The early development of rigid airships was carried out by Count Zeppelin in Germany, and represents an extraordinary record of perseverance. This development was only rendered possible by political influence and by the repeated financial assistance available. The Schütte-Lanz airships were of wooden construction and developed more slowly. They appear, however, to have embodied considerably more original and perhaps courageous developments than did the Zeppelins, which were developed more as gradual minor improvements on the original design.

British Rigid Airship No. I was started in 1909. During the construction great consideration was given to the various auxiliary gear required by the ship and to the problems included in the handling and mooring as well as the actual flying of the ship. The thoroughness and accuracy with which this auxiliary work was developed is most remarkable in the light of later experience. Before the first flight was made the ship was moored by the bow to a mast with her cars resting on the water. The ship was broken amidships in Sept. 1911 as the result of a mistake in handling while she was being returned to her shed after one of the trials of handling before flight. Comparison of the details and estimated performance of this ship with the contemporary Zeppelins shows that she was a remarkably good first design and that had it not been decided to abandon rigid-airship construction the British development of these ships would almost certainly have become at least equal to that of Germany.

British Rigid Airship R9, by Vickers, stopped at the beginning of the World War, was restarted in July 1915 and made her first flight in Nov. 1916. She made a rather remarkable passage to Howden through a snowstorm over the Pennine range. Being somewhat inadequate in buoyancy, she was used for instruction and ultimately for mooring experiments.

She was followed by four ships of R23 class, built by Vickers, Beardmore and Armstrong, and again by R27 and R29, which were remarkable for the absence of the keel which had existed in all previous rigid airships and had been looked upon as constituting the real strength of the ship to resist bending and shearing forces. This keel subsequently reappeared in German Zeppelins and in the ships built in England, but then merely as a means of distributing to the main frames the weights of petrol tanks, etc., arranged along it.

Two wooden ships, R31 and R32, were built by Short to a design closely similar to that of the Schütte-Lanz type. They were considerably faster than contemporary ships.

Rigid-airship construction in Germany had advanced continuously and was, therefore, greatly ahead of French and British. A combination of the talent and experience of the Zeppelin and Schütte-Lanz firms early in 1916 resulted in the design of L30, giving a speed and performance far ahead of any earlier ships. L33 of this class was brought down in Sept. 1916 in such a comparatively undamaged condition that it was possible from her to prepare a design in England to which R33 and R34 were built. These ships were not, however, completed till late in 1918.

The German L65 class marked a further advance in speed and performance, while the L70 class, of which the first ship, L70, was destroyed on the first flight to England with some of the chief constructional experts on board, marked still further progress in performance and in the simplification of the machinery installation, in the adoption of fins of triangular cross section. L72, which was not actually completed until after the Armistice, again a slightly higher performance.

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After the Armistice Germany built a much smaller airship, the "Bodensee," for commercial purposes, and with her carried out a remarkable series of passenger flights. The ship was then enlarged and a sister ship, "Nordstern," also constructed.

Subsequent to the R33 class the British R36 and R37 were constructed to a generally similar design, of somewhat greater capacity and much improved detail. R80, designed and constructed by Vickers, embodied several entirely new features, but her size was so restricted by the dimensions of the construction shed that her performance was seriously handicapped. R38 made radical changes in features of design, and a clear and definite departure from German methods. The United States had contracted for its purchase. It was to be used, as it was generally understood, for an experimental service from New York to San Francisco and for that purpose masts and intermediate stations were being prepared. R38, while on the final test flight before delivery on August 24 1921, caught fire and fell owing to structural weakness, and many lives were lost.

Non-Rigid Airships. In 1913 the chief general classes of nonrigid airships were: (1) Those with a plain circular envelope from which the car, etc., was suspended from special fittings on

the envelope, and of which the British military airships are typical. (2) The Parseval type, in which the circular envelope is reinforced against bending under the rigging tension by Parseval trajectory bands passing over the envelope and secured to a girdle to which the car is rigged. (3) The Torres type, made by the Astra firm of Paris, trilobe in section, with riggings led inside the envelope and divided into fans secured to points along the two top ridges.

The two latter systems are intended to decrease the distance between the envelope and the car without producing excessive tendency to bend in a large ship.

At the beginning of the war the French had several non-rigid ships of various types which carried out bombing operations, but no important new ships were built. Germany had a few Parseval airships, which did a little work on the Russian front, but there was no important development of small ships. England had three small non-rigids, also one Parseval and one Astra. It became necessary, however, at the beginning of 1915 to develop the very small non-rigid airship as rapidly as possible as an antisubmarine protection. Extreme simplicity was essential in order to allow of rapid production by firms having no previous experience. For the first 30 ships aeroplane bodies were used as cars, but later special cars far more suitable for patrol work were adopted. Engines of about 90 H.P. were used and a crew of three carried. Some 150 ships of the S.S. classes were built, but at the end of the war it had been decided to adopt a slightly larger ship with twin engines and a crew of five as being more suitable for the longer patrols which became necessary. Later in 1915 a larger type the Coastal class-having greater speed and taking a crew of five, was built. For these the Astra system of rigging was adopted in order to reduce to a minimum the necessary height of the sheds. Thirty-five of these ships and ten of an improved (C*) class were built during the war. These ships later carried a crew of five and had an endurance of 12 hours at a full speed of 51 knots. In 1916 the first ship of the North Sea type was flown. This class was intended to work with the fleet and had an endurance of some 24 hours at 50 knots. Sixteen of these ships were built.

