As early as 1915 the Germans were using huge battle planes equipped with Mercedes en gines and two machine guns. Many of the French and German aeroplanes were armored on the bottom to permit low flying. On 16 Feb. 1915,.40 French and British aeroplanes and seaplanes bombarded the German lines in Bel gium. In August of that year 32 battle planes. attacked and bombed German munition fac tories at Saarbrfic1cen and later in the same month 62 Allied planes raided De'Hagen.
The year 1916 was notable in military aero nautics for improvements in aeroplane engines by both French and Germans. The Germans iinproved the Mercedes engine and put the Oberussel nine-cylinder air-cooled rotary motor in their Folcker monoplanes. They also used the Benz motors extensively. France devel oped the Hispano-Suiza which weighed only 2.42 pounds per horsepower. England at that time had 500,000 people employed in the air service including many non-combatants and it was re ported that the British expenditures for the year on the air service reached $250,000,000. In America the Wright-Martin Aircraft Cor poration absorbed the Wright Company, Glenn L Martin Company, and others. The Curtiss Aeroplane and Motor Corporation had been greatly developed. When the United States War Department in November 1916 called for bids for 148 service twin-motored hydro-aero planes for coast artillery use, 12 manufacturers submitted proposals, offering both biplane and triplane types. The United States export busi ness in heavier-than-air machines for 1916 amounted to somewhat less than $4,300,000. A much applauded event in American avia tion was a successful flight of 12 aeroplanes from Mineola, Long Island, to Princeton, N. J., on the occasion of the Yale-Princeton football game. In December eight aeroplanes flew from Hempstead Plains, Long Island, to Philadelphia.
In England as decided a novelty was the new °Blimp," a combination of dirigible and aeroplane machines. These miniature airships proved very serviceable for scout and patrol duty over the waters of the British Channel where they easily sailed in circles above the fastest transports and hospital ships en route to or from °Blighty" The Blimps undoubt edly contributed much to the immunity from submarine attack of the ships which ferried armies of men back and forth across the chan nel. Great progress was made by the Gertnans with their Zeppelins and when the British were enabled to inspect one of those giant raiders, the L-33, forced to earth in England, indications were found that this machine had been devel oped to a point which would make possible a non-stop flight 6f at 'least 1,500 miles at 60 miles an hour or better with favoring winds.
In 1916 the Germans made more than 30 air riids on England, destroyed considerable prop erty and killed or injured several hundred peo ple. Thirteen Zeppelins were destroyed.
Formidable fleets of gigantic aeroplanes carrying many tons of high explosives rained. destruction on lines of communication and cen tres of supply far back of the entrenched fronts. Valuable progress was made in the art of photographing the trench areas.
' In 1918 the aerial operations of both sides reflected the intensity of effort characteristic of the climax of the World War.
Both London and Paris suffered severely in air raids, although improved aerial defense systems devised for the protection of both capi tals succeeded in destroying a number of the raiding machines.
British aviators raided and bombed German positions in Belgium and German Lorraine, in cluding Mannheim, Treves, Saarbriidcen and Thionville. They also bombed Mainz, Stutt gart, Cologne, CobLenz, Freiburg, Zweibrucken and Kaisertauten, causing fires and explosions in munition plants and motor-works. In a sec ond raid on Saarbriicken in May five German planes were shot down. British naval airmen frequently raided Bruges, Ostend and Ze.e brugge, dropping tons of explosives. During the war the air raids on England 'caused the death of 1,570 people and the injury of 3,94.1. One hundred and ten raids were carried out by airships and aeroplanes.
In 1917 and 1918 great progress had been made in both construction and skill in handling aeroplanes in war. Speed, manceuvring ability and armament had been so far developed that the smaller scouting and fighting machines attained a velocity of 150 miles per hour. The German Gotha biplane and the British Handley Page biplane carried several men, several guns and from one to two tons of explosives. The Italian Caproni triplane carried three tons of bombs. German battle planes were armed with guns which used four kinds of bullets—ordi nary, perforating, incendiary and explosive.