Next in order of importance is wind. The engine may be giving a speed of sixty miles per hour, and the craft be flying in the teeth of a 20 m.p.h. wind, thus its actual speed would be forty, not sixty, miles an hour. Again, two enemy machines, A and B, are approaching one another to give battle. Both have a speed of 60 m.p.h., but A is flying “down” with a fifteen-mile wind at the back of him. Their relative speeds would be: A seventy-five, B forty-five, or an advantage of thirty miles an hour for A; but on the turn--the majority of aerial combats are fought out on the principal of circling and wheeling--the advantage would be transferred to B. Good pilotage is of extreme importance; the pilot who is able to get the most out of his machine and knows it best will almost invariably gain the day. Clouds are often made great use of by pilots. Almost every day we read of a machine dashing out from behind a bank of cloud, and taking another by surprise. On the other hand, clouds may prove disastrous to both combatants, owing to the peculiar property they possess of influencing the stability of the machine. Lift, however, is still the great factor, since the fight always develops into a struggle for the upper berth, and is usually fought in an upward direction. It is climb, climb, climb; then, with the wind at his back, a last swoop down on the enemy--taking him in his most vulnerable position--and the fight is over. Various expedients are made use of to gain this end, such as getting between an opponent and the sun, “diving” suddenly and “looping.” With either aeroplane or airship it is the uppermost position that counts. The type of craft most useful for this work is the high-engined biplane of the “tractor”--propeller to the fore--type, the machine-gun firing through the blades of the propeller. The essentials of these machines are speed and ability to climb quickly. The slower machines, with greater powers of endurance, are more useful for bomb-raiding and reconnaissance purposes. “LIFT” THE FACTOR Airship combat has yet to materialize. Many opinions and theories, often widely conflicting, have been put forward concerning the possibilities and probabilities of such conflicts, but nothing definite can be advanced until a battle between airships has taken place. The opinion of the majority of the experts is that an airship would be little better than useless to meet an airship, and for our own particular requirements--that is, the repelling of Zeppelin raids--aeroplanes are of more use; which brings us to the combat between aeroplane and airship. Considering first their main qualities: the airship has great “lifting” powers, is more heavily armed, can climb at a faster rate, and has greater powers of endurance; whereas the aeroplane has greater speed, is more easily maneuvered, and is less unwieldy.