The blimps were used for long anti-submarine patrols in the Western Approaches and English Channel, protecting convoys from German U-boats.

10 Astra-Torres airship designed by the Spanish engineer Leonardo Torres Quevedo,[2][3][4] 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.

[5][6] Sometimes referred to as the "ugliest" dirigibles ever made,[6] production Coastals looked very similar, but used a bespoke gondola with canvas sides built over a wooden frame.

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.

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.

Some C-Class commanders fitted additional Lewis guns to the bottom of the gondola to provide added firepower against submarines.

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.

[10] 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.

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.

RNAS stations were not equipped with floodlights or marker lights, and most landings were made in near-total darkness, with only hurricane lanterns held by the ground crew providing basic illumination.

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.

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.

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.

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.

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.

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.