The characteristic of these ships, more particularly the N.S. class, was that the petrol tanks and all other weights possible were carried direct on the envelope. In the N.S. class the car was separate from the power unit and the weight distributed over the length of the ship. This gave important advantages over all earlier non-rigids where the loads had been concentrated in the car. The S.S., Coastal and N.S. classes were all designed and built at the R.N. Airship Station, Kingsnorth. They constitute a very interesting development from the small supply of ships and experience available at the beginning of the war.

A considerable number of British non-rigid airships were built and supplied to the French, Italian, Russian and American services, and one Italian semi-rigid was supplied to England for experiment. A large Astra ship of some 800,000 cub. ft. capacity was built in France with two large cars. It is understood that lack of longitudinal rigidity of the envelope gave trouble. The Italian airship design has favoured the semi-rigid type of construction, their most successful type being one in which the keel girder was not in itself rigid but " vertebrate," consisting of a number of pin-jointed frames capable of taking the longitudinal thrust induced by the car riggings, so long as the envelope held the keel in line. This system did not greatly reduce the height of the ship, as the points of attachment of the riggings were necessarily at the bottom of the envelope instead of near the level of its centre line. It did, however, enable a much lower envelope pressure to be used than in the non-rigids of the same size. This enabled a very light envelope fabric to be used and also a system of automatic pressure regulation by air taken at the nose of the airship. These ships were designed for bombing raids at great heights across the Adriatic Sea. The excellent weather conditions rendered their comparatively slow speed quite satisfactory.

Germany built a few large semi-rigids of the M type and the Parseval type. The two largest, PL26 and 27, were of some

1,120,000 cub. ft. capacity. They embodied many interesting features, including spherical partitions which divided the envelope into sections so that the accumulation of pressure at the upper end of the ship when pitched was avoided. As far as is known, no very thorough trial of these ships was made, but as far as the experiment was carried it appears to have been satisfactory. The type was not, however, proceeded with on account of the decision to concentrate on the rigid type.

Italy, after the Armistice, built a large semi-rigid “ Roma,” intended for transatlantic service.

An interesting aircraft which was developed experimentally as a counter to the Zeppelin raids was the airship-plane devised by Wing Comm. Usborne. A complete aeroplane was rigged under the envelope of an S.S. airship in such a way that, after patrolling at a great height, the envelope could be released and the aeroplane left free to deliver its attack. After several preliminary flights the first attempt to slip the envelope in flight failed on account, probably, of temporary loss of pressure in the envelope. The machine was partly released prematurely, and was damaged as it fell away; Wing Comm. Usborne and Wing Comm. Ireland were both killed. The former particularly was a most serious loss, as he had up to that time been mainly responsible for the exceptionally rapid airship development.

Kite Balloons.-The Drachen kite balloon, in the form originally used by Maj. von Parseval and Capt. von Sigsfeld in 1896, was used by the Germans immediately on the declaration of war for observation of artillery fire. Its value became at once apparent, and it was immediately copied by the Allies, very large numbers being made. The stability was, however, so poor that this type could only be used in fair weather, and accurate observation was often difficult. Capt. Caquot of the French army designed an improved arrangement of stabilizers. Three fins, one at the bottom of the tail and two 120° from it, were in the summer of 1916 ultimately adopted instead of the single fin of the Drachen and the string of parachutes which were necessary with it. Considerably improved stability was obtained, and there was an important increase of the dynamic lift which gave increased height. This type was generally adopted by the Allies for military use and worked well up to 6,000 feet. The same type of balloon was used by the navy, but was replaced by a similar one designed to resist higher wind speeds and capable of only 2,000 feet. This was used extensively by the fleet for gunnery observation and as a look-out for submarines. The balloon, being in continuous telephone communication with the captain of the ship, could transmit information more completely and rapidly than other aircraft. The balloons were also used in the ships protecting convoys, although it was sometimes contended that they acted as buoys to show the position of the convoy to a submarine which could thereby keep in touch at a safe distance during the day and deliver its attack at night. These naval balloons were capable of very high wind speeds, in one instance 80 knots being recorded.

An Italian A.P. type of balloon having a considerably smaller length to diameter ratio was adopted to give very great static lift in calm air. These were used for the apron defence against aeroplane attack. A line of balloons lifted to a height of some 15,000 ft. a horizontal cable from which hung thin vertical wires arranged to foul the wings of the hostile aircraft.

Airship Operations.-During the early days of the war French airships were employed for bombing behind the German line, but the damage to the ships, usually through gas leakage caused by shell and bullets, was so great that only a limited amount of work was done.

The Italian airships designed specially for bombing raids at very high altitude across the Adriatic obtained considerable protection from their height, and more useful results appear to have been achieved.

The Zeppelin raids over England were an interesting achievement from the airship point of view. So much of the effect of these raids was indirect, in the delays to munition work during raid nights, large amount of personnel and material retained for defence, and also in the psychological effect produced, that it is