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.

However to help the programme Vickers provided components to the other three companies to assist in production. The original ships were divided out between the various contractors and the registrations were allocated between them:-

H.M.A 23 - Vickers
H.M.A 24 - Beardmore
H.M.A 25 - Armstrong Whitworth
H.M.A. R26 - Vickers


HMA 23 Grpahic copyright N.Regamey

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. This led to the order of the R26 as Vickers had the space available to build the ship. On lift and trim trials, the HMA 23 was found to have a disposable lift of only 5.7 tons due to the machinery being two tons heavier than originally estimated. 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. On the day of the decision the HMA 24 was also tested and found to be mysteriously two thirds of a ton heavier than her sister ships, with a lift of only 5.1 tons. The alterations to the ships included the removal of dynamos and bomb frames and many other items which were deemed not necessary were removed. Upon inspection of No. 24 it was later found that the ship was heavier due to having used rivets, fastenings and bracing pieces which were slightly larger and heavier than originally expected and hence increased the overall weight of the ship.

The Admiralty ordered that modifications be carried out at once to R.26, which was still in the early stages of construction, while the other three ships were to be modified similarly but, of necessity, over a longer period and slightly less drastically. The measures to be undertaken were aimed at lightening the airships by the elimination of all unnecessary weight. In addition to removal of the dynamos, buffer wheels and bomb frames, many other small items not considered essential were either taken out or replaced with lighter equipment. The folding tables which had been intended for the keel cabin were never installed and the original plan of fitting a two-pounder gun on the top platform was also discarded. The rear car was replaced by a smaller and lighter one containing an engine with direct drive to a single two-bladed propeller 13 feet 6 inches in diameter. As there was now no space for the auxiliary controls, these were transferred to the keel cabin.

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 24 required more than minor modifications, since she was so much heavier than the other ships. As Beardmore's shed was needed immediately for the building of R.34, it was necessary to move the ship to her new station at East Fortune as soon as possible. This required extra lift to enable her to fly safely over the hilly countryside of southern Scotland, so in addition to the changes already made, the drastic step was taken of removing all the machinery from the aft car: engine, propeller, radiator and silencers. All these modifications brought the disposable lift up to nearly 6.5 tons, but the price paid was a top speed barely in excess of 35 mph. In this form No 24 was delivered in October 1917. No 25 was delivered in the same month, but R.26, on which Vickers could not begin work until No 9 had left Barrow, arrived much later. All the recommended modifications were incorporated in the course of her construction. Although built more quickly than the others, in only about a year, she did not fly until March 1918.

HMA No 23

All four of the 23 class airships were flown extensively, but although rather more efficient than No. 9 they still did not provide the performance which had been hoped for. No 23 herself had been commissioned on 15th October 1917, and left on that day for Pulham. She had a top speed of 52 mph and flew a total of 8,426 miles in 321 hours and 30 minutes. Although she carried out some patrols, usually under the command of Captain I. C. Little, she was used mainly for training and experimental work. Trials were undertaken in January 1918, at Pulham with a two-pounder gun in its mounting on the top platform of No 23. The gas valves were placed on either side of the hull rather than at the top to, avoid risk of escaping gas being ignited during firing.

Six shells were fired with the gun pointing downwards, but instead of embedding themselves in the mud of the airfield as expected, they seem to have ricochet into the surrounding countryside. The airship took the strain well, although some flexibility was present which would have adversely affected aiming under combat conditions. No further action was taken in the matter because of the ever present weight problem. Later in 1918, No 23 was involved in another experiment, this time to determine whether an aeroplane could be carried by an airship and released in mid-air either to repel attackers or to take offensive action on its own account. A Sopwith Camel was suspended beneath the envelope by specially prepared slings. For the first trial, a dummy was placed in the cockpit and the controls were locked. As the airship flew over Pulham air station the aeroplane was released. It glided to the ground, showing that the slipping gear operated correctly. Another Camel was then taken up, this time piloted by Lieutenant E. Keys. As the aeroplane left No 23 the pilot had no trouble in starting the engine. He pulled out of the dive to fly around the airship before landing safely.

No provision had been made for retrieval of the aeroplane during flight, as the intention was that it should make its own return to base after action. As with other unusual projects tried out during the war, nothing further was attempted. Similar trials were held after the war with R.33, and the method was eventually perfected by the Americans in the early 1930s. A noteworthy departure from routine training and testing befell No 23 on 6th December 1917, when she was sent to make an unannounced daylight flight over London, arriving out of the mist from Pulham around midday. At a low altitude she circled over Buckingham Palace, Whitehall and the City, where thousands of Londoners clearly saw the lights twinkling in her gondolas; the red, white and blue roundels on her envelope and her designation numerals. Wartime censorship allowed press reports of the incident ("At last. ..a British Zeppelin"), but the airship's number could not be published, despite its having been so publicly displayed! Twice in the following year No 23 flew again over London, on one occasion accompanied by R.26, but these appear to have been the high points in an otherwise mundane and unwarlike career. She was deleted in September 1919.

HMA No 24

Her sister ship No 24 had a similar history, flying a total of 164 hours and 40 minutes and covering 4,200 miles, but as the original intention of replacing her missing engine in a new and lighter car was never carried out, she remained very slow.

On one typical occasion, encountering an unexpectedly strong adverse wind near the Bass Rock, she remained for some time stationary, quite unable to make any headway. Despite this severe handicap she was used for training and convoy duties when conditions were deemed suitable, although she appears to have seen no action. She made her last wartime flight in June 1918, but was retained in service and two months later had her bows strengthened to adapt her for mooring trials at Pulham, where Vickers were building a new type of high mast.

The tests, which were carried out with both midship engines removed, were quite successful but were not completed finally until November 1919. The following month No 24 was deleted and scrapped.

HMA No 25

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.

HMA R 26

The last of the class was R.26. (The Admiralty decided on 18th December 1917, that all future rigid airships should have the prefix R before their number.) Apparently the only one of her class to incorporate all the design changes, she was commissioned on 22nd April 1918, and stationed at Howden. During tests she was found to have a disposable lift of 6 1/4 tons, a top speed of 54 mph and a ceiling of 3,500 feet. It was also discovered that if the engines were stopped at 53 mph the speed fell to 18 mph in two minutes, so great was the drag. By the end of the year she had flown 191 hours and 29 minutes, of which the highlights were a flight with No 23 over London on 25th October and a patrol of 40 hours 40 minutes on 4th/5th June, when she was commanded by Major T . This was the longest flight yet by a British rigid, beating No 23's previous record, set up a few days earlier, by 32 minutes. Later in the year she was transferred to Pulham and, commanded by Major Watt, she supervised the surrender of German submarines at Harwich on 20th November 1918. In January 1919, R.26 flew a further 6 hours 18 minutes, and then had her bows specially strengthened before being experimentally moored out in the open, using the "three wire system". She had a tendency to assume a tail up attitude, But this was overcome by fastening sandbags to the after guys, and she survived for over a week without harm. Then the weather worsened, rain soaked her envelope and a snowstorm finally beat her into the ground. Her cars were removed, allowing her to float again, but it was soon found that the damage she had sustained was too severe for repairs to be worthwhile. On 24th February the order was given for her to be scrapped and her official deletion followed on 10th March.