{{Short description|1964 hovercraft model by Saunders-Roe}} {{refimprove|date=August 2018}} {{Use dmy dates|date=November 2016}} {{Use British English|date=November 2016}} {{Infobox ship |section1={{Infobox ship/image |image=PACV cruising full speed.jpg |image_caption=US Navy PACV (SK-5) in Vietnam }}
|section2={{Infobox ship/class overview |name=SR.N5 ''Warden'' class |builders=British Hovercraft Corporation |operators= |class_before=SR.N3 |class_after= |subclasses= |cost= |built_range=1964-1968<ref name="Porter">{{cite web |last1=Porter |first1=Mark |title=The SR.N5 and SR.N6 Hovercraft |url=http://www.btinternet.com/~mark.e.porter/history/srn6.html |website=Hovercraft Histories |access-date=14 April 2026 |archive-url=https://web.archive.org/web/20050316165943/http://www.btinternet.com/~mark.e.porter/history/srn6.html |archive-date=16 March 2005}}</ref> |in_service_range= |in_commission_range= |total_ships_building= |total_ships_planned= |total_ships_completed=14<ref name="Porter" /> |total_ships_canceled= |total_ships_active= |total_ships_laid_up= |total_ships_lost= |total_ships_retired= |total_ships_scrapped= |total_ships_preserved= }}
|section3={{Infobox ship/characteristics |hide_header= |header_caption= |class= |type=Hovercraft |tonnage= |displacement={{convert|17500|lb|t|abbr=on}} maximum |length={{convert|39|ft|5|in|m|abbr=on}} |beam={{convert|22|ft|9|in|m|abbr=on}} |height={{cvt|16|ft|9|in|m}} (skirt inflated) |draught= |power= |propulsion=1 × {{convert|900|shp|0|abbr=on}} Rolls-Royce Gnome turbine engine for lift and propulsion |speed={{convert|70|kn|lk=in}}{{efn|with 6 inch clearance under skirt}} |range={{cvt|240|nmi|km}} (3 hr 30 min) at {{cvt|15,800|lb|kg}} weight |capacity={{cvt|6,600|lb|kg}} load including crew and fuel |troops=16 |complement= |crew= |time_to_activate= |sensors= |EW= |notes=from ''Flight''<ref name = "flight 65 10">''Flight'' 23 July 1965, p. 10.</ref> }} }} The Saunders-Roe '''SR.N5''' (or ''Warden'' class) was a medium-sized hovercraft which first flew in 1964. It has the distinction of being the first production-built hovercraft in the world.<ref>{{cite book |title=A Dictionary of Aviation |first=David W. |last=Wragg |isbn=9780850451634 |edition=first |publisher=Osprey |year=1973 |page=250}}</ref>
A total of 14 SR.N5s were constructed. While Saunders-Roe had developed and produced the type, an additional seven vehicles were also manufactured by Bell Aerosystems under licence in the United States, designated as the '''Bell SK-5'''. A number of SK-5s were operated by the US military, this includes a number which became Patrol Air Cushion Vehicles (PACV), and saw action during the Vietnam War. The SR.N5 was subsequently developed into a "stretched" variant, which was designated as the SR.N6; this model had a much expanded payload capacity and went on to be produced in greater numbers than the SR.N5.
