Airship Heritage Trust
Click here to return home 




Coastal Class
Coastal Class and C * Class

As the war progressed, and the designs of the raiding Zeppelins improve, so did the design and performance of the British Coastal defense airships. The “SS” Class ships had proved not only a deferent and protection for submarines, but they could also engage the enemy threat as well. A larger ship was therefore required with a bigger bomb load, and longer airborne duration. The “Coastal” Class was born..

Statistics
Coastal Class
C* Class
Length
195.6ft
217 ft
Diameter
37ft
49.3ft
Height
52ft
56ft
Speed
52mph
58mph
Engines
2 x 150hp (various engine configurations)
Forward 110hp Berliet; aft 220 Renault or 240hp Fiat
Volume
170, 000cft
210,000cf
Total Lift
4.94 tons
6.46 tons
Disposable Lift
1.6 tons
1.8 tons
Endurance
22 hrs
20 hrs
Documents
 
 
Photo Gallery
C.20 landing at East Fortune,Scotland in bright sunshine, showing the distinctive tri-lobe envelope design, and tail fin configuration

C.23A, a replacement for C.23, landing with the help of a ground handling party. C.23A was the last Coastal Class airship built.

A close up of the Coastal C.9 car which was based at RNAS Mullion in Cornwall. Notice earlier two bladed propellor have been replaced by 4 bladed, and then balloonet airscoop has been moved behind the rear engine to avoid obscuring the view of the crew as had been laid out on earlier configurations.
Coastal C.19 launching from in front of the metal shed at RNAS Kingsnorth.
Coastal Class C.46 on submarine and mine scouting patrol following a destroyer
Coastal Class on scouting patrol following a destroyer.
"Sky and Sails" by reknowned artist Barry Barnes, depicting a Coastal Class airship alongside a sailing schoner under full sail. (AHT Collection)
 
"The loss of the C.23A at sea" A watercolour paining showing the last moments of the last Coastal, C.23A lost at sea on 10th August 1918. Artist unknown but possibly one of the crew members (A Lawson Collection)
Despite the annotation noting the C.21 was "attacked by a German Submarine", the damage was caused when ship when leaving the ground for patrol. None of the crew were injured.
"Life in the old girl yet"
"Another spot of dismantling"
"Safely to bed" despite the ground crew handling the ship into the Capel Coastal shed, the gondola was damaged beyond repair and the ship deleted after 831 hours' flying.
C.27 being walked out of the Coastal shed at Pulham. The windbreaks on either side of the shed caused eddies and made ground handling very challenging.
The open cockpit for the crew positions. Seen here are the navigator position, the WT operator and rear engineer.
The crew of C.25 adapted the cockpit with an enclosed canopy for protection against nst the elements. This was the only example of a Coastal ship converted in this way.
 
A rare captured image of the C.27 envelope on fire after being attacked on 11th December 1917. Only one of two ships lost to enemy action.
C*7 Launching from the RNAS Longside Coastal shed. Notice the more elongated tail behind the control fins, compared to a Coastal Class ship envelope.

C*1 Coastal Star class airship with more elongated envelope.

A close up of the C*1 enclosed gondola, taken from the C.12 ship. Notice the additional viewing portholes and engine configuration with engines at both ends of the gondola.

The urgent need for a non-rigid airship to carry out antisubmarine patrol having been satisfied for the time with the production of the S.S. B.E. 2C type, the airship designers of the Royal Naval Air Service turned their attention to the production of an airship which would have greater lift and speed than the S.S. type, and, consequently, an augmented radius of action, together with a higher degree of reliability.

Demand for Protection

As the name "Coastal" or "Coast Patrol" implies, this ship was intended to carry out extended sea patrols within the vicinity of the coastline of the British Isles and main shipping lanes. With the losses to shipping convoys accelerating, by the summer of 1915 this need was becoming very pressing.The German U-boat force had primarily based itself in the port of Ostend in Belgium, giving the submarines better access to the sea lanes both the English Channel and up in to the North Sea, and therefore all around England.

