The beginning of the alteration of German plans was noticeable at Creil. Hidden by a thick screen of troops from the army in the field, but observed by aerial squadrons, the enemy were seen to be on the move. Ground won at Senlis was given up, and the German troops, which at that point were nearer Paris than any other men of the Kaiser's army, were marched to the rear. Only the commandants in the field can say whether the movement was expected, but it is the fact that immediately the enemy began their strategic movement British and French dispositions were changed. The movement _was_ expected. Indeed, as we have seen, the whole strategy of the campaign on the French side had been designed to bring it about. The Germans must have observed that their new intentions had been noticed, but they steadily pursued their policy. Their right was withdrawn from before Beauvais, and that pretty cathedral town has now been relieved of the danger of Teuton invasion. The shuttered houses are safe, temporarily at any rate. The ponderous machine did not turn at right angles with any rapidity. Its movements were slow, but they were not uncertain, and the change was made just where it was anticipated the driving wedge would meet with least resistance. In the main the German right is a tired army. It is a great fighting force still. The advance has been rapid, and some big tasks have been accomplished. But the men have learnt many things which have surprised them. They thought they were invincible, that they could sweep away opposition like a tidal wave. Instead of a progress as easy as modern warfare would allow, their way has had to be fought step by step at a staggering sacrifice, and in place of an army which took the field full of confidence in the speedy ending of the war and taught that nothing could prevent a triumph for German arms, you have an army thoroughly disillusioned. In this connection the service of the British Flying Corps proved invaluable. Covering though they did a vast area, and carefully as they were screened by ordinary military precautions, the movements of the Germans were watched and notified in detail. Upon this, as far as the dispositions of the Allied forces were concerned, everything depended, and no one knew that better than General Joffre. On September 9 he acknowledged it in a message to the British headquarters:-- Please express most particularly to Marshal French my thanks for services rendered on every day by the English Flying Corps. The precision, exactitude, and regularity of the news brought in by its members are evidence of their perfect organisation, and also of the perfect training of pilots and observers.