==Development== During the late 1950s and early 1960s, British inventor Sir Christopher Cockerell had, in cooperation with British aircraft manufacturer Saunders-Roe, developed a pioneering new form of transportation, in the form of the experimental SR.N1 vehicle, which became widely known as the hovercraft.<ref name = "pay sym 72">Paine and Syms 2012, p. 82.</ref> By 1964, Saunders-Roe had commenced design work on multiple hovercraft designs; in addition to the relatively huge SR.N4 and studies into a prospective 2,000 ton freighter, there was also interest in developing smaller hovercraft as well.<ref name = "pay sym 147">Paine and Syms 2012, p. 147.</ref>
In 1963, American manufacturer Bell Aerosystems successfully negotiated for the exclusive rights to market the SR.N5 in the North American market, as well as a licence to locally produce the type from Westland Aircraft, the parent company of Saunders-Roe.<ref name = "prender 1801">Prenderghast 2015, pp. 180-181.</ref> In North America, the type was marketed under the designation of ''Bell SK-5''. Seven SR.N5s were directly sold to Bell; the type was militarised into the Patrol Air Cushion Vehicle (PACV) and adopted by the US military.<ref name = "prender 181">Prenderghast 2015, p. 181.</ref> Japanese conglomerate Mitsubishi also secured its own license to independently build the SR.N5.<ref name = "Amyot 22"/>
Construction of the first SR.N5 occurred during 1963; it performed its first flight on 11 April 1964.<ref name = "Amyot 22">Amyot 2013, p. 22.</ref> That same month, the first SR.N5 commenced sea trials; as a result of experiences gathered from these early test runs, various changes were made to the design. Specifically, the fin area was increased while a new system for ducting plenum thrust was also adopted, which improved the craft's low speed handling.{{CN|date=February 2020}}
In response to customer feedback, which showed interest in a stretched variant of the SR.N5 that would be capable of carrying a much greater payload, Saunders-Roe quickly commenced work on such a project. According to the company's own projections, an increase of the SR.N5's payload by 110 per cent would only reduce performance by 10 per cent as the increased payload was in part offset by the expanded cushion area, which meant that cushion pressure would not need to be substantially increased instead.<ref name = "pay sym 147"/> To validate and demonstrate the concept, the ninth SR.N5 to have been produced was remanufactured into such a configuration, the first of the type to be lengthened in this manner. This stretched variant was subsequently designated SR.N6 and put into production.<ref name = "pay sym 147"/>
==Design== thumb|Crew and officials gathered in front of an SR.N5 in the livery of SFO Airlines The SR.N5 is an early production hovercraft that was primarily designed for passenger service.<ref name = "pay sym 147 238">Paine and Syms 2012, pp. 147, 238.</ref> In a typical civilian configuration, the SR.N5 possessed a gross weight of seven tonnes and could carry up to 20 passengers.<ref name = "Amyot 22"/>
It was piloted from a forward-seated position at the front of the main passenger cabin.<ref name = "pay sym 148">Paine and Syms 2012, p. 148.</ref> The pilot would exercise control over the direction of the craft via a series of control surfaces that was located immediately behind the variable pitch propeller. Early on, pilots were normally aviators who had been recruited from the Royal Air Force and Fleet Air Arm, however it has been claimed that experienced mariners would often be more skilled at operating the type, if not taking more time to adapt to its atypical form of propulsion, in part due to their familiarity at safely navigating within uncontrolled maritime environments.<ref name = "pay sym 180 182">Paine and Syms 2012, pp. 180-182.</ref> Around 20 per cent of the operating costs of the type have been attributed to maintenance of the 4 ft flexible skirt, which reportedly lasted for up to 500 hours, while similar cost levels have been reported for fuel.<ref name = "pay sym 181">Paine and Syms 2012, p. 181.</ref>
The SR.N5 featured an improved skirt design over preceding hovercraft, featuring ''fingers'' and forward puff ports; these changes resulted in improved forward control and reduced skirt wear; fingers had not been present upon the initial version of the skirt used prior to 1966.<ref name = "pay sym 134 176 177">Paine and Syms 2012, pp. 134, 176-177.</ref><ref name = "Amyot 96">Amyot 2013, p. 96.</ref> The endurance of the fingers would be progressively improved over time, issues with salt spray negatively affecting both the engine and propeller were also encountered early on. An initial experience of some components having short overhaul lifespans or being unreliable was encountered during early days.<ref name = "pay sym 221 223">Paine and Syms 2012, pp. 221-223.</ref> During the early years of not only the SR.N6 but other hovercraft as well, the hovercraft skirt remained an unresolved area of difficulty during this era.<ref name = "pay sym 166">Paine and Syms 2012, p. 166.</ref>
The SR.N5 was powered by a single marinised model of the Bristol Gnome turboshaft engine; this drove both a single rear-facing 9 ft (2.74 m) diameter 4-bladed Dowty Rotol variable-pitch propeller along with a 7 ft (2.13 m) diameter centrifugal lift fan.<ref name = "pay sym 148"/> The Gnome engine was an expensive component for operators, leading to some establishing their own internal overhaul facilities and making arrangements with other Gnome operators, including the Royal Navy, to reduce costs from relying on costly services from Rolls-Royce Limited.<ref name = "pay sym 148 180 181">Paine and Syms 2012, pp. 148, 180-181.</ref> American SK-5s were rebuilt to use the General Electric 7LM100-PJ102 gas turbine engine in place of the Gnome powerplant.<ref name=Armor13>{{harvnb|Keaveney|1993|pp=13}}</ref><ref name = "prender 17980">Prenderghast 2015, pp. 179-180.</ref>
The Saunders-Roe SR.N6 (also known as the ''Winchester'' class) was based on the SR.N5 design to carry 110% more payload, making it more economical to run passenger services.