The German Navy made use of this advantage, sending out a feet of nearly 20 U-boats to begin the naval blockade. In January 1915, before the declaration of "unrestricted submarine warfare" as the submarine blockade was called, 43,550 tonnes of shipping had been sunk by U-boats.

The number of sinkings then steadily increased, with 168,200 tonnes of shipping being lost in August 1915. Attacking without warning, German U-boats sank nearly 100,000 GRT per month, an average of 1.9 ships daily

Design

The design for a new ship fell on to the design team based at RNAS Kingsnorth who were sent with instructions from the Admiralty to create a new design of ship, but with use of existing equipment.

Using a French Astra Torres ungainly looking tri-lobed envelope and based on the French design, a new larger scouting ship was required to have a longer duration and heavier bomb load. Design and advancement on the envelope also progressed with an unusual “Tri-lobe” design. The Admiralty had already acquired two Astra Torres ships after the outbreak of the war. The first ship was originally designated No.8, and was commanded at various times by Commander Hinks and by Commander Usbourne. The No. 8 had an uneventful career before being deleted in May 1916. The second ship, was commissioned in early 1915, had been designated as No.10 and was almost immediately dismantled in order to serve as the basis of the new design, and her component parts were extensively modified in course of preparation.

This was seen as a stronger, more aerodynamic. Again, the use of existing technology was used to keep the costs down and production speeds up with demand. The gondola was based on two tail-less Avro shortened aeroplane fuselages connected end to end, and carried 2 engines in tandem. This produced a four or five seater car, depending on configuration or comfort of the crew.

The Tri-lobe envelope was 196 feet long and a capacity of 170,000 cft. The ridges in the envelope was connected to fabric curtains inserted to help maintain the shape. Four ballonets were also fitted, two in each of the lower lobes, and a single scoop consisting of a single sheet of aluminum tube of oval cross section reached down towards the forward propellor. Later versions of the ship had the scoop at the rear propellor. Single skids replaced the normal undercarriage and also protected the propellers. The rigging was also the same type as seen in an existing Astra Torres ship.

Armament

The Coastals were fitted with a larger bomb load than their predecessor ships, the SST class ship, also a wireless, and 2 machine guns, one of which situated on a small platform on the on top of the envelope. This gun positions was accessed by a tube and rope ladder from the gondola up inside the envelope and out through the top. The pressure of the gas was firm enough to hold a platform gun and gunner. Sometimes commented as the "ugliest" dirigibles ever made, these ships were reported by the crews as erratic and unstable in flight. The responsiveness in the controls was sluggish and often caused the crew to be airsick. However one of the main advances in airship technology was the very high rate of climb which the Coastals managed to provide.

Before the advent of later and more reliable ships, the bulk of anti-submarine patrol on the east coast and south-west coast of England was maintained by the Coastal class ship, in protecting the convoys and signaling to destroyers.

On the east coast of England, with the prevailing westerly and southwesterly winds, these airships had many long and arduous voyages on their return from patrol, and in the bitterness of winter their difficulties were increased ten-fold. To the wholehearted efforts of Coastal pilots and crews is due, to a great extent, the recognition which somewhat tardily was granted to the Airship Service.

The shape of the envelope is not all that could have been desired, for it is by no means a true streamline, but has the same cross section for the greater part of its length, which tapers at either end to a point which is slightly more accentuated aft. Owing to the shape, these ships, in the early days until experience had been gained, were extremely difficult to handle, both on the landing ground and also in the air. They were extremely unstable both in a vertical and horizontal plane, and were slow in answering to their rudders and elevators. This was to be later rectified in the C* (Coastal Star) class of ship.

The envelope was composed of rubber-proofed fabric doped to hold the gas and resist the effects of weather. Four ballonets were situated in the envelope, two in each of the lower lobes, air being conveyed to them by means of a fabric air duct, which was parallel to the longitudinal centre line of the envelope, with transverse ducts connecting each pair of ballonets. In earlier types of the Coastal, the air scoop supplying air to the air duct was fitted in the slip stream of the forward engine, but later this was fitted aft of the after engine.

