The British NS (North Sea) class non-rigid airships were the largest and last in a succession of "blimps" that served with the Royal Naval Air Service during World War I; developed from experiences gained with earlier classes to operate off the east coast of Britain on long-range patrols. Despite early problems, examples of the class went on to break all flying records for non-rigid airships, and the type became regarded as the most efficient of its kind.
Design
The NS class airship was developed in response to the increasing requirement of the RNAS to carry out long-range anti-submarine patrols and convoy escort duties off the west coast of Great Britain, though its name came from the fact that the type was intended to work in collaboration with the Grand Fleet which mainly operated in the North Sea east of the British Isles.
In 1916, Britain's rigid airship programme was unable to provide an effective airship; the NS class was developed as a substitute using experiences gained with the Coastal and improved C* classes to create a larger and more weather-worthy long-endurance non-rigid vessel. The main requirements for the new design were: Capability to carry out flights of considerable duration [ 24 hours with a speed of ]. Great reliability. The necessary lift to carry an ample supply of fuel. Adequate arrangements to accommodate a double crew in comfort.
Approval was given in January 1916 for the construction of six NS class airships; designed and built at RNAS Kingsnorth on the Hoo Peninsula, not far from the Chatham Dockyard in Kent.
Envelope
Similar to the Coastal and C-Star classes, the "North Seas" employed a tri-lobe envelope based on the Astra-Torres design principles. It incorporated all the improvements that had been previously suggested for those classes – its shape was streamlined throughout, and having a capacity of it was significantly larger than that of the "Coastals". Six ballonets of in total were provided; equivalent to 35.5% of the total volume.
Attached to the envelope were four fins. The smaller top fin was merely for stabilizing purposes; while the larger other three were identical in size and shape, and carried the rudder and elevators. The aluminium fuel tanks were initially situated above the top ridges of the envelope, but its varying shape caused the aluminium fuel lines to fracture and consequently the tanks were later placed inside the envelope.
Cars
The first examples of the type were equipped with two enclosed cars slung from the underside of the envelope – a control car, and to the rear an engineers' car (power or engine car), joined by an exposed wooden walk-way suspended on cables.
The control car was rectangular in cross-section, long and high, and was constructed from a frame of light steel tubing braced with diagonal wires. The forward portion was clad in duralumin, and the remainder covered with fabric laced to the framework. Duralumin sheeting was chosen instead of aluminium as it is not affected by the combined action of sea air and water. Windows and portholes provided both light for the crew, and afforded a good field of view.
The forward section of the control car was extensively glazed, and formed the pilot's cabin which housed all the flight controls, navigating instruments, engine telegraphs and voice pipes. Behind this was the wireless telegraphy cabin, while the living and sleeping accommodation for the 10-man crew was located at the rear of the car. In addition to the radio equipment, the wireless operators' compartment carried Aldis lamps as well as international maritime signal flags. The latter could be lowered from the control car, and were effective for communicating with foreign vessels.
The engineers' car housed the controls for the engines, and gave access to a flanged hotplate for cooking that was attached to one of the engine exhaust pipes. Two dynamos and batteries provided power for the ship's electrical systems which included lights, telephones and signalling lamps etc.
Propulsion
The type was initially fitted with a pair of Rolls-Royce Eagle engines mounted one either side of the power car in streamlined enclosures. Each drove a diameter four-bladed propeller on independent shafts through an elaborate transmission system.
Armament
A maximum of six bombs could be carried as well as up to five machine-guns. Similar to the Coastal and C-Star class airships, one gun was mounted on a platform on top of the envelope which was reached through a climbing shaft.