==Operational history== ===Civilian service=== thumb|SK-5 ''City of Oakland'' operated by SFO Airlines The SR.N5 was the world's first commercially successful hovercraft; it was placed onto various routes around the world.<ref name = "Amyot 22"/>
At least two of the Bell-built SK-5s were placed into civilian service.<ref>[http://www.flightglobal.com/pdfarchive/view/1965/1965%20-%203198.html "Air-Cushion Vehicle International Supplement."] ''Flight International'', 30 December 1965. p. 77.</ref> San Francisco and Oakland Helicopter Airlines (SFO Airlines) operated the SK-5 for scheduled passenger services in the San Francisco Bay Area during the mid 1960s as a supplement to its helicopter airline service. According to a report compiled by the U.S. Department of Transportation, the Bay Area service, which was operated on a trial basis, had proved popular with the travelling public while the SK-5 itself was found to be well-suited to over-water routes; its operations were negatively impacted by high operating costs and reliability issues, as well as by regulations that prevented a variable fare structure being adopted.<ref>{{cite book |url = https://books.google.com/books?id=RB1JAQAAIAAJ |title = Directory of Research, Development & Demonstration Projects |publisher = U.S. Department of Transportation |date = January 1970 |page = 8}}</ref><ref>{{cite web |url = https://www.mercurynews.com/2019/01/31/hovercraft-on-the-san-francisco-advocates-say-its-time-has-come/ |title = Hovercraft on the San Francisco Bay? Advocates say its time has come |publisher = The Mercury News |date = 31 January 2019 |first = Erin |last = Baldassari}}</ref>
===Military service=== {{See|Patrol Air Cushion Vehicle}} A total of four SR.N5s entered service with the Interservice Hovercraft Trials Unit at RNAS Lee-on-Solent (HMS Daedalus) for trials and operational missions. Assigned the military aircraft registration numbers XT492, XT493, XT657, and XW246, these were deployed in the United Kingdom, Malaysia, Thailand, Aden, Libya, and Belgium. Two were subsequently converted to SR.N6s.<ref>{{Cite web|url=https://www.hovercraft-museum.org/collections/|title=The Collection|website=Hovercraft-Museum.org|publisher=Hovercraft Museum|access-date=1 February 2020|archive-date=7 October 2024|archive-url=https://web.archive.org/web/20241007195110/https://www.hovercraft-museum.org/collections/|url-status=dead}}</ref> XT492 is prominently featured in the final episode of the 1971 ''Doctor Who'' serial ''The Sea Devils''.{{Citation needed|date=February 2020}}
Three Bell SK-5s saw service with the United States Navy, while another three with the United States Army; the type participated in the Vietnam War during the late 1960s. Following the conflict, the United States Coast Guard also operated multiple second-hand SK-5s on a trial basis.<ref>{{Cite web|url=https://cgaviationhistory.org/1970-evaluation-of-hovercraft-suitability-for-coast-guard-use-conducted/|title=1970 – in-depth evaluation of hovercraft suitability for Coast Guard use conducted|website=CGAviationHistory.org|publisher=Coast Guard Aviation Association|access-date=1 February 2020}}</ref>
