HMA 25 Following the success of HMA No. 9, further ships were ordered by the Admiralty.

Along with the Vickers Company, three new contractors were required to produce rigid ships.

The Vickers Company had already proven themselves with the design and construction of No. 9 and were the only company with any experience of building a large ship.

Following the trials and design success of HMA No. 9, it was agreed that the Zeppelin threat had to be tackled head on; the Admiralty required more ships. There were initial problems at the Admiralty with regards to change of staff and also general opinion regarding rigid airships, as the successful non-rigid programme was expanding rapidly. However in June of 1915, along with the Vickers Company, three new contractors were selected to produce rigid ships.

The three new contractors were Beardmore, Armstrong and Whitworth and finally Shorts Brothers. All three companies were to become famous in the world of aviation. By October 1915 the drawings were approved and three ships were ordered. By December the pace of design and the requirement for big ships had increased dramatically and a further sixteen ships had been budgeted for by the Admiralty. All of these ships were to become known as the 23 Class, which were in effect stretched versions of the original No. 9.

The designs were seen in essence as modified versions of No.9, with an extra bay inserted in the middle of the ship. A gun platform was added to the top of the ship designed to take a two pound gun and two Lewis machine guns. The platform was surrounded by 18 inch sanctions carrying lifelines. These sanctions could be extended to double the height in order to carry a canvas windscreen. Three other Lewis guns were to be fitted at the extreme tail, in the control car further aft and on the top walking way.

The bomb load was to be greater than that of HMA 9 but none was actually specified. The ships each possessed an external keel, to the same pattern as the No. 9. The cabin being 45 feet long contain crew accommodation, a wireless room and a bomb room. From the keel further aft were three gondolas which were suspended below and accessible by open ladders. The ship gondolas also contained airtight buoyancy bags in case the ships had to alight on water. This was a technical requirement of all ships since HMA 1 - the Mayfly. With this rapid expansion of the requirement for airship production, there were a few problems in that so far, only one company had actually built a ship and hence had all the facilities.

In April 1916 the Government approved for a total fleet of 10, 23 class ships, but this was later modified in the light of further design technology available from Germany. The later ships becoming the R23X class and the R31 class.

The HMA 23 was the first to be completed, and hence the designation of the class of ships. There were a number of delays in the initial constructions and the ship was completed on 26th August 1917. Five weeks later the HMA 25 was completed and her tests gave almost identical results. Although not unexpected, the figures were disappointing and 2 weeks later on the 18th October the Admiralty decided that the design must be altered.

Some of these modifications had already been carried out on the first three ships, while others followed in due course. Together they effected a marked, if not substantial, improvement to the airships' performance. No 25 was delivered in the same month.

No 25 had been assembled slightly differently from the other three ships and always suffered from gasbag surging, which caused instability by moving the centre of lift unpredictably. In spite of this she flew 221 hours and 5 minutes in service, covering 5,909 miles. Stationed for most of her career at Cranwell, she was used mainly for training before being deleted in September 1919.