1) Mayfly were agreed by the Committee for Imperial Defence in early 1913,[2] and that Vickers should be asked to design an improved class of ship incorporating all that was then known about the Zeppelins.

Pratt in turn hired Barnes Wallis, whom he had met while both were working for the shipbuilding firm of J. Samuel White, as his assistant.

[4] The initial order for the new ship was placed on 10 June 1913, with the final plans being agreed at the end of the year, and a formal contract was signed in March 1914.

In addition there was a radio cabin and a mess space for the crew within the keel structure, which also contained the fuel and ballast tanks.

Difficulties were encountered with the fabrication of the duralumin girders for the transverse frames, and there were many changes to the design, including strengthening the hull so that it could be handled safely by inexperienced crews, and replacing the original drive arrangement of paired propellers mounted on the sides of the hull with swivelling propellers mounted on the gondolas (as used on contemporary British Army dirigibles).

[3] On 19 June 1915, after Churchill had been replaced as First Lord by Arthur Balfour, a conference was held at the Admiralty to consider all airship development.

However, resumption of work was delayed by the necessity to retrieve Pratt and Wallis who had enlisted in the Army when construction was cancelled.

[10] No.9r was then sent to the RNAS airship station at Howden in the East Riding of Yorkshire where it spent most of the time being used for experimental mooring and handling tests.