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Losing a Winner: The Supermarine B.12/36 Specification Type 317 Heavy Bomber


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“It is also interesting to look at one design that never got into the air; the Supermarine bomber. In designing the Spitfire Mitchell had pioneered a unique method of wing construction, the single spar with a thick metal leading edge. If this leading edge section could be filled with fuel it promised an aircraft with a very thin wing and slim aerodynamic fuselage while still having large fuel capacity. The Supermarine bomber (project B12/36) would have carried a bomb-load almost as great as a Lancaster at greater heights and at a speed close to the Spitfire! In short, the B12/36 could have given the RAF a bomber superior to every other W.W.II type except the B29 Superfortress.”

(Extract by John Dell, quoted by XyZspineZyX (2003))

 

 

The title of this topic applies to not one but two closely related events, the illness and death of Spitfire designer R J Mitchell and the premature end of his last aircraft design - a four-engine bomber that could have significantly strengthened Britain’s strategic hand in the Second World War. In 1933, Mitchell was operated on for cancer, but this was to prove unsuccessful and by early 1937, he was being seen less and less often at Supermarine. Nevertheless, shortly after the first flight of the Spitfire on 5 March 1936, Mitchell handed over the finalization of the Spitfire to the production team at Woolston, Southampton, giving him the freedom to engage in another innovative project during the final twelve months of his life - this project being for a heavy bomber to fulfil Air Ministry specification B.12/36.

The B.12/36 specification issued in 1936 called for a high-speed, four-engined, long-range bomber with a range of out to 2000 miles and a 14,000 lb bomb load or 24 soldiers; a longer-endurance alternative to this was also permitted of 3000 miles range with an internal bomb load of 8,000 lb. Cruising speed at about 15,000 ft was specified to be at least 230 mph. In addition to these basic requirements, the specification demanded a number of other more specialized criteria to be fulfilled. The aircraft had to be able to be broken down into component parts for transport by the existing railway system, and its wingspan was not to exceed 100 ft, mainly to save on materials and discourage “grandiose” time-consuming projects. Another restrictive requirement of the specification was that the bomber should be able to lift off from a 500 ft runway, clearing a height of 50 ft at the end; the specification therefore also included a requirement for catapult take-off capability, which could potentially extend the range and load capacity of the aircraft and allow it to use the small airfields then in current use. In terms of armament for local use against enemy fighters, the new bomber would have to have a retractable ventral turret as well as nose and tail guns, and it would need to stay afloat for several hours subsequent to being forced down into the North Sea or English Channel.

Supermarine was not the only company that submitted a design for specification B.12/36, and out of the various competitors, both Supermarine and Shorts were each to be awarded contracts for two prototypes even though there were aircraft companies such as Handley-Page and Vickers that had more experience with the larger, land-based, machines. Relevant in this choice is the fact that both Supermarine and Shorts were both experienced in producing water-resistant hulls, and Supermarine had just provided the RAF and Navy with the Stranraer and catapult-launched Walrus.

The first design tendered by Supermarine for specification B.12/36 was the Type 316, redolent of Mitchell’s ingenuity and with a deltoid wing shape (the leading edge being swept back but with a straight trailing edge), a wingspan of 93 ft (28.3 m), length of 71 ft (21.6 m) and a large single tail fin. In spite of the long wingspan, the proposed aircraft made use of a single spar wing supported by torsion-resistant leading edge boxes on a similar principle to that developed for the Spitfire fighter. Unusually for its time, fuel was to be carried in these leading edges which saved on weight, and the fuel tanks lent additional rigidity to the wing. Behind this spar component, the structure provided enough space for the main stowage of bombs, thus avoiding the need for conventional tiered bomb stowage which would have substantially increased both the cross-section of the fuselage and the consequential drag factor. Stowing bombs in the wing was not a wholly original Supermarine concept as the Polish PZL P.37 medium bomber had made use of bomb bays in the wing between the engines and the fuselage, as did the ultimately abandoned Armstrong Whitworth A.W. 42 design for the B.12/36 specification. However, Mitchell’s stowage of bombs in the wings was more extensive and was not to be adopted in any other front-line bombers in the Second World War. Supermarine were clearly concerned to maximize airframe efficiency and pay particular attention to reducing the bulk of the fuselage and frontal area. Estimates of the actual bomb load achievable in the Type 316 range from 14,000 lb (6350 kg) to perhaps as much as 21,000 lb (9525 kg), one reservation being that the bomb cells could not accommodate individual bombs exceeding 2,000 lb (907 kg). A further refinement in the design of the Type 316 was the proposal to place the required armament well-below the eyeline of the gunners, not only giving them a clearer view but also enabling a reduction in the cross-section of the turret and a faster traverse of the guns.

