Coastal class blimp
The Coastal Class (often known as the C-Class or simply the 'Coastals') were a class
Ship class
A ship class is a group of ships of a similar design. This is distinct from a ship-type, which might reflect a similarity of tonnage or intended use. For example, the is a nuclear aircraft carrier of the Nimitz class....

 of blimp
A blimp, or non-rigid airship, is a floating airship without an internal supporting framework or keel. A non-rigid airship differs from a semi-rigid airship and a rigid airship in that it does not have any rigid structure, neither a complete framework nor a partial keel, to help the airbag...

 used by the Royal Naval Air Service
Royal Naval Air Service
The Royal Naval Air Service or RNAS was the air arm of the Royal Navy until near the end of the First World War, when it merged with the British Army's Royal Flying Corps to form a new service , the Royal Air Force...

 (RNAS) during World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

. The C class blimp operated by the United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...

 after the war was a completely unrelated design. In total 35 Coastals were built, all at RNAS Kingsnorth
RNAS Kingsnorth
RNAS Kingsnorth was a First World War Royal Navy air station for seaplanes and airships, mainly operating as an experimental and training station, but also providing anti-submarine patrols...

, Kent
Kent is a county in southeast England, and is one of the home counties. It borders East Sussex, Surrey and Greater London and has a defined boundary with Essex in the middle of the Thames Estuary. The ceremonial county boundaries of Kent include the shire county of Kent and the unitary borough of...

. Entering service in 1916, the Coastal class remained in widespread service until 1918, with a few members of the class still in service at the signing of the Armistice
Armistice with Germany (Compiègne)
The armistice between the Allies and Germany was an agreement that ended the fighting in the First World War. It was signed in a railway carriage in Compiègne Forest on 11 November 1918 and marked a victory for the Allies and a complete defeat for Germany, although not technically a surrender...

, while others were replaced by the improved C-Star class
C-Star class blimp
-References:* London, P. U-Boat Hunters: Cornwall's Air War 1916-19 Dyllansow Truran, Truro. ISBN 1-85022-136-9-External links:*...

 as they became unfit for service. The blimps were used for long anti-submarine
Anti-submarine warfare
Anti-submarine warfare is a branch of naval warfare that uses surface warships, aircraft, or other submarines to find, track and deter, damage or destroy enemy submarines....

 patrols in the Western Approaches
Western Approaches
The Western Approaches is a rectangular area of the Atlantic ocean lying on the western coast of Great Britain. The rectangle is higher than it is wide, the north and south boundaries defined by the north and south ends of the British Isles, the eastern boundary lying on the western coast, and the...

 and English Channel
English Channel
The English Channel , often referred to simply as the Channel, is an arm of the Atlantic Ocean that separates southern England from northern France, and joins the North Sea to the Atlantic. It is about long and varies in width from at its widest to in the Strait of Dover...

, protecting convoys from German U-Boat
U-boat is the anglicized version of the German word U-Boot , itself an abbreviation of Unterseeboot , and refers to military submarines operated by Germany, particularly in World War I and World War II...

s. The Coastal class was one of the first aircraft types specifically designed to detect and attack submarines.

History & design

The C-Class was far from a new design. The prototype was built in 1915 by using the envelope
An aerostat is a craft that remains aloft primarily through the use of buoyant lighter than air gases, which impart lift to a vehicle with nearly the same overall density as air. Aerostats include free balloons, airships, and moored balloons...

 from the No. 10 Astra-Torres airship
Astra-Torres airship
The Astra-Torres airships were non-rigid airships built by Société Astra to a design by Spaniard Leonardo Torres Quevedo in France between about 1908 and 1922. They had a highly-characteristic tri-lobed cross-section rather than the more usual circular cross-section. This was the result of moving...

, and a gondola built using the front-sections of two Avro
Avro was a British aircraft manufacturer, with numerous landmark designs such as the Avro 504 trainer in the First World War, the Avro Lancaster, one of the pre-eminent bombers of the Second World War, and the delta wing Avro Vulcan, a stalwart of the Cold War.-Early history:One of the world's...

 seaplane fuselage
The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...

s joined together back-to-back to provide one tractor-
Tractor configuration
thumb|right|[[Evektor-Aerotechnik|Aerotechnik EV97A Eurostar]], a tractor configuration aircraft, being pulled into position by its pilot for refuelling....

 and one pusher
Pusher configuration
In a craft with a pusher configuration the propeller are mounted behind their respective engine. According to Bill Gunston, a "pusher propeller" is one mounted behind engine so that drive shaft is in compression...

Propeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...

. The envelope was composed of rubber-proofed fabric that was also doped to hold the gas and resist the effects of weather, and had a distinctive trilobe shape in which the two lower lobes were situated side-by-side, and the third was positioned centrally above them.

Sometimes referred to as the "ugliest" dirigibles ever made, production Coastals looked very similar, but used a bespoke gondola with canvas sides built over a wooden frame. The trilobe envelope allowed the gondola to be hung closer to the envelope, reducing the overall height of the aircraft and slightly reducing head resistance. Four ballonet
A Ballonet is a air-filled flexible container that is located inside the envelope of a non-rigid or semi-rigid airship. Such an airship can have one or more ballonets, commonly one fore and one aft...

s, two in each of the two lower lobes, were used to maintain the envelope's shape and pressure. These were kept inflated by a metal air scoop mounted in the slipstream of the forward propeller on earlier examples, and at the rear propeller on later versions. The nose of the envelope was made of aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 sheet reinforced with bamboo
Bamboo is a group of perennial evergreens in the true grass family Poaceae, subfamily Bambusoideae, tribe Bambuseae. Giant bamboos are the largest members of the grass family....

 canes to prevent it deforming due to the airflow pressure as the airship moved. Three tailfins were used. The two upper ones were mounted in a shallow V-tail
In aircraft, a V-tail is an unconventional arrangement of the tail control surfaces that replaces the traditional fin and horizontal surfaces with two surfaces set in a V-shaped configuration when viewed from the front or rear of the aircraft...

 configuration and carried the elevators
Elevator (aircraft)
Elevators are flight control surfaces, usually at the rear of an aircraft, which control the aircraft's orientation by changing the pitch of the aircraft, and so also the angle of attack of the wing. In simplified terms, they make the aircraft nose-up or nose-down...

, while the single vertical fin below the envelope incorporated a rudder
A rudder is a device used to steer a ship, boat, submarine, hovercraft, aircraft or other conveyance that moves through a medium . On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane...

. Ten main suspensions were incorporated in the Coastal envelope, of which seven supported the weight of the gondola, and the remaining three took the guys
A guy-wire or guy-rope, also known as simply a guy, is a tensioned cable designed to add stability to structures . One end of the cable is attached to the structure, and the other is anchored to the ground at a distance from the structure's base...

 that allowed the 196 ft (60 m)-long airships to be handled on the ground. No landing gear was fitted, apart from two wooden skids at either end of the gondola which also protected the propellers.

Various engines were used on the Coastal class. The most common configuration was two water-cooled Sunbeam engines, producing 150 hp
Horsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...

 (111 kW) each. Some replaced the aft unit with a Renault
Renault S.A. is a French automaker producing cars, vans, and in the past, autorail vehicles, trucks, tractors, vans and also buses/coaches. Its alliance with Nissan makes it the world's third largest automaker...

 engine of 220 hp (164 kW), and various airships were deployed with a 100 hp (74 kW) Berliet
Berliet was a French manufacturer of automobiles, buses, trucks and other utility vehicles, based in Vénissieux, outside of Lyon, France.-Early history:...

 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
ABC Motors
ABC Motors Limited of Hersham, Surrey, England was a manufacturer of cars, aircraft, motor scooters, and engines for road and air. Established by Ronald Charteris in Hersham, Surrey in 1912, its chief designer was the young and talented Granville Bradshaw...

 engine was mounted in the gondola. This drove a dynamo
- Engineering :* Dynamo, a magnetic device originally used as an electric generator* Dynamo theory, a theory relating to magnetic fields of celestial bodies* Solar dynamo, the physical process that generates the Sun's magnetic field- Software :...

 to power the radio and, if needed, an auxiliary ballonet blower.

The standard layout was to carry two 110-gallon (500 litre) fuel tanks, one per engine. These were usually mounted within the gondola, but when using the non-standard engines, the tanks would sometimes have to be relocated to outside the gondola or even hung from the rigging. Other equipment carried in the gondola included the compressed-air tanks for the engine starters, the engine oil tanks and the sandbag ballast.