Six valves in all were used, four air valves, one fitted to each ballonet, and two gas valves. These were situated well aft, one to each of the lower lobes, and fitted on either side of the rudder plane. A top valve is dispensed with because in practice when an Astra-Torres envelope loses shape, the tendency is for the tail to be pulled upwards by the rigging, with the result that the two gas valves always remain operative.

"Crabpots" valves and covers, so called for their shape resembled fisherman's crabpots, and non-return valves are employed in a similar manner to S.S. airships.

Astra-Torres Envelope and Rigging System

The Astra-Torres system of internal rigging is described in some detail as follows. The envelope is made up of three longitudinal lobes, one above and two below, which when viewed end on gives it a trefoil appearance. The internal rigging is attached to the ridges formed on either side of the upper lobe, where it meets the two side lobes. From here it forms a V, when viewed cross sectionally, converging at he ridge formed by the two lobes on the underside of the envelope which is known as the lower ridge.

To the whole length of the top ridges are attached the internal rigging girdles and also the lacing girdles to which are secured the top and side curtains. These curtains are composed of ordinary unproofed fabric and their object is to make the envelope keep its trilobe shape. They do not, however, divide the ship into separate gas compartments. The rigging girdle consists of a number of fabric scallops through which run strands of Italian hemp. These strands, of which there are a large number, are led towards the bottom ridge, where they are drawn together and secured to a rigging sector. To these sectors the main external rigging cables are attached. The diagram shows better than any description this rigging system.

Ten main suspensions are incorporated in the Coastal envelope, of which three take the handling guys, the remaining seven support the weight of the car.

The horizontal fins with the elevator flaps, and the vertical fin with the rudder flap, are fixed to the ridges of the envelope.

The Control Car

The car was evolved in the first instance by cutting away the tail portion of two Avro seaplane fuselages and joining the forward portions end on, the resulting car, therefore, had engines at either end with seating accommodation for four. The landing chassis were altered, single skids being substituted for the wider landing chassis employed in the seaplane. The car consists of four longerons with struts vertical and cross, and stiffened with vertical and cross bracing wires. The sides are covered with fabric and the flooring and fairing on the top of the car are composed of three-ply wood. In the later cars five seats were provided to enable a second officer to be carried.

The engines are mounted on bearers at each end of the car, and the petrol and oil tanks were originally placed adjoining the engines in the car. Various engines were used on the Coastal class. The most common configuration was two water-cooled Sunbeam engines, producing 150 hp each. Some replaced the aft unit with a Renault engine of 220 hp (164 kW), and various airships were deployed with a 100 hp Berliet engine in the front position. The former change was usually an attempt to improve the Coastals' leisurely top speed, whilst the latter was an attempt to improve reliability over the Sunbeam units, which had short lives when required to run at full speed for hours at a time in the long patrols undertaken by the airships.

A 1.5 horsepower (1.1 kW) ABC engine was mounted in the gondola. This drove a dynamo to power the radio and, if needed, an auxiliary ballonet blower

At a later date various methods of carrying the petrol tanks were adopted, in some cases they were slung from the envelope and in others mounted on bearers above the engines.

Wireless telegraphy is fitted as is the case with all airships. In the Coastal a gun is mounted on the top of the envelope, which is reached by a climbing shaft passing through the envelope, another mounting being provided on the car itself.

Bombs are also carried on frames attached to the car. Sunbeam engines originally supplied the motive power, but at a later date a 220 horse-power Renault was fitted aft and a 100 horse-power, Berliet forward. With the greater engine power the ship's capabilities were considerably increased.

Range

Exceedingly long flights were achieved by this type of ship, and those exceeding ten hours are far too numerous to mention. The moot noteworthy of all gave a total of 24 1/4 hours, which, at the time, had only once been surpassed by any British airship.


