Editing Short Stirling (section)

==Development==
[[File:Short Stirling - Royal Air Force Transport Command, 1943-1945. CH16483.jpg|thumb|Interior of Short Stirling Mark V of Transport Command fitted with seating, 1944]]

===Origins===
In the 1930s, the Royal Air Force (RAF) was interested primarily in twin-engined [[bombers]].<ref name = "norris 3"/> These designs put limited demands on engine production and maintenance, both of which were already stretched with the introduction of so many new types into service. Power limitations were so serious that the British invested in the development of huge engines in the 2,000-[[horsepower]] (1,500&nbsp;kW) class to improve performance. During the late 1930s, none of these were ready for production. The [[United States]] and the [[Soviet Union]] were pursuing the development of bombers powered by arrangements of four smaller engines; the results of these projects proved to possess favourable characteristics such as excellent range and fair lifting capacity, and in 1936, the RAF also decided to investigate the feasibility of the four-engined bomber.<ref name = "norris 3"/>

The Air Ministry published [[List Of Air Ministry Specifications|Specification B.12/36]], for a high-speed, long-range, four-engined [[strategic bomber]] aircraft that would be capable of being designed and constructed at speed.<ref name = "norris 3"/> The bomb load was to be a maximum of {{convert|14,000|lb|kg}} carried to a range of {{convert|2,000|mi|km}} or a lesser payload of {{convert|8,000|lb|kg}} to {{convert|3,000|mi|km}} (very demanding for the era). It was to have a crew of six and was to have a normal all-up weight of 48,000&nbsp;lb, while a maximum overload weight of 65,000&nbsp;lb was also envisioned.<ref name = "norris 3"/> The aircraft would have to be capable of cruising at speeds of 230&nbsp;mph or greater while flying at {{convert|15000|ft|m|abbr=on}}, carrying three gun turrets (located in the nose, amidships, and rear positions) for defence.<ref name="ButtlerSecret">{{Harvnb|Buttler|2004|p=96}}</ref>

The aircraft should also be able to be used as a troop transport for 24 soldiers and be able to use catapult assistance for takeoff when heavily laden.<ref name="Barnes p371">{{Harvnb|Barnes|1967|p=371.}}</ref><ref name="ButtlerSecret"/> The concept was that the aircraft would fly troops to far corners of the [[British Empire]] and then support them with bombing. To help with this task, as well as ease production, it needed to be able to be broken down into parts, for transport by train.<ref name= "Flight p. 96">{{Harvnb|''Flight'' 29 January 1942|p=96}}</ref> Since it could be operating from limited "back country" airfields, it needed to lift off from a {{convert|500|ft|m|abbr=on}} runway and be able to clear {{convert|50|ft|m|abbr=on}} trees at the end, a specification with which most small aircraft would have a problem today. Aviation author Geoffrey Norris observed that the stringent requirements given in the specification for the prospective aircraft to be able to make use of existing infrastructure, specifically the specified maximum wingspan of 100 feet, adversely affected the Stirling's performance, such as its relatively low ceiling and its inability to carry anything larger than 500&nbsp;lb bombs.<ref name = "norris 3">{{harvnb|Norris|1966|p=3}}</ref>

In mid-1936, Specification B.12/36 was sent out to [[Supermarine]], [[Boulton Paul]], [[Handley Page]], and [[Armstrong Whitworth]]. In August, the specification was issued to the rest of British industry.<ref name = "ButtlerSecret"/> Left out of those asked to tender designs, Shorts were later included because the company already had similar designs in hand while possessing ample design staff and production facilities to fulfil production commitments. Shorts were producing several four-engined [[flying boat]] designs of the required size and created their S.29 proposal by removing the lower deck and boat hull of the [[Short Sunderland|S.25 Sunderland]]. The new S.29 design was similar to the Sunderland; the wings and controls were the same, construction was identical, and it even retained the slight upward bend at the rear of the fuselage, which had originally been intended to keep the Sunderland's tail clear of sea spray. As originally designed, the S.29 was considered to be capable of favourable high-altitude performance.<ref name = "norris 3"/>

