Coastal - class blimp The Coastal Class ( often known as the C - Class or simply the ' Coastals ' ) were a class of blimp used by the Royal Naval Air Service ( RNAS ) during World War I . The C class blimp operated by the United States Navy after the war was a completely unrelated design . In total 35 Coastals were built , all at RNAS Kingsnorth , Kent . 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 , while others were replaced by the improved C - Star class as they became unfit for service . The blimps were used for long anti - submarine patrols in the Western Approaches and English Channel , protecting convoys from German U - Boat 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 from the No . 10 Astra - Torres airship , and a gondola built using the front - sections of two Avro seaplane fuselages joined together back - to - back to provide one tractor - and one pusher propeller . 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 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 sheet reinforced with bamboo 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 configuration and carried the elevators , while the single vertical fin below the envelope incorporated a rudder . 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 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 ( 111 kW ) each . Some replaced the aft unit with a Renault engine of 220 hp ( 164 kW ) , and various airships were deployed with a 100 hp ( 74 kW ) 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 . 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 Lewis guns . These could be mounted in a variety of places around the gondola . Another Lewis Gun was mounted on a Scarff ring 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 firepower against submarine 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 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 s . The standard British Lee - Enfield rifle was often carried by one of the crew to destroy any mines found . A plate camera could be carried , usually used for surveys to prepare nautical chart s . The standard crew was five – a pilot , a coxswain , an observer , a radio operator and a mechanic . Performance . 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 magnetos . Before the war , the majority of magnetos used worldwide had been made in Germany , usually by Bosch and AEG ; but the British - made Lucas 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 and hypothermia . 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 . Operations . 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 s or marker lights , and most landings were made in near - total darkness , with only hurricane lantern s 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 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 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 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 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 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 or armed trawler 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 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 posed the greatest threat as their tracer ammunition 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 * ) - class . These had a larger envelope with a capacity of containing six ballonets of in total for an increased useful lift of ; had a greater fuel capacity , a top speed of , and had a service ceiling of . 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 in Cornwall . " 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 . 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 .