Launched in to Service: The C.1

The prototype ship, classed as C.1 entered undertook a first flight from RNAS Kingsnorth on 26th May 1915, which was to be applauded for the design team to come up with a flying prototype to the new specification in such a short time period.When she was brought out of her shed, it was seen that the C.1 initially had a yellow envelope that was not doped (or at least not doped in the same manner as other non-rigids).

No details of the first flight were recorded in the Daily Report for the Kingsnorth Station, however it was commented that the ship was unstable fore and aft owing to the original small Astra Torres horizontal fins which were fitted to the original envelope. A second flight was made on 31st May 1915, again no flight details were recorded in the Daily Report, however the comment was made that "at nearly hull (full) speed, nose of envelope blew in. More nose stiffeners added later"

The C.1 was little used for the rest of the year, one flight in June, two in July, one in August and two in September, with various modifications being made between each flight. After the last flight in September 1915, the C.1 was laid up until January 1916.

On 16th January 1916, the C.1 was handed over for further evaluation. The C.1 passed the initial tests and by the end of January completed her trials, and certification, leading to further orders being based on the same simple design to follow. The C.1 was launched with twin bladed propellors and as in later designs, this was changed to 4 bladed, along with further design changes.

After the trials, it was considered that the range could be extended by the possibility of refueling at sea, which would reduce the need to return to base, but also extend the patrol range. During the spring of 1916, C.1 was involved in experiments on 12th May, with being towed by the light cruiser HMS Carysforth out of Harwich, and then by HMS Canterbury. This was repeated again with success on May 16th, under the direction of Commodore R. Y. Tyrwhitt. The C.1 under took the experiment again with HMS Canterbury on 6th September 1916.

After many practice attempts, it became possible for the airships trail rope to be picked up at some 26 knots before speed reduced to 12 knots to allow the ship to be pulled down safely within 100 feet of the cruisers decks. From being in this "tow" position, a bosun's chair could be lowered with a member of the crew, to the deck, and a replacement crew member could be winched up to the airship. The ship could be refueled by pumping of petrol up by compressed air at a rate of 60 gallons in eight minutes.

Despite the success of the practice crew change and offshore refueling, these techniques were not widely used, but were in occasion enabled the Coastal Airships to accompany the Grand Fleet as scouts out of their existing range.

The C.1 was active during trials in 1916, and active again in 1917, but was laid up in February 1917 and not used again being deleted in June 1918 with only 90 hours flying time recorded.

Long-standing life of Coastal C.2

The record of one of these ships so deleted is surely worthy of special mention. Being first commissioned on 28th January 1916 she was in commission for 2 years 75 days, with hours flown of 2,273 hours, and averaged for each day of this period 3 hours 6 minutes flying. During this time she covered upwards of 66,000 miles. The ship was finally deleted from service in October of 1919, from this it will be seen that she did not pass her life by any means in idleness.

Coastal C.9 - Most Successful Service Life

The most successful ship in this class was the C.9 which flew from RNAS Mullion in Cornwall. The ship had a service flying life of 2,500 hours 11 minutes, some 68,201 miles, before being deleted from the active list on 1st October 1918. The C.9 patrolled the English Channel in all weathers and was often risky flown without ballast, in order to carry more fuel and bomb load. The C.9 was involved in many dramatic incidents and on several occasions successfully attacked German U-Boats.

Coastal C.24 - Longest Flight

The longest single flight recorded by a Coastal ship was 24 hours 15 minutes by C24 on 9th 10th July 1917

Coastal C.21 - Accidents do happen

Despite the annotation noting the C.21 was attacked by a German Submarine, the damage was caused by the ship when leaving the ground for patrol. On 1 June 1918, when launching, the forward handling guys hit the roof of a small hut and where whipped up in to the forward engine's propellor, causing a rent around 4ft long in the balloonet and a rent of 2ft long in the envelope.