Following a Tender Design Conference in October 1936, the S.29 was low down on the short list of designs considered. Vickers Type 293 submission was first followed by the Boulton Paul P.90, Armstrong Whitworth's AW.42, the Supermarine Type 316, and then the Short S.29. The Supermarine was ordered in prototype (two aircraft) form as the revised [[Supermarine Type 317]]{{refn|group=N|The Type 317 had increased wing area over the Type 316 and twin fins. Supermarine were told not to proceed further with their Merlin-engined alternative, the Type 318, to concentrate on the Type 317}} in January 1937. An alternative design to the Supermarine was needed for insurance, and Shorts should build it, as they had experience with four-engined aircraft. The original design had been criticised when considered, and in February 1937, the Air Ministry suggested modifications to the design, including considering the use of the [[Bristol Hercules]] radial engine as an alternative to the [[Napier Dagger]] inline, increasing service ceiling to 28,000&nbsp;ft (carrying a 2000&nbsp;lb of bombs) and reducing the wingspan.<ref>{{Harvnb|Buttler|2004|p=98}}</ref> Shorts accepted this large amount of redesign work. The project had added importance due to the death of Supermarine's designer, [[Reginald Mitchell]], which had generated doubt within the Air Ministry about the ability of Supermarine to deliver.<ref>{{Harvnb|Buttler|2004|p=99}}</ref> Two prototypes were ordered from Shorts.{{sfn|Buttler|2004|p=99}}

The S.29 used the Sunderland's {{convert|114|ft|m|abbr=on}} wing and it had to be reduced to less than {{convert|100|ft|m|abbr=on}}{{refn|The contemporary P.13/36 specification that led to the Handley Page Halifax and Avro Manchester was for twin-engined aircraft that were expected to be same weight as the [[Vickers Warwick|B.1/35 bomber specification]], which was also limited to 100 ft wingspan, but "a good deal smaller and faster".{{sfn|Buttler|2004|p=101}}|group=N}}<ref>{{Harvnb|Mondey|1994|p=189.}}</ref><ref>{{harvnb|Winchester|2005|p=48.}}</ref><ref name = "norris 3"/> To get the needed lift from a shorter span and excess weight, the redesigned wing was thickened and reshaped.<ref name = "norris 3"/> The wingspan was often said to be limited to 100&nbsp;ft so the aircraft would fit into existing hangars, but the maximum hangar opening was {{convert|112|ft|m|abbr=on}} and the specification required outdoor servicing.<ref name= "Flight p. 96"/> The wingspan limit was a method of stopping aircraft from being too large.<ref>{{Harvnb|Buttler|2004|p=100}}</ref> In June 1937, the S.29 was accepted as the second string for the Supermarine Type 317 and formally ordered in October; Shorts and Supermarine were issued with instructions to proceed.<ref name = "norris 3"/>

===Prototypes===
The Air Ministry issued Shorts with contract number 672299/37, under which a pair of prototype S.29s was ordered.<ref name = "norris 3"/> However, prior to this, Shorts had decided to undertake a successful practice, which had been performed with the earlier Empire flying boat, in producing a half-scale version of the aircraft, known as the S.31 (also known internally as the M4 – as per the title on the tailfin), to prove the aerodynamic characteristics of the design.<ref name = "norris 3"/> The S.31, which was largely composed of wood, was powered by an arrangement of four [[Pobjoy Niagara]] engines and featured a retractable undercarriage, operable bomb-bay doors, and other measures to realistically represent the larger production aircraft. It was constructed at Short's [[Rochester, Kent|Rochester]] facility.<ref name = "norris 3 4">{{harvnb|Norris|1966|pp=3–4}}</ref>

[[File:Short S 31 Half Scale Stirling.jpg|thumb|left|The Short S.31 half-scale testbed used for aerodynamic tests of the Stirling design]]
On 19 September 1938, the S.31 conducted its [[maiden flight]], piloted by Shorts' Chief [[test pilot|Test Pilot]] [[John Lankester Parker|J. Lankester Parker]]. Impressed with its performance, on 21 October 1938, Parker flew the S.31 to [[RAF Martlesham Heath]], [[Suffolk]], where it was evaluated by the [[Aeroplane and Armament Experimental Establishment]] and received mostly favourable reviews.<ref name = "norris 4">{{harvnb|Norris|1966|p=4}}</ref> There was one notable criticism amongst the feedback from pilots, being that the length of the takeoff run was considered to be excessive and that improvements would be desirable. Fixing this required that the angle of the wing to be increased for takeoff; however, if the wing itself were<!-- subjunctive --> modified, the aircraft would fly with a nose-down attitude while cruising (as in the [[Armstrong Whitworth Whitley]]); making this change was also complicated by the fact that work on the production line had already reached an advanced stage. Thus, Shorts lengthened the undercarriage struts to tilt the nose up on take-off, leading to its spindly gear, which, in turn, contributed to many takeoff and landing accidents.<ref>{{Harvnb|Winchester|2005|p=49.}}</ref>