There was no standard armament for the class. The most usual set-up consisted of at least two .303
.303 British
.303 British, or 7.7x56mmR, is a .311 inch calibre rifle and machine gun cartridge first developed in Britain as a blackpowder round put into service in December 1888 for the Lee-Metford rifle, later adapted to use smokeless powders...

 Lewis guns
Lewis Gun
The Lewis Gun is a World War I–era light machine gun of American design that was perfected and widely used by the British Empire. It was first used in combat in World War I, and continued in service with a number of armed forces through to the end of the Korean War...

. These could be mounted in a variety of places around the gondola. Another Lewis Gun was mounted on a Scarff ring
Scarff ring
The Scarff ring was a type of machine gun mounting developed during the First World War by Warrant Officer F. W. Scarff of the Admiralty Air Department for use on two-seater aircraft...

 on the top of the envelope to provide a token defence from attacking aircraft. This position was accessed by climbing up a light wooden- or rope ladder inside a tube running up inside the envelope. Some C-Class commanders fitted additional Lewis guns to the bottom of the gondola to provide added fire-power against submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

s. Firing these required the crew to lean out of the their cockpits or even stand on the landing skid to operate the weapon.

The main anti-submarine armament was bomb
A bomb is any of a range of explosive weapons that only rely on the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy...

s. Most patrols carried four 100 or 112-lb (45 or 50 kg) bombs, but these could be replaced with a pair of 230-lb (104 kg) bombs or depth charge
Depth charge
A depth charge is an anti-submarine warfare weapon intended to destroy or cripple a target submarine by the shock of exploding near it. Most use explosives and a fuze set to go off at a preselected depth in the ocean. Depth charges can be dropped by either surface ships, patrol aircraft, or from...

s. The standard British Lee-Enfield rifle
The Lee-Enfield bolt-action, magazine-fed, repeating rifle was the main firearm used by the military forces of the British Empire and Commonwealth during the first half of the 20th century...

 was often carried by one of the crew to destroy any mines
Naval mine
A naval mine is a self-contained explosive device placed in water to destroy surface ships or submarines. Unlike depth charges, mines are deposited and left to wait until they are triggered by the approach of, or contact with, an enemy vessel...

 found. A plate camera
Photographic plate
Photographic plates preceded photographic film as a means of photography. A light-sensitive emulsion of silver salts was applied to a glass plate. This form of photographic material largely faded from the consumer market in the early years of the 20th century, as more convenient and less fragile...

 could be carried, usually used for surveys to prepare nautical chart
Nautical chart
A nautical chart is a graphic representation of a maritime area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land , natural features of the seabed, details of the coastline, navigational hazards, locations of natural and man-made aids...


The standard crew was five – a pilot, a coxswain
The coxswain is the person in charge of a boat, particularly its navigation and steering. The etymology of the word gives us a literal meaning of "boat servant" since it comes from cox, a coxboat or other small vessel kept aboard a ship, and swain, which can be rendered as boy, in authority. ...

, an observer, a radio operator and a mechanic.


The design of the C-Class was unsophisticated. The type was unstable, with poor control authority. 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. It had a top speed of around 40 knots (75 km/h), making it vulnerable to enemy aircraft and even surface ships. Even at these modest speeds, and despite its strengthening ribs, the nose of the airship was prone to denting, further compromising handling.

The engines were prone to failure, regardless of the type used. This was mainly due to the extended duration of the patrols, which could reach 20 hours in length. The engines were run at virtually full speed all this time, leading to many units simply wearing out, and RNAS station maintenance crews became skilled at rapidly overhauling the engines. Other problems stemmed from the engine's magneto
A magneto is a type of electrical generator.Magneto may also refer to:* Magneto , permanent magnetic alternating current rotary generator* ignition magneto, magnetos on internal combustion engines...

s. Before the war, the majority of magnetos used worldwide had been made in Germany, usually by Bosch
Robert Bosch GmbH
Robert Bosch GmbH is a multinational engineering and electronics company headquartered in Gerlingen, near Stuttgart, Germany. It is the world's largest supplier of automotive components...

 and AEG
Allgemeine Elektricitäts-Gesellschaft was a German producer of electrical equipment founded in 1883 by Emil Rathenau....