The pilot immediately opened up the aft engine and turned back to the aerodrome at Folkstone, with the idea of landing as soon as possible. The airship managed to return to base at Folkstone but the loss of gas caused the envelope to collapse. The photos on the side of the page were captured in trying to get the damaged ship in to the shed.

The car was damaged beyond repair and the ship deleted after 831 hours' flying. Despite the ship having been on the station at Folkstone since February 1918, the C 21 had not been that successful on operations and had absorbed far more manpower than she was worth. After this accident, it was decided that the Capel / Folkstone RNAS base was to only run SS-Zero patrol airships.

Production of this class of ship ceased in 1916.

Only 2 were destroyed through enemy action in the entire war. In total 35 “Coastal” Class ships were built, however 12 were totally destroyed in some manner and only 4 survived to the Armistice.

Four Coastal Class ships (C.a-d) were sold to Russia in 1916, and one Coastal ship, the former C.4 was sold to the French Government.

Due to the size and often instability when landing or taking off, and often the inexperience of the ground handling crew for handling a larger airship than the smaller Submarine Scout class ships, many of the Coastal Class ships were accidentally lost.

Losses due to Enemy Action

Of all of the British airships produced during the First World War, two were destroyed due to enemy action during the entire war. Both of these losses were Coastals, the C.17 and C.27.

On 21st April, 1917 Coastal C.17 was captained by Sub-Lieutenant E.G.O. Jackson was was patrolling the Straits of Dover. The C.17 was engaged and then attacked by German aeroplanes. Despite fighting back using her machine guns, the airship stood no chance as was shot down within sight of several trawlers. Tragically all crew members were lost.

On 11th December 1917, Coastal C.27 commanded by Flight Lieutennant Dixon was shot down in similar circumstances as the C.17 enagement, this time being attacked by two Hansa-Brandenburg seaplanes, flying from their base on the other side of the English Channel from Zebrugge.

Both were shot down by German aeroplanes when they strayed too close to enemy-occupied territory. In both times, there were no survivors of the crew. It was unusual for these losses to occur to enemy action, as airships were normally safe from air attack, as they usually flew beyond the range of land based aircraft. and no zeppelins were ever sent to intercept them.

Towards the end of 1917, these ships, having been in commission for over two years, were in many cases in need of a complete refit. Several were put in order, but it was decided that this policy should not be continued, and that as each ship was no longer fit for flying it should be replaced by the more modern Coastal known as the C Star.

 

Coastal C* Ships

The RNAS Kingsnorth design team took upon themselves to correct the earlier design problems encountered with the Coastal class ship, and the crew feedback regarding the instability of the ship on takeoff and landing. In changing the control surfaces and making a more streamlined tail to the envelope, these stability problems were corrected.

The second class of “Coastal” were designated the “C*” (C Star) Class. Due to the technical problems which were being encountered at RNAS Kingsnorth with the development of the larger North Sea Class ships, it was decided that an interim class of ship was needed. With this saw the improvement of the Coastal Class ship, and the development of the C Star airship class.

The control car of the C* class ship was similar to that of the existing Coastal Class ship, and indeed the prototype C* ship took the existing control car from the C.12. The C* ships retained the open cockpits but extended engine mounts were put at the rear, and the body was covered with plywood instead of fabric. In order to improve observation, four circular portholes of Triplex glass were provided for on either side of the car, and another placed on the floor of the pilots compartment. The feedback from the crews on the Coastal Class ship were incorporated in improving of the overall comfort of the car for the crew.

The main alteration, which was more recognizable was the change to the envelope. The common Astra Torres trilobe form was retained, but the length was increased to 207 feet and increasing the capacity to 210,000cft. The shape of the envelope became much more streamlined and graceful compared to the original Coastal Class envelope. This was a development project, and so the first three ships of the C* Class still had rather a blunt stern tip.

