The 23X class was a development of the 23 class, itself often seen as merely an improvement to the No 9 design, however there were some radical changes and lessons learnt. Four of the class were originally planned, with numbers running consecutively from R.27 to R.30, but following the downing of the L-33 virtually intact, the British were able to re-think the programme and hence R.28 and R.30 were cancelled in order to concentrate resources on the new R.33 class.

R.27 and R.29 differed from their predecessors in that minor modifications to the shape of the hull had given them slightly more gas capacity, but more important was the elimination of the external keel corridor. The function of this feature was primarily to distribute the weight of fuel tanks, ballast bags and similar items, and only secondarily to strengthen the hull, so its absence in the two 23X ships was intended to effect a considerable saving of weight without causing any significant loss of strength and also to improve manoeuvrability. The various loads were concentrated at the bulkheads and suspended from the radial wiring which maintained the hull in its correct polygonal shape.

Compare the 23 Class with the 23X Class.

Graphic copyright N Regamey

An internal corridor which allowed the crew to travel between the cars was formed by inverted U-shaped ribs positioned above the two lowest longitudinal girders, the surrounding gasbags being appropriately shaped. The corridor also gave access to the ballast bags and petrol tanks. The latter were interconnected by a long, wide aluminium tube running underneath them, an arrangement which helped with refuelling and could be used in an emergency to jettison fuel.

The four engines were again Rolls Royce Eagle V12 designs, but they were the later Series 6 models, which produced 300 hp at full revolutions. The engine arrangement was the same as that used originally for the 23 class ships, with pairs of swivelling propellers in the forward and after gondolas and twin engines driving fixed propellers in the midship car. The radical and original decision to do without a normal keel was fully vindicated when the first trials were held. Not only were the two airships able to turn more quickly than their forerunners, but the real benefit was found when the lift and trim tests were held; the disposable lift was more than 8 1/2 tons, much better than any previous British airship and allowing a more effective bomb load to be carried as well as sufficient fuel for extended cruising. One handicap common to both ships, as well as to their predecessors, was the absorbent nature of the hull's outer covering of doped linen; a few hours of rain could add around a ton of water to the weight.

R27

R.27 was commissioned on 29th June 1918, and flew 89 hours 40 minutes in service commanded by Major Ommaney before coming to a disastrous end. On 16th August she was in the hangar at Howden at the same time that some riggers were helpfully trying to make a new airship by attaching a spare SS Zero car to a disused envelope. While they were completing the job some petrol was spilt into the car; it was not mopped up. The spilt petrol was ignited a little later by a spark when an unsuspecting operator came to test the WIT equipment. The flames, fed by both fuel and gas, expanded within seconds into a conflagration that totally destroyed not only the makeshift blimp and R.27, but also SSZ.38 and SSZ.54, which had been moored nearby. The hangar itself survived, although badly damaged. One airman who failed to get out in time lost his life.

Shown here is the R27 in Howden shed with 3 Coastal class ships before the fire.

R 29

R.29 was a more fortunate craft in every way and the most successful wartime rigid, being the only one to meet enemy action. She was commissioned on 20th June 1918, based at East Fortune and in a brief operational career of less than five months flew 335 hours and covered an estimated 8,215 miles. Once she carried out a patrol of over 30 hours, twice more she made a flight longer than 20 hours and three times she encountered German U-boats. The first escaped, the second ran on to a mine and only the last was attacked. On Sunday 29th September, at about half past one in the afternoon and in exceptionally calm conditions, R.29, captained by Major G. M. Thomas, was escorting a convoy bound for Scandinavia when a faint patch of oil was seen discolouring the water near Newbiggin Point. A message, "Oil patch rising below me," was signaled by Aldis lamp to HMS Ouse, one of the escorting destroyers, which turned at once to help. Her captain could not see the slight evidence that was apparent to the airmen high overhead and he signalled for more information, "Drop light over it." In reply the airship indicated the probable whereabouts of the submarine by dropping not a flare but a 230 lb bomb, the destroyer joining in the attack with two depth charges as the first explosion subsided. Then R.29 dropped a second bomb and a calcium flare to mark the position of the oil patch, at which point another destroyer, HMS Star, joined with Ouse and two armed trawlers to add more depth charges to the barrage. At half past two, HMS Star reported considerable quantities of oil rising to the surface. She was commissioned on 20th destroyers then steamed off after the convoy. A buoy was placed as a marker by one of the trawlers and a deep depth charge was dropped, while R.29 remained on watch for more than an hour. When she at last left to rejoin the convoy at four o'clock large amounts of oil were still bubbling to the surface. It was subsequently confirmed from intelligence reports that UB.115 had been destroyed in the attack.

It was the sole success recorded by any British wartime rigid. After the Armistice R.29 flew another 16 hours before May 1919, when her midship car was replaced by a smaller and lighter type containing only one engine driving a single propeller. In this modified form she flew a further 87 hours, including a flight in June over Edinburgh, Berwick, May Island and the Firth of Forth, when she was accompanied by R.34. She was finally deleted in October, 1919, having covered an estimated 11,334 miles in service, more than any other British rigid up to that time.