; but the British-made Lucas
Lucas Industries plc
Lucas Industries plc was a famous British manufacturer of components for the motor industry and aerospace industry. It was based in Birmingham. It was listed on the London Stock Exchange and was once a constituent of the FTSE 100 Index...

 replacements were of poorer quality and it was common for crews to carry several spares on patrol and many became adept at changing them in mid-flight.

The open, unheated cockpits of the Coastals were uncomfortable; some crew members resorted to walking around the outside of the gondola on the grab-handles to stretch their legs. In winter crews were at risk from frostbite
Frostbite is the medical condition where localized damage is caused to skin and other tissues due to extreme cold. Frostbite is most likely to happen in body parts farthest from the heart and those with large exposed areas...

 and hypothermia
Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as . Body temperature is usually maintained near a constant level of through biologic homeostasis or thermoregulation...

. Often ground staff had to lift crewmen from their cockpit, they being unable to help themselves.

Shortly after entering service, the ballonet air-scoop was relocated from behind the front propeller to behind the rear propeller. This not only improved the efficiency of the system, but greatly improved the visibility from the front cockpits, making the difficult task of landing the airships slightly easier.

Despite these flaws, the C-Class was the only aircraft available that could mount the long patrols needed to keep the Western Approaches and carry a useful bomb load in the hope of destroying a U-Boat.


To maximise the amount of daylight for patrols, takeoffs would be made before dawn and landings would take place in darkness at night. RNAS stations were not equipped with floodlight
High-intensity discharge lamp
High-intensity discharge lamps are a type of electrical lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. This tube is filled with both gas and metal salts. The gas facilitates the...

s or marker lights, and most landings were made in near-total darkness, with only hurricane lanterns held by the ground crew providing basic illumination. Later C-Class airships had a hatch in the floor of the gondola to allow a flare
Flare (pyrotechnic)
A flare, also sometimes called a fusee, is a type of pyrotechnic that produces a brilliant light or intense heat without an explosion. Flares are used for signalling, illumination, or defensive countermeasures in civilian and military applications...

 to be fired downwards to light up the landing ground.

The RNAS provided a standard ration pack for each crew member for the flight. This was usually little more than some salted bacon or a sandwich, some Cadbury's chocolate and a flask of tea.

The airships carried no mechanical method of detecting submarines. On war patrols, crews had to rely on their own eyesight to find a U-Boat, but in 1918 experiments were carried out to develop a buoy
A buoy is a floating device that can have many different purposes. It can be anchored or allowed to drift. The word, of Old French or Middle Dutch origin, is now most commonly in UK English, although some orthoepists have traditionally prescribed the pronunciation...

 carrying a basic ASDIC set that would be trailed below the craft; however, the war ended before this project was completed.

If the sea was calm, it was sometimes possible to make out the wake of a submerged submarine's periscope
A periscope is an instrument for observation from a concealed position. In its simplest form it consists of a tube with mirrors at each end set parallel to each other at a 45-degree angle....

 poking above the surface, or even the faint outline of the submarine itself it was running just below the surface. The more reliable method was to search for a light oil slick on the surface coming from the various external bearings
Bearing (mechanical)
A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can...

 on the submarine. The airship crew would follow this trail until they reached the end of the slick, where it could be assumed the U-Boat was.

Most encounters started with the submarine on the surface. Even if the airship crew sighted the submarine, the enemy crew were just as likely to sight the slowly-approaching airship, dive and so have a good chance of escape.

When airships escorted convoys, it was more effective to shadow the convoy and wait for the submarine to attack. The release of air when a torpedo
The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...

 was fired and the weapon's wake would betray the submarine's position.