The S.31 also received the lengthened undercarriage to test this; subsequent trials found no need for further modification in this respect.<ref name = "norris 4"/> Other modifications made included the adoption of a larger tailplane with conventional [[Elevator (aeronautics)|elevator]]s to improve aft controllability. The sole S.31 was scrapped after a takeoff accident at [[RAF Stradishall]], Suffolk, in February 1944. Meanwhile, before either of the prototypes had flown, the Air Ministry had decided to order the S.29 into production "off the drawing board" in response to reports of further increases in strength on the part of the German [[Luftwaffe]].<ref name = "norris 3 4"/>

On 14 May 1939, the first S.29, which had by this point received the [[British military aircraft designation systems#Names|service name]] "Stirling" after the [[Stirling|Scottish city]], performed its first flight, but on landing, one of the brakes locked, causing the aircraft to slew off the runway and the landing gear to collapse. The resulting damage caused the first prototype to be written off.<ref name="norris 3"/><ref name="hallp5">{{harvnb|Hall|1998|p=5}}</ref><ref name="Story p30">{{harvnb|Bowyer|2002|p=30}}</ref> A resulting redesign of the undercarriage led to substantially stronger and heavier struts being installed upon the second prototype. On 3 December 1939, the second prototype made its maiden flight.<ref name = "norris 3"/>

===Production===
Prior to the [[Munich Agreement]] of 1938, Shorts had received a pair of orders for the Stirling, each for the production of 100 aircraft; however, as a result of Munich, the [[Minister of Aircraft Production|Ministry of Aircraft Production]] (MAP) enacted 'Plan L', under which Stirling orders were rapidly increased to 1,500 aircraft.<ref name = "norris 7"/> In addition to contracts extending the projected work at [[Rochester, Kent|Rochester]] and [[Belfast]]; some of the additional contracts were placed with [[Austin Motors]] to be produced at their [[Longbridge plant|Longbridge facility]] and with [[Rootes Group|Rootes]], which were to manufacture the type at their new [[shadow factory]] in [[Stoke-on-Trent]]. At its height, manufacturing activity on the Stirling was being performed at a total of 20 factories.<ref name = "norris 7"/> According to Norris, while the aircraft's design had incorporated an inherent ability for production of the Stirling to be broken down, in practice, strict supervision of the work remained necessary.<ref name = "norris 7"/> To coordinate the dispersed production approach adopted for the Stirling, Shorts and MAP operated a travelling team of 600 production engineers and [[draughtsmen]] who routinely travelled throughout the United Kingdom to the manufacturing facilities involved.<ref name = "norris 7"/>

[[File:British WW2 bombers comparison.png|thumb|Diagram comparing the Stirling (yellow) with its contemporaries - the [[Avro Lancaster]] (blue) and the [[Handley Page Halifax]] (pink)]]
On 7 May 1940, the first production Stirling conducted its first flight.<ref name = "norris 4"/> According to Norris, initial rates of production were disappointing, and were in part due to delays in the delivery of machine tools and [[forge|forging]]s. It has also been alleged that production of the Stirling was negatively impacted by a decision by [[Max Aitken, 1st Baron Beaverbrook|Lord Beaverbrook]], the MAP, which had ordered a change in priority from four-engined bombers towards fighters and twin-engined aircraft to replace those lost during the [[Battle of Britain]].<ref name = "norris 7 10">{{harvnb|Norris|1966|pp=7, 10}}</ref> In August 1940, series production of the Stirling commenced at the Rochester factory.{{Citation needed|date=March 2017}}

Production of the Stirling was delayed by the ongoing bombing campaign of the Luftwaffe.<ref name = "norris 10">{{harvnb|Norris|1966|p=10}}</ref> The area, which included a number of major aviation firms, was heavily bombed in the opening days of the Battle of Britain, including one famous low-level raid by a group of [[Dornier Do 17]]s. A number of completed Stirlings were destroyed on the ground and the factories were heavily damaged, setting back production by almost a year. Some production was moved to Austin's Longbridge factory at [[Cofton Hackett]] just south of [[Birmingham]], the Longbridge production line eventually produced nearly 150 Stirlings.<ref>[http://www.austinmemories.com/page6/page6.html "Cofton Hackett production."] {{webarchive|url=https://web.archive.org/web/20120823143313/http://www.austinmemories.com/page6/page6.html |date=23 August 2012 }} ''austinmemories.com''. Retrieved: 27 December 2009.</ref>