The later ships had more of a slender tail with increasing the length of the tail by another 10ft, but without adding to the overall capacity. To improve control, and stability, six balloonets were fitted, two large one amidships, two smaller once forward and another two aft. Each pair was connected by a tube., while the three starboard balloonets were further interconnected by the air delivery duct, which lead from the airscoop positioned to collect air from the slipstream of the after engine. The duct was fitted externally at first but was later placed inside the envelope in order to improve streamlining.

The Coastal "Star" class ship enjoyed more powerful and reliable engines, with the aft engine being changed to 220hp water cooled Renault engine, whilst the forward engine was a 110hp water cooled Berliet engine. On later models the Renault engine was replaced by a water cooled 240hp Fiat engine. Unlike the Coastal Class ships, there was no gunner position on the top of the envelope, so this saved some 250lb in weight, and allowed a gas release valve to be placed in the same position, but a pair of Lewis guns were carried in the control car, which also had fittings for two 230lb and two 100lb bombs. For the crew, five parachutes were also carried, the lines of which could be attached quickly to a harness worn at all times by each crew member.

Although the rate of climb on a C* ship, was not as fast as a Coastal class ship, the new ships proved to be superior in every other way and capable of a top speed of 56mph.

10 C * airships were completed and put in to operation, however they were not regarded as entirely successful as 20 were originally ordered, and production at RNAS Kingsnorth was discontinued in favour of the SS Twin Sea Scout airship, after the first 10 had been delivered between February to July 1918.

The C* airships had rather uneventful careers compared to those of the Coastal Class ships, as they came late in on to the scene of the war, and all carried out long and regular patrols carrying out their duties efficiently without incident. The longest continuous flight recorded was of 34 hours and 30 minutes by C84 commanded by Captain Cleary on 27th to 28th May 1918.

Torpedo Launching and Flying Ambulances

A project came under discussion in the latter part of the war, and to better hunt the submarine threat, was to equip all the C* airships with torpedoes. As the enemy submarines frequently submerged no further than periscope depth, with was decided to experiment with launching circling torpedoes, designed to be run in descending spirals, before finding the target. The end of the war prevented the plan from being furthered.

A second proposal was the modification of the C* design and due to it's extended range, was to use the ships as flying ambulances. The idea being that the airship would have brought urgent medical cases from the Western Front, directly to England, escorted with aeroplanes. Again the proposal made in January 1918, was never fully investigated or implemented.

End of the series

The Coastal airship played no small part in the defeat of the submarine, but its task was onerous and the enemy and the elements unfortunately exacted a heavy toll. A German wireless message received in this country testified to the valiant manner in which one of these ships met with destruction. Despite being rushed in to production, having to fulfill a role which was unprepared, they gave valuable experience to design teams, ground crews and flight crews during testing times of war. It cannot be ignored that the Coastal Class ship was designed at a time of severe pressure during the war, and can be seen as a jump from the previous Submarine Scout class, and therefore very well conceived. The losses of the Coastal class ship, seemingly more than any other class of ship, needs to be seen as a combination of a fair share of disasters, caused by combinations of inexperience, and some genuine and often overlooked bad luck. Operational difficulties can also be linked with the conditions in which the crews were put to work, with very bad weather over the North Sea and Western Approaches. It has to be applauded that these workhorses were the only airships available to protect the East Coast commercial shipping for the whole of 1916 and the most of 1917. Despite the losses and accidents many of the ships were often reused and became redeveloped in to the new class of Coastal Star ship.

The improvements lead to the redesign of and development of the C* ships, and the record of the C* ships were quite extraordinary in comparison, as none caught fire, was wrecked, lost at sea or destroyed in any way. From the logs, none appear to have been destroyed in any way or noteworthy incident, and all were still active at the time of the Armistice, with all 10 ships being deleted in October of 1919.

Related ships: Submarine Scout, North Sea Class

Copyright © 2021 Airship Heritage Trust. All Rights Reserved. Copying and/or redistributing of any files is illegal under international copyright law. AHT is not responsible for the content of external sites.