*British Astra-Torres.* A number of comparatively small Astra-Torres dirigibles have also been built in Great Britain for coast patrol and anti-submarine work. The line drawing at the left of Fig. 21 illustrates the general design and construction of these small airships, while the various letters indicate the different parts of the gas container, air balloonets, suspension and car, and the end view at the right of the figure shows the small amount of head resistance offered by the suspension of this type as compared with that of the usual form of nonrigid dirigible. _A_ is the balloon itself, or main gas container, the pressure relief valve for which is located at _M_. _BB_ are the air balloonets connected with the blower _H_ in the car. In the illustration these balloonets are shown fully inflated as they would be after the gas bag had lost a considerable proportion of its original contents through leakage or expansion. At the beginning of a flight, when the gas bag is fully inflated with hydrogen, they lie perfectly flat along the lower side of the envelope, being brought into service only as they are needed to keep the envelope distended to its full volume.
The novel method of suspension to which this type of dirigible owes its greater speed and fuel economy, because of the reduction of the head resistance, is shown by the numerous supporting ropes _O-O-O_, which terminate in a comparatively few cables attached to the car. In the small British airships referred to here, there is but one small car designed to carry a crew of two men and the engine is of comparatively low power, driving a propeller at either end of the car, but in the large French dirigibles of the same type, two large cars are placed tandem some distance apart and are fitted with 500-horsepower motors. The various parts indicated by the letters are: _CC_ propellers, _D_ motor, _F_ space for pilot and crew, _G_ fuel and oil tanks, _J_ guide rope, _K_ gas valve, _LL_ air valves, _NN_ balloonet cable, _P_ rudder, _Q_ stabilizer, _RR_ bracing cables, and _S_ the car itself.
*Limitations of Use.* Nothing excites the Teutonic imagination so strongly as things military to which the characteristic German adjective _kolossal_ can be enthusiastically applied. It was for this reason that, despite its uniform record of tragic disaster for years before the war, the Germans pinned their faith to the Zeppelin as a weapon that could not fail to strike terror to the hearts of the British and French and make them hasten "to sue for peace." However, apart from its reputed employment on the single occasion that the German grand fleet left the security of the Kiel Canal, it is not known to have been used in any purely military operation. The aeroplane has been developed to a point that, in spite of the ability of the Zeppelin to ascend rapidly when hard pressed, would make it suicidal for one of the huge gas bags to sally forth in daylight, unless attended by a large number of battle planes to prevent enemy flying machines from attacking it. No such use of the Zeppelin has been recorded thus far. Consequently, it has been used only in nocturnal bomb-dropping expeditions, chiefly directed against London and only undertaken when weather conditions made detection difficult. In order to carry these out, it has been necessary to establish stations in Belgium, since the fuel consumption of the Zeppelin is so great that, even with its tremendous fuel supply of 3 to 5 tons, a flight to London and return to points well within the German border is impracticable. The first raids of this character were carried out successfully, but subsequent attempts were marked by the loss of one or two airships on each occasion, so that the practice was abandoned as being too expensive for the results attained and aeroplanes were substituted.