 1914, and large changes would have caused delay. In the event, at the date of mobilization, No. 2 Squadron and No. 4 Squadron were furnished throughout with B.E. 2 machines; No. 3 Squadron made use of Blériots and Henri Farmans, and No. 5 of Henri Farmans, Avros, and B.E. 8's. A single type of machine for a single squadron is a thing to be desired; the squadron is easier for the pilots and the mechanics to handle; but in the early days of the war there was no formation flying; each machine did its work alone, so that uniformity was of less importance.

When the Flying Corps arrived in France they were received by the French with enthusiasm, and had their full share of the hospitality of those days. The officers were treated as honoured guests; the men with the transport were greeted by crowds of villagers, who at all their stopping-places pressed on them bottles of wine, bunches of flowers, fruit, and eggs. At Amiens the transport and machines were parked outside the town, without cover, and the officers were billeted at the 'Hôtel du Rhin' and elsewhere. The hardships of the war were yet to come. Lieutenant B. H. Barrington-Kennett, with his mind always set on the task before them, remarks: 'There seemed to be a general misunderstanding amongst the troops as to the length of time during which rations have to last. They were apt to eat what they wanted at one meal and then throw the remainder away. R.F.C. peace training does not encourage economy with food, as the men are financially well off, and can always buy food and drink in the villages.'

On Sunday, the 16th of August, the headquarters of the Flying Corps, the aeroplanes of Nos. 2, 3, and 4 Squadrons, and the transport of Nos. 3 and 4 Squadrons moved from Amiens to Maubeuge. Second Lieutenant E. W. C. Perry and his mechanic, H. E. Parfitt, of No. 3 Squadron, who were flying a B.E. 8 machine (familiarly known as a 'bloater'), crashed over the aerodrome at Amiens; the machine caught fire, and both were killed. There was another accident on the 18th, when the aeroplanes and transport of No. 5 Squadron followed. Second Lieutenant R. R. Smith-Barry and Corporal F. Geard, also flying a B.E. 8 machine, crashed at Péronne; the officer broke several bones, and the corporal was killed. Three of these machines in all were flown over at the beginning; they had been allotted to the Aircraft Park, and were taken on charge of the squadrons in the field to fill vacancies caused by mishaps. The third of them was the machine flown over by Captain G. I. Carmichael.

At Maubeuge the French authorities gave all the help they could, providing blankets and straw for the troops. The Flying Corps were now in the war zone, but for the first two or three days the conditions were those of peace. They saw nothing of the British army till one evening British troops marched through Maubeuge on their way to Mons. 'We were rather sorry they had come,' says Wing Commander P. B. Joubert de la Ferté, 'because up till that moment we had only been fired on by the French whenever we flew. Now we were fired on by French and English.... To this day I can remember the roar of musketry that greeted two of our machines as they left the aerodrome and crossed the main Maubeuge-Mons road, along which a British column was proceeding.' To guard against incidents like this the Flying Corps, while stationed at Maubeuge, turned to, and by working all night painted a Union Jack in the form of a shield on the under-side of the lower planes of all the machines.

While the Flying Corps remained at Maubeuge and began to carry out reconnaissances over Belgium, the little British army had moved up north to Mons, where it first met the enemy. By the 22nd of August it was in position, on a front of some twenty-five miles, the First Army Corps holding a line from Harmignies to Peissant on the east, the Second Army Corps holding Mons and the canal that runs from Mons to Condé on the west. On the right of the British the Fifth French Army, under General Lanrezac, was coming up to the line of the river Sambre.

The original German plan was broad and simple. The main striking force was to march through Belgium and Luxembourg into France. Its advance was to be a wheel pivoting on Thionville. Count von Schlieffen, who had vacated the appointment of Chief of the General Staff in 1906, had prepared this plan. He maintained that if the advance of a strong right wing, marching on Paris through Belgium, were firmly persisted in, it would draw the bulk of the French forces away from their eastern fortress positions to the neighbourhood of Paris, and that there the decisive battle would be fought. His successor, von Moltke, believed that the French, on the outbreak of war, would at once deliver a strong offensive in Lorraine and so would themselves come into the open, away from the bastion of the eastern fortresses. He must be prepared, he thought, to fight the decisive battle either on his left wing in Lorraine, or on his right wing near Paris, or, in short, at any point that the initial operations of the French should determine. This was not the conception of Count von Schlieffen, who had intended to impose his will on the campaign and to make the enemy conform to his movements. When he was on his death-bed in 1913, his thoughts were fixed on the war. 'It must come to a fight,' were the last words he was heard to mutter, 'only give me a strong right wing.' Von Moltke, though he did not absolutely weaken the right wing, weakened it relatively, by using most of the newly formed divisions of the German army for strengthening the left wing.

The French, when the war came, delivered their offensive in Alsace and Lorraine as had been expected, but not in the strength that had been expected. They were held up, and retired, not without loss, to strong defensive positions covering Épinal and Nancy. Meantime, the advance of the German armies through Belgium was met by a French offensive in the Ardennes, which also failed, whereupon General Joffre ordered a retreat on the whole front, and began to move some of his forces westward, to prepare for the battle in front of Paris.

The successes won by the German left wing and centre against a yielding and retreating enemy were mistaken by the German high command for decisive actions, which they were not. The French armies which had been driven back on the Lorraine front rapidly recovered, and on the 25th of August delivered a brilliant counter-offensive, inflicting heavy losses on the Germans, and in effect upsetting all the German plans. The indecision which marked the movements of the German right wing through northern France had its origin in von Moltke's modifications of von Schlieffen's plans and in the readiness of the Germans to believe that the war was virtually won.[4]

The heroic stand made by the Belgians at Liége purchased invaluable time for the preparations of the Allies. When, on the 17th of August, the last fort of Liége fell, the great wheel of the German northern armies began to revolve. Its pace was to be regulated by the pace of the armies nearest to its circumference; that is to say, the First Army, under von Kluck, and the Second Army, under von Bülow. Three divisions of cavalry were to advance against the line Antwerp-Brussels-Charleroi, moving westward across Belgium in order to discover whether a Belgian army was still in being, whether the British had landed any troops, and whether French forces were moving up into northern Belgium. The Belgian army retired within the defensive lines of Antwerp, and by the 20th of August Brussels was in the hands of the enemy. By the 22nd, von Bülow's army had entered Charleroi and was crossing the Sambre. The repulse of the French centre in the Ardennes left the British army and the French Fifth Army completely isolated on the front Mons-Charleroi. The French Fifth Army began to retreat. On Sunday morning, the 23rd of August, von Kluck's army came into action against the British position at Mons.