The weather during the early part of the Marne battle had been excellent for flying. The air had been still and the heat tropical. On the 9th of September, the critical day of the battle, the weather broke, and for the next few days there were violent storms and heavy rains which greatly impeded air work of any sort. The worst of these storms occurred on the night of the 12th of September, when the squadrons had newly arrived at Saponay. Four machines of No. 5 Squadron were completely wrecked, and others damaged. Lieutenant L. A. Strange saved his Henri Farman machine, which had made a forced landing, by pushing it up against a haystack, laying a ladder over the front skids, and piling large paving-stones on the ladder, using hay twisted into ropes for tying down the machine. A diary of No. 3 Squadron records that when the machines of that squadron arrived at Saponay, about five hours before the transport, 'a terrible storm was raging, and before anything could be done to make the machines more secure the wind shifted, and about half the total number of machines were over on their backs. One Henri Farman went up about thirty feet in the air and crashed on top of another Henri Farman in a hopeless tangle. B.E.'s of No. 2 Squadron were blowing across the aerodrome, and when daylight arrived and the storm abated, the aerodrome presented a pitiful sight. The Royal Flying Corps in the field had probably not more than ten machines serviceable that morning.... Hangars were not yet issued.' The protection of machines from accidents like this became comparatively easy when the line of battle was stabilized and fixed aerodromes were made. On Sunday, the 13th of September, the Allied armies had crossed the Aisne, but were held up by the enemy line of defence which, ran along the heights from east of Compiegne to north of Rheims. There was dogged fighting, with attacks and counter-attacks, but little or no progress was made. The Germans had regained the initiative, and the British army was forced to dig itself in along the line of battle. On the 18th of September General Joffre changed his plans and began to push forces up on the Allied left in order to envelop the German right flank. To give this movement a chance the enemy had to be held on the front, and the cavalry were called on to take their turn in the trenches--a duty which before long became very familiar to them. But the Germans extended and reinforced their line for a similar outflanking movement. These enveloping attempts did not cease until the opposing armies were ranged along a line of trenches stretching from the Swiss frontier to the coast of Belgium.