For nearly four years this war of tools and this war in the air went on with fluctuating vicissitudes for Hun and Ally. First came the German scouting and fighting Fokkers equipped with motors which owing to their superior horse-power made them faster and more easy to manœuvre than anything the Allies had until the famous French Baby Nieuports with 110 horse-power Le Rhone engines appeared in 1916 and began to equal the Boche in those two prime requisites. Then, owing to the number of machines shot down or forced to land through engine trouble, neither side could long keep any secret of aeromotor construction or aeroplane design from an opponent. Therefore the struggle for quantity production began. In the meantime the huge bimotored Caudrons, Voisins, Breguets, Handley Pages, and Capronis began to be built in large numbers by the French, British, and Italians, and the Gothas by the Germans. Each year saw an increase in the horse-power of the motors and in the size of the aeroplanes; and still, owing to the infinite area of the skies to manœuvre in and the lack of large aerial fleets flying as a unit, neither side could prevent the scouting-machines or the bombing raiders from spying out or bombing any objective within a flying radius of two hundred miles of their aerodromes. With the advent of the United States into the struggle it became more and more apparent to the German military leaders that they must win the war before the tremendous manufacturing and aviator resources of this country could be felt on the West Front. That, of course, was one of the cardinal reasons for the series of great German drives beginning with March 21, 1918. The Allies, too, now fully realized that the Great War would be won in the air, so they expended every effort and resource to build aeroplanes to clear the German machines from the skies and to bomb Germany from the air. How much these raids behind the Boche lines had to do with the breaking down of the morale of the German people and Teuton soldier cannot yet be properly estimated. However, to give an idea of the severity of this war in the air and destruction wrought by bombing-machines in Germany we know that the British Independent Air Force sent out over the enemy territory squadrons of five to one hundred aeroplanes, which dumped daily, rain or shine, sixty to one hundred tons of high explosives on military objectives and manufacturing plants scattered over a belt a hundred miles wide all along the Rhine Valley. These raids penetrated as far as Essen and Heidelberg. They destroyed ammunition-dumps, railroad-yards, chemical and gas works. By blowing up railroad communications with the rear they virtually cut the arteries of the German army. Moreover, by their repeated excursions into Holland they disrupted the sleep, the rest, and the working capacity of the people in the manufacturing towns and cities in southern Germany.