three thousand feet from the ground a machine would be practically immune from gunfire, and that reconnaissance, to be effective, must be carried on below the level of the clouds. These misconceptions were soon to be corrected by experience. Another, more costly in its consequences, was that a machine-gun, when carried in an aeroplane, must have a large arc, or cone, of fire, so that the gun might be fired in any direction, up, down, or across. To secure this end guns had to be carried in the front of a pusher machine, which is slower and more clumsy than a tractor. But the difficulty of accurate firing from a flying platform at an object moving with unknown speed on an undetermined course was found to be very great. The problem was much simplified by the introduction of devices for firing a fixed machine-gun through the tractor screw, so that the pilot could aim his gun by aiming his aeroplane, or gun-platform, which responds delicately and quickly to his control. When the war began we were not inferior in aerodynamical knowledge to the Germans or even to the French. Speaking at the Aeronautical Society in February 1914, Brigadier-General Henderson said, 'If any one wants to know which country has the fastest aeroplane in the world--it is Great Britain'. This was the S.E. 4, a forerunner of the more famous S.E. 5. If more powerful engines had been installed in the British machines of 1914, they would have given us a speed that the enemy could not touch. But we were preoccupied with the needs of reconnaissance, and we cared little about speed. In the early part of the war we hampered our aeroplanes with fitments, cameras, and instruments, which were attached as protuberances to the streamlined body of the aeroplane and made speed impossible. In the Flying Corps itself an aeroplane thus fitted was commonly called a Christmas tree. We thought too little of power in the engine, a mistake not quickly remedied, seeing that the time which must elapse between the ordering of an engine and its production in quantity is, even under pressure, a period of about twelve months. The engines available at the outbreak of the war for British military aircraft were the seventy horse-power Renault and the eighty horse-power Gnome. In Germany airship engines of two hundred horse-power and more, easily modified for use in aeroplanes, were available in quantity some time before the war. For military machines we were satisfied with smaller engines, which worked well, and enabled our aeroplanes to accomplish all that at that time seemed likely to be asked of them. If we were wrong we were content to wait for experience to correct us.