Before morning the doubled breastwork was defended by a strong wire entanglement. Soon after daybreak the enemy began a terrific bombardment from four guns, two of which had been mounted on platforms behind the two which Lawrence had already seen in position. The garrison could make no effective reply, but could only watch their breastwork crumbling away under the shells that pounded it without intermission. The two brothers held their men some distance in the rear, as much under cover as possible, ready to lead them on and occupy the ruin of the entrenchment as soon as the expected charge began. About ten o’clock they saw Fazl running towards them from the bridge. He had been taking his turn of duty on guard at the aeroplane platform, and the fact that he had left his post seemed ominous. Rushing up to Lawrence, he exclaimed excitedly that he had heard the distant hum of an aeroplane. The boys were incredulous: they themselves were almost deafened by the roar of the guns and the crash of falling masonry. But immediately afterwards, in the interval between the shots, they caught the sound--the continuous throbbing drone, like a gigantic sewing-machine at work. They looked at each other aghast. For a moment or two they were mute: then Bob said: "You must get aloft at once. It’s our only chance. Get above the aeroplane, and bomb it. There’s no time to lose." Lawrence set off at a run, the Gurkha behind him. He raced across the bridge and on to the cantilever pathway, and had just turned the corner when he heard a tremendous explosion behind him. A few seconds later a large monoplane flashed by, and was soon lost to sight up the valley. Long practice had given him facility in starting. The aeroplane was ready for flight. Lawrence and the Gurkha leapt to their places, and within two minutes the machine was in the air, flying after the enemy. This, then, was the meaning of the Kalmuck officer’s veiled warning. The enemy had taken a leaf out of the defenders’ book. Their airmen, equipped no doubt with bombs much more destructive than Lawrence’s home-made missiles, intended to strike at the very heart of the defence, and by rendering the mine premises untenable, clear the way for the advance of the army. Lawrence was fortunately cool of head and a rapid thinker. After a moment of stupefaction he saw his course clearly. The danger from the air must be met in the air. This could only be done by rising above the enemy’s monoplane, and hurling his bombs down upon it. The Kalmuck pilot would be as anxious as he to avoid an actual collision, which must prove disastrous to both the machines. It was wholly a question of manoeuvring for position.