From this point on, the Belfast factory became increasingly important, as it was thought to be well beyond the range of German bombers. However, Belfast and the aircraft factory were subjected to [[Belfast Blitz|bombing by German aircraft]] during the [[Easter]] week of 1941. To meet the increased requirement for its aircraft during the war, satellite factories near Belfast were operated at Aldergrove and Maghaberry, producing 232 Stirlings between them. In 1940, bombing damaged Supermarine's factory at Woolston and the incomplete Type 316 prototypes. In November 1940, development of the 316 was formally cancelled, leaving the Stirling as the only B.12/36 design.

The first few Stirling Mk.Is were furnished with Bristol Hercules II engines, but most were built with more powerful {{convert|1,500|hp|kW|abbr=on}} Hercules XI engines, instead.

===Proposed developments===
Even before the Stirling went into production, Short had improved on the initial design with the S.34 in an effort to meet specification B.1/39. It would have been powered by four Bristol Hercules 17 SM engines, optimised for high-altitude flight. The new design featured longer-span wings and a revised fuselage able to carry dorsal and ventral power-operated turrets each fitted with four 20&nbsp;mm Hispano cannons; despite the obvious gains in performance and capability, the Air Ministry was not interested.

In 1941, it was decided that the Stirling would be manufactured in [[Canada]] and an initial contract for 140 aircraft was placed.<ref name = "norris 12"/> Designated as the Stirling Mk.II, the Hercules engines were to be replaced by {{convert|1,600|hp|kW|abbr=on}} [[Wright R-2600 Twin Cyclone|Wright GR-2600-A5B Twin Cyclone]] engines; a pair of prototypes was converted from Mk.I aircraft. However, it was decided to cancel the contract in favour of manufacturing other aircraft; thus, no production Mk.IIs was ever completed.<ref name = "norris 12"/>

Shorts also pursued the development of the Stirling for potential use on the civilian market.<ref name = "norris 13">{{harvnb|Norris|1966|p=13}}</ref> Designated S.37, it was a full-furnished transport aircraft that was capable of seating 30 passengers and was constructed to conform with civilian standards. A single prototype, known as the ''Silver Stirling'', was converted from a Mk.V aircraft; however, partially due to greater levels of interest being expressed for a more promising civilian version of the Handley-Page Halifax, the proposal met with little official interest.<ref name = "norris 13 14">{{harvnb|Norris|1966|pp=13–14}}</ref>

In 1941, Short proposed the development of a new variant of the Stirling, the S.36,{{refn|Not to be confused with a prototype light aircraft that was built in 1912, which was also known as the Short S.36.|group=N}} which was nicknamed the "Super Stirling" in a company publication.<ref name = "norris 13"/> This aircraft would have featured a wing span of {{convert|135|ft|9|in|m|abbr=on}}, four [[Bristol Centaurus]] radials and a maximum takeoff weight of {{convert|104,000|lb|kg}}. The projected performance estimates included a speed of {{convert|300|mph|km/h|abbr=on}} and a {{convert|4,000|mi|km|adj=on}} range, along with a weapons load of {{convert|10000|lb}} over {{convert|2300|mi}}, or {{convert|23500|lb}} over {{convert|1000|mi}}. The defensive armament of the S.36 was to be an assortment of 10 [[.50 BMG]] machine guns that were set into three turrets.<ref name = "buttler 115 116"/>

The S.36 was initially accepted for testing under Specification B.8/41, which had been specifically written to cover the type, and an order for a pair of prototypes was placed. However, [[Arthur Harris]], as commander of [[RAF Bomber Command|Bomber Command]], felt that achieving bulk production of the type would take too much time and that the effort would be better expended on outfitting the existing design with improved Hercules engines with the aim of providing a higher operational altitude ceiling. While the Air Staff initially found the proposal to have some attraction, it was eventually decided to favour increased production rates of the rival Avro Lancaster, instead.<ref name = "norris 13"/> In May 1942, Shorts were informed that the Air Ministry would not be continuing the project; in August 1942, Shorts decided to terminate all work.<ref name = "buttler 115 116">{{Harvnb|Buttler|2004|pages=115–116}}</ref>