Free This type is now little used save as a means of communication from a be leaguered city or fortress. There being no means of steering such craft they are as likely to be wafted toward the enemy as toward their friends, as in the case of those liberated during the siege of Paris in 1870, many of which fell into the hands of the Prussians.
Military The military dirigible is used extensively for night scouting, bombing, and to some extent for transportation of mili tary personnel. Hundreds of dirigible balloons, ranging in size from the small about 180 feet long, to the huge Zeppelins, 700 feet long, were used in the late European War. The °Blimps)) were used mostly for coast patrol and for convoying ships; the large dirigibles were used primarily for bombing. Three types of dirigibles are used: (1) the rigid; (2) the semi-rigid, and (3) the non-rigid. The rigid type of dirigible is one in which the shape of the as compartments is maintained by means of rigid framework. The semi-rigid dirigible has a rigid longitudinal frame usually below the gas bag; this frame serves to distribute evenly the ascensional strains against the supported weights of engines, crew, etc., to prevent buck ling of the gas bag which in most dirigibles of this class depends upon internal gas pressure to maintain the shape of the envelope. The non rigid dirigibles depend entirely on gas pressure within the envelope to maintain shape, the nacelle, or body, being suspended by a net of longitudinal canvas bands sewed to the enve lope. The chief advantage of the non-rigid is that it can be transported deflated; its defect that a rent in the gas bag puts it out of commission. In France dirigibles are classed according to volume, which runs from 2,000 cubic metres for the Vedette class to over 10,000 cubic metres for the cruiser or dread nought type. The latter is especially favored because of its greater range, speed and lifting power. These ships are equipped with rapid fire guns to repel attacks by hostile aircraft, with wireless equipment in order to communi cate with its base. It is however as a bomb ing machine that these heavy machines find their best field. For reconnaissance purposes the aeroplane is superior. The bombing raids on London throughout the war show the possi bilities of attack of the large dirigible type. With the development of anti-aircraft guns, dirigibles were obliged to keep at a greater height when dropping bombs and thus their accuracy of aim was greatly impaired. The verdict of most experts having in view the per formances of dirigibles during the late war is that they have been a disappointment. They cannot be safely employed in daylight hours because of their vulnerability to hostile aero planes; their great cost as compared with aero planes—about 50 to 1— is disproportionate when it is remembered that the aeroplanes can, with a greater margin of safety, perform simi lar functions. The problem for sheltering diri gibles is also a serious one.
Aeroplanes.— The Wright, Farman and Bleriot machines (see AERONAUTICS) may be considered as the parent types from which has been evolved the large variety which at the present time are at the disposal of the military aviator. Among the various types which have sprung from the parent forms we search in vain for any underlying new principles. There is, however, in the various types plenty of variety of constructional detail. Perhaps the two most important features of modern military aero plane work are (1) the gradual substitution of steel in place of wood, and the general strength ening of aeroplane construction; (2) the ar moring of vital parts of aeroplanes for the ex igencies of warfare. Regarding the various types of machines now available, it must suffice here to especially mention the features of spe cial interest for the purpose of warlike oper ations. As the military operations in Europe developed it became apparent that the aeroplane was suitable for very many military purposes. It is from the air that artillery fire is regulated, after the airmen have reconnoitred and photo graphed the enemy's position, taken the plan of their trenches and discovered the importance and emplacements of their batteries. It is from
the air that the arrival of reinforcements by rail or motor is signaled. By means of aerial bombardments attempts are made to cut, or at least disorganize, the enemy's communications. These attempts are made even on the base rail way stations, and, further still, on the facto ries and powder and ammunition dumps. Dur ing the battle the aeroplane flies over the troops and regulates the lengthening of the fire as the assaulting force advances. Four years of war resulted in the subdividing of types and their relegation to various specific duties. Scouting is the first and widest use of the aeroplane in war. For this work fast monoplanes and bi planes have been developed into the strategical reconnaissance type, with a cruising radius of 500 miles, carrying pilot and observer with sketching outfit, aerial camera, wireless set and navigating instruments. The tactical-reconnais sance aeroplane has similar personnel, only the observer is trained in military tactics and trans mits technical reports of enemy movements. The fire-control aeroplane is designed to give a particularly wide range of vision to the ob server, who transmits the results of his observa tions by wireless. There are two classes of long-range bombers, the machine of excessive speed with pilot and bomber, and the multiple engined machine, with heavy bomb load, great wing spread, pilot and two bomber-mechanics. The pursuit machine takes many forms — mono plane, biplane, triplane — one-place and two place, highly powered and with minimum aero foil to permit of the maximum of speed and manoeuvrability. The one-place machines are equipped usually with automatic machine guns, firing above or through the propeller zone by means of a synchronizing device. The two place machines are equipped with from two to five machine guns, several automatically fired by mechanisms thrown into mesh by the oper ator and others manually by the operator. In the course of the European War aerial strategy developed from the single machine reconnais sance of 1914 to the flying squadron formation, scouting, fighting and bombing groups, under wireless control from the ground, which were operating in 1918. See AERONAUTICS; AERO PLANE; AEROPLANE ENGINES; SIGNAL CORPS; STRATEGY ; TACTICS; WAR, EUROPEAN.
Bibliography.— Abbott, Willis John, 'Air craft and Submarines; the Story of the Invention, Development, and Present-day Uses of Warns Newest Weapons' (New York 1918); Ader, Clement, 'Avionnerie Mili taire' (Paris 1918) ; Berry, W. H., 'Air craft in War and Commerce' (New York 1918) ; Loening, Grover C., 'Military Aero planes) (Boston 1918) ; Woodhouse, Henry, of Military Aeronautics' (New York 1918) ; Collins, Francis A., 'The Air Man: His Conquests in Peace and War' (ib. 1917) ; Fales, Elisha N., 'Learning to Fly in the United States Army: 'A Manual of Avia tion Practice' (ib. 1917) ; Gill, Napier J., 'The Flyer's Guide: An Elementary Handbook for Aviators' (London 1917) ; Midler, Hollis R., 'Manual of Military Aviation) (Menasha, Wis., 1917) ; Munday, Albert H., 'The Eyes of the Army and Navy' (New York 1917) ; Rolt Wheeler, Francis W., 'The Wonder of War in the Air' (Boston 1917); Widmer, Emil Joseph, 'Military Observation Balloons (Captive and Free) : 1k Complete Treatise on their Manufac ture; Equipment, Inspection and Handling, with Special Instructions for the Training of a Field Balloon Company) (New York 1917) ; Wins low, Carl Dana, 'With the French Flying (ib. 1917) : Woodhouse, Henry, 'Text book of Naval A 1917) ; Ader, Clement, 'L'Aviati,11 militairi ' (10th ed. rev. et corr., Paris 1916) ; I3ek, 'Aerial Rus sia) (New York 1916) ; Crouvezier, Gustave, 'L'aviation pendant la guerre) (Paris 1916); Hearne, It P., 'Zeppelins and Super-Zeppelins) (New York 1916) ; Lafon, Charles, 'Les armies aeriennes modernes' (Paris 1916) ; Lanches ter, Frederick W., 'Aircraft in Warfare' (Lon don 1916) ; Robson, William A., 'Aircraft in War and Peace' (London 1916 ; United States Staff Corps — War College Pi 'ision, 'Military Aviation) (Washintgon 1910). Consult also the Aeronautical Journal (London, quarterly, 1911 et seq.) ; and Aviation and Aeronautical Engineering (New York 1916 et seq.).