Engine-room telegraphs, swivelling propeller telegraphs, speaking tubes and telephones, with a lighting set for the illumination of the cars and keel, were all fitted in accordance with the practice standard in all rigid airships.

The lift and trim trials taken before the initial flight trials showed that the ship possessed a disposable lift under standard conditions of 5.7 tons. The original disposable lift demanded by the specification was 3 tons but this was reduced by 2 tons owing to the machinery weights being 2 tons in excess of the estimate. Since then these weights had been increased by another half-ton, making a total of 2 1/2 tons over the original estimate. It was evident that with so small a margin of lift these ships would never be of real use, and it was decided to remove various weights to increase the lift and to substitute a wing car of a similar type to those manufactured for the R 33 class for the heavy after car at present in use.

R 23 carried out her trials without the alteration to the car, which was effected at a later date, and the same procedure was adopted with R 24 and R 25. In the case of R 26, however, she had not reached the same stage of completion as the other two ships, and the alterations proposed for them were embodied in her during construction. The gasbags were of lighter composition, all cabin furniture was omitted and the wing car was fitted in place of the original after car. This wing car is of streamline shape with a rounded bow and tapered stern. The lower portion is plated with duralumin sheets and the upper part is covered with canvas attached to light wooden battens to give the necessary shape. This effected a very considerable reduction in weight. The original 250 horse-power Rolls Royce engine was installed, now driving a single large two-bladed propeller astern. A test having been taken, it was found that the disposable lift under standard conditions was 6.28 tons. It was therefore decided that all the ships of the class should be modified to this design when circumstances permitted. Speed trials were carried out under various conditions of running, when it was found that the ship possessed a speed of 54 1/4 miles per hour with the engines running full out.

To summarize the performances of these ships as we did in the case of No. 9, we find:

Speed:
Full 54 miles per hour
Normal =2/3 48 " " "
Cruising =1/3 33 " " "
Endurance:
Full 18 hours = 1,000 miles
Normal 26 " = 1,250 "
Cruising 50 " = 1,900 "

The production of the rigid airship during the war was always surrounded with a cloak of impenetrable mystery. Few people, except those employed on their construction or who happened to live in the immediate vicinity of where they were built, even knew of their existence, and such ignorance prevailed concerning airships of every description that the man in the street hailed a small non-rigid as "the British Zeppelin" or admired the appearance of R 23 as "the Silver Queen." The authorities no doubt knew their own business in fostering this ignorance, although for many reasons it was unfortunate that public interest was not stimulated to a greater degree. In the summer months of 1918, however, they relented to a certain extent, and R 23 and one of her sister ships were permitted to make several flights over London to the intense delight of thousands of its inhabitants, and a certain amount of descriptive matter appeared in the Press.

From that time onwards these large airships have completely captured the popular imagination, and many absurd rumours and exaggerations have been circulated regarding their capabilities. It has been gravely stated that these airships could accomplish the circuit of the globe and perform other feats of the imagination. It must be confessed that their merits do not warrant these extravagant assertions. The fact remains, however, that R 23 and her sister ship R 26 have each carried out patrols of upwards of 40 hours duration and that, similarly to No. 9, they have proved of the greatest value for training airship crews and providing experience and data for the building programme of the future. At the present time highly interesting experiments are being carried out with them to determine the most efficient system of mooring in the open, which will be discussed at some length in the chapter dealing with the airship of the future.

RIGID AIRSHIP 23 X CLASS

During the early days of building the airships of the 23 class, further information was obtained relating to rigid airship construction in Germany, which caused our designers to modify their views. It was considered a wrong policy to continue the production of a fleet of ships the design of which was becoming obsolete, and accordingly within ten months of placing the order for this class a decision was reached that the last four ships were to be altered to a modified design known as the 23 X class. As was the case with the ships of the preceding class when nearing completion, they were realized to be out of date, and special efforts being required to complete the ships of the 33 class and to release building space for additional larger ships, the construction of the second pair was abandoned.

The main modification in design was the abolition of the external keel, and in this the later Zeppelin principles were adopted. This secured a very considerable reduction in structural weight with a corresponding large expansion of the effective capabilities of the ship.