The overall offensive capabilities of the C-Class was weak – in total, only six U-Boats were confirmed sunk by the 35-strong class during World War I. However, they had a great deterrent value. The type allowed the RNAS to operate a continuous air presence in the Western Approaches and English Channel. U-Boat commanders were wary of the British airships and many chose to operate only outside the main shipping lanes, which greatly decreased the risk to convoys. Throughout 1918 not a single convoy ship was lost to U-Boat action whilst the convoy was being protected by an RNAS airship. The C-Class, and other RNAS airship classes, also contributed to the sinking of several U-Boats by surface ships, being able to track a submarine's course and guide a destroyer
In naval terminology, a destroyer is a fast and maneuverable yet long-endurance warship intended to escort larger vessels in a fleet, convoy or battle group and defend them against smaller, powerful, short-range attackers. Destroyers, originally called torpedo-boat destroyers in 1892, evolved from...

 or armed trawler
Naval trawler
A naval trawler is a vessel built along the lines of a fishing trawler but fitted out for naval purposes. Naval trawlers were widely used during the First and Second world wars. Fishing trawlers were particularly suited for many naval requirements because they were robust boats designed to work...

 to its position. Even if the airships attacked a target but failed to damage it, the submarine would often abort an attack once the commander knew an airship was on hand. Similarly, airship crews soon realised that after an attack a submarine commander would often surface to confirm his "kill", and to allow his boat to exit the area at maximum speed. Airships simply had to hover over the site of the attack and wait for the U-Boat to come to the surface.

The sluggish performance of the Coastal class made them vulnerable to enemy aircraft. The RNAS was careful to keep its airships away from the central and eastern parts of the English Channel, which were in range of German bombers and some fighters. On the rare aerial encounters that occurred, the airship crew's tactic was to run for the nearest coast, where anti-aircraft guns
Anti-aircraft warfare
NATO defines air defence as "all measures designed to nullify or reduce the effectiveness of hostile air action." They include ground and air based weapon systems, associated sensor systems, command and control arrangements and passive measures. It may be to protect naval, ground and air forces...

 could drive away the attackers. It was difficult to physically destroy the blimps – bullets could knock out the engines, which would simply cause the airship to drift; or puncture the envelope, which would cause the craft to slowly settle to the ground. German fighter aircraft
Fighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...

 posed the greatest threat as their tracer ammunition
Tracer ammunition
Tracer ammunition are bullets that are built with a small pyrotechnic charge in their base. Ignited by the burning powder, the phosphorus tail burns very brightly, making the projectile visible to the naked eye...

 could ignite the hydrogen in the envelope. The gunner manning the gun position at the top of the envelope was especially vulnerable, being directly in an attacker's line of fire and sitting atop a large, slow-moving bag of hydrogen. Many airship crews decided that the upper gun was ineffective, and moved it down onto the gondola to provide further offensive power.

Towards the end of 1917, many of these ships were in need of a complete refit having been in commission for over two years. Initially several were put in order, but it was later decided instead to replace each ship as it became no longer fit to fly by the more modern Coastal type known as the C-Star
C-Star class blimp
-References:* London, P. U-Boat Hunters: Cornwall's Air War 1916-19 Dyllansow Truran, Truro. ISBN 1-85022-136-9-External links:*...

 (C*) -class. These had a larger envelope with a capacity of 210000 cu ft (5,946.5 m³) containing six ballonets of 68860 cu ft (1,949.9 m³) in total for an increased useful lift of 4030 lb (1,828 kg); had a greater fuel capacity, a top speed of 57 mph (91.7 km/h), and had a service ceiling
Service ceiling
With respect to aircraft, a ceiling is the maximum density altitude an aircraft can reach under a set of conditions.The word ceiling can also refer to the height of the lowest obscuring cloud layer above the ground.-Service ceiling:...

 of 9500 ft (2,895.6 m).

The most successful Coastal airship (often described as "the darling of the airship service" during the War) was C-9, operating out of RNAS Mullion
Mullion, Cornwall
Mullion is a civil parish and village in Cornwall, United Kingdom. It is situated on the Lizard Peninsula approximately five miles south of Helston....

 in Cornwall
Cornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...

. C-9 had one confirmed and three probable "kills" during its long career. She entered service in June 1916 and was struck off on 14 September 1918, after completing 3,720 hours of flying, covering 68200 miles (109,757 km). It was claimed that in her 805 days of service she had never missed an assigned patrol.

In July 1917 C-24 set a new world record for airborne endurance when she mounted a patrol that lasted for 24 hours, 15 minutes.

A total of 45 standard Coastals and C-Stars were built. Twelve were totally destroyed in one way or another, but only two were lost to enemy action in the entire war, and just four survived to the Armistice.

Specifications (typical)

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