The Boat Company of the Royal Brunei Malay Regiment (forerunner of the Royal Brunei Navy)<ref>{{Cite web|title=Royal Brunei Navy history|url=https://navy.mindef.gov.bn/Site%20Pages/History.aspx|website=Navy.MinDef.gov.bn|location=Royal Brunei Navy Headquarters, Muara Naval Base|publisher=Defence Information Technology Unit, Ministry of Defence, Brunei Darussalam|date=n.d.|access-date=6 January 2024|url-status=live|archive-url=https://web.archive.org/web/20181023223656/http://www.RBN.MinDef.gov.bn/Site%20Pages/History.aspx|archive-date=23 October 2018}}</ref><ref>{{Cite web|url=https://navy.mindef.gov.bn/Site%20Pages/2nd%20Commander.aspx|title=2nd Commander – YDM Pehin Datu Juragan Laila Diraja Dato Seri Pahlawan Colonel (B) Haji Kefli bin OKLS Haji Razali|website=Navy.MinDef.gov.bn|location=Royal Brunei Navy Headquarters, Muara Naval Base|publisher=Defence Information Technology Unit, Ministry of Defence, Brunei Darussalam|date=n.d.|access-date=7 January 2024}}</ref> and the Canadian Coast Guard each had one SR.N5.{{Citation needed|date=February 2020}}
==Preservation== By 2013, only a single SR.N5 was reportedly still intact; having been primarily used as an overseas demonstrator, it had been withdrawn during the 1980s and preserved at the Hovercraft Museum at Lee-on-the-Solent.<ref>{{cite web |url = https://www.imeche.org/news/news-article/SR.N5_Hovercraft_receives_top_engineering_honour |title = Hampshire's SR.N5 Hovercraft receives top engineering honour |publisher = Institution of Mechanical Engineers |date = 16 September 2013}}</ref>
==Notes== {{notelist}} ==References== ===Citations=== {{Reflist}} ===Bibliography=== {{refbegin}} *{{citation |editor-last= Amyot |editor-first=J.R. |title=Hovercraft Technology, Economics and Applications |series=Studies in Mechanical Engineering II|publisher= Elsevier |date=1989 |isbn=1-4832-9085-9}} *{{Cite magazine|url=https://www.flightglobal.com/pdfarchive/view/1964/1964%20-%203178.html |title=Westland SR.N5 |magazine=Air Cushion Vehicles (Flight International supplement) |date=23 July 1964 |pages=5–11 |archive-date=2017-02-20 |archive-url=https://web.archive.org/web/20170220093646/https://www.flightglobal.com/pdfarchive/view/1964/1964%20-%203178.html }} * [https://web.archive.org/web/20091002075732/http://www.hovercraft-museum.org/mussrn5.html "SR.N5."] ''Hovercraft Museum''. * [https://web.archive.org/web/20091001220026/http://www.hovercraft-museum.org/craft.html "Craft Built."] ''Hovercraft Museum''. * {{cite magazine |last=Keaveney |first=Kevin |date=July–August 1993 |title=Cavalry Afloat: The 39th Cavalry Platoon in the Mekong Delta |url=https://www.dvidshub.net/publication/issues/33913 |magazine=Armor |location=Fort Knox |publisher=US Army Armor Center |access-date=6 August 2018 |issn=0004-2420 }} *{{cite book|last1=Paine |first1=Robin |first2= Roger |last2=Syms |url=https://books.google.com/books?id=hXuAevQ3SS0C |title=On a Cushion of Air |publisher=Robin Paine/Roger Syms/Writersworld |date= 2012 |isbn=978-0-95689-780-0 |via=Google Books}}. * Prenderghast, Gerald. ''Britain and the Wars in Vietnam.'' McFarland, North Carolina 2015. {{ISBN|0-7864-9924-9}}. {{refend}}
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{{DEFAULTSORT:Sr.N5}} Category:Military hovercraft Category:Saunders-Roe Category:Vehicles introduced in 1964