Editing SR.N4 (section)

==Development==
===Origins===
In August 1962, the original concept for the SR.N4, which had been conceived at the same time as the [[SR.N2]] was being designed, was abandoned.{{sfn|Paine|Syms|2012|pp=131,236}} This original concept had effectively been a pair of elongated SR.N2 fixed together in a side-by-side placement and would have been powered by an arrangement of four pairs of [[Bristol Siddeley Nimbus|Blackburn A.129]] [[turboshaft]] engines. In its place, a new proposed hovercraft, which was referred to as the SR.N4 as well, was considerably larger and heavier, and powered by three pairs of [[Bristol Proteus|Rolls-Royce Proteus]] [[Marinisation|marinised]] [[gas turbine]] engine.{{sfn|Paine|Syms|2012|p=131}} However, during early 1963, work on the SR.N4 was put on hold due to a greater priority having been placed on the completion of the [[SR.N5]] instead. In late 1964, it was decided to recommence design work on the proposed SR.N4.{{sfn|Paine|Syms|2012|pp=131, 147}}

By the end of 1964, it had been concluded that, due to the improved projected performance of the craft's flexible skirt having lowered the power requirements involved, only two pairs of Proteus engines would be required instead of three.{{sfn|Paine|Syms|2012|p=238}} At this stage, the proposed design for the SR.N4 had a displacement of 165 tons and a payload of up to 33 cars and 116 passengers; this would not substantially differ from the final design adopted for the type.{{sfn|Paine|Syms|2012|p=238}}

Experience gained from the SR.N5 and [[SR.N6]] would contribute to the design of aspects of the larger SR.N4, which would be four times the size of any preceding hovercraft.{{sfn|Paine|Syms|2012|p=167–168}}{{sfn|Paine|Syms|2012|p=202}} This approach is credited with having been less expensive and having resulted in a more commercially viable hovercraft than would have been if it had been constructed as per the earlier incarnation of the SR.N4 and then required to perform modifications to improve the capabilities of aspects such as the skirt, which had been considerably advanced by development of the SR.N5 and SR.N6.{{sfn|Paine|Syms|2012|p=236}} Specific improvements included the adoption of triangular rubber 'finger'-like attachments to the curtain which provided for a better seal between the hovercraft and the water's surface as well as being cheaper and easier to maintain than previous configurations.{{sfn|Paine|Syms|2012|p=236–238}}

During the mid-1960s, some management figures within [[British Rail]] had become interested in the potential for operating a fleet of hovercraft for scheduled services that would link up to Britain's national rail system.{{sfn|Paine|Syms|2012|p=201–202}} In November 1965, [[Frank Cousins (British politician)|Frank Cousins]], the [[Minister of Technology]], announced that British Rail would participate in the development of the SR.N4 and would be a customer for the type. While orders had already been placed for the SR.N4 by this point, the [[British Railways Board]] had decided to commit to taking delivery of the first craft to be produced; this was particularly convenient as the two orders which had been placed by Swedish operator [[Hoverlloyd|Cross-Channel Hover Services]] specifically excluded accepting delivery of the first example.{{sfn|Paine|Syms|2012|p=202–203}} By the end of 1965, having acquired three firm orders, it was now plausible for production of the SR.N4 to proceed.{{sfn|Paine|Syms|2012|p=203}}

===Prototype and testing===
Having realised that the market for large hovercraft was not yet large enough to sustain a number of competing companies at that time, in 1966, the hovercraft divisions of both [[Saunders-Roe]] and [[Vickers Supermarine]] merged to form a new united entity, known as the [[British Hovercraft Corporation]] (BHC), which was headquartered on the [[Isle of Wight]].{{sfn|Paine|Syms|2012|p=165–166}} In autumn 1966, production work commenced on the structure of the first SR.N4, which was internally designated ''001''. The vehicle was assembled in the same hangar in which the three [[Saunders-Roe Princess]] [[flying boat]]s had been constructed 15 years before.{{sfn|Paine|Syms|2012|p=236}}{{sfn|Paine|Syms|2012|p=238}} During 1967, as 001 was taking shape, it was announced that the SR.N4 had been named the ''Mountbatten-class''.{{sfn|Paine|Syms|2012|p=238}} Throughout the development and production of 001, both Hoverlloyd and [[Seaspeed]] carefully monitored progress on the project.{{sfn|Paine|Syms|2012|p=295}}

In October 1967, the completed 001 was officially presented to gathered members of the press and to various representatives and dignitaries.{{sfn|Paine|Syms|2012|p=249}} On 20 November 1967, the first engine run was performed, after which 11 weeks of intense test runs on land were performed and the exposed faults were addressed. On 4 February 1968, 001 was launched onto water for the first time.{{sfn|Paine|Syms|2012|p=249}}{{sfn|Paine|Syms|2012|p=297}} The launch, while successful, had involved some risk due to the lack of space to manoeuvre with an untested control system. Later that same day, 001 conducted its [[maiden flight]].{{sfn|Paine|Syms|2012|p=249}}{{sfn|Paine|Syms|2012|p=297–300}}

As experience with the prototype accumulated, the control arrangement proved to be quite effective even within confined spaces; incidents involving a loss of control did occur during the test programme, but these were mainly due to error on the part of the operator.{{sfn|Paine|Syms|2012|p=303–305}} Ray Wheeler, BHC's chief engineer, was reportedly very pleased with the progress made during the initial trials. At the same time, 001 required substantial refinement and alteration in order to become a commercially viable craft.{{sfn|Paine|Syms|2012|p=305}} The air intakes had to be substantially modified in order to minimise [[salt]] ingestion, and a revised skirt system was also developed.{{sfn|Paine|Syms|2012|p=305}}