 

 

 

The stowage of bombs and fuel in the wings of the original Type 316 design (a feature that was carried over into the 317/318): Drawing 31600 Sheets 5/6 showing leading edge tanks and stowage of 29 X 250 lb/27 X 500 lb bombs (pic from johnkshelton.blogspot.com):

1944162885_bomberbombs.thumb.jpg.060e7ad22f7e29a0ea0163a79a35b025.jpg

 

 

 

Painting by John Dell of the Supermarine Type 316 heavy bomber as first designed by R J Mitchell, with attacking Heinkel 113 fighters (pic from spitfiresite.com and, below, ih3.googleusercontent.com):

xregina6.jpg.7e11946c42767f187f45601739830423.jpg

unnamed.jpg.d740caa28c30a634234dfd77d7352344.jpg

 

 

 

 

There was some flexibility in the choice of power plant for the new bomber, and at least five different engines for the Type 316 were put forward by Supermarine for consideration in the design stage - the Bristol Hercules HE1 SM, Rolls-Royce Merlin F, Napier Dagger E108, Bristol Pegasus XVIII, and Rolls-Royce Kestrel KV26. Of the five main contenders listed above, only the first three were of more than 1,000 hp (746 kw), while the lower powered engines were a backup proposal in case of failure in the development proposals of the larger engines. In fact, the Napier Dagger proved to be largely unsuccessful while the Bristol Hercules and Merlin engines went on to power many aircraft including the Stirling, Halifax and Lancaster bombers. It was estimated that with the more powerful engines in place, the Type 316 would have a maximum speed of 325 and 360 mph (523 and 579 km/h) and a cruising speed of 260 mph (420 km/h). The estimated operating ceiling was around 30,000 ft (9,144 m) and range was 3,000 mi (4,800 km) with its 2,500 gallon fuel capacity (these figures are from Wikipedia).

 

 

 

Illustration of the Supermarine Type 316 designed to meet Air Ministry Specification B.12/36 (pic from secrfetprojects.co.uk):

136556-79a9812f154fa2c2fb9b459bcac3f90d.jpg.2d6d01ea5c2df5226fde8f26547f5c7b.jpg

 

 

 

 

In late 1936, the different bomber proposals for specification B.12/36 were considered by the Air Ministry and although the Supermarine Type 316 did not immediately figure in the most favoured designs, both Supermarine and the Air Ministry initiated changes necessary to improve the position of the Type 316 such that it had become the the preferred design by January 1937. On 22 March 1937, the Air Ministry ordered two prototypes of the revised Type 316 bomber design, later to be dubbed the Type 317 with confirmation that it would be powered by Bristol Hercules engines (interestingly, the revised designs/drawings were originally executed under the heading of Type 316, with the 317 designation coming relatively late in the day).

It is at this stage in the proceedings that tragedy struck at Supermarine with the now terminal illness and death of the company’s chief designer, R J Mitchell. Towards the end of February 1937, Mitchell entered a London hospital where his prognosis was deemed to be poor, and a stay at the Cancer Clinic in Vienna was arranged in April. Letters bear witness to Mitchell’s despair at being unable to contribute further input into the design of the new bomber, but it became clear that this activity was not possible. Mitchell returned to Southampton on 25 May 1937, and he died on 11 June, aged just 42. The severity of Mitchell’s illness and the high probability of his premature death were instrumental in the Air Ministry decision to keep the Short S.29 proposal in play as a backup design to the preferred Supermarine option, and redesign work was requested by the Air Ministry. With Mitchell’s death in June, the Air Ministry placed an order for two prototypes of the Short bomber design, now competing directly with Supermarine and their Type 317.

The principal differences between the Type 316 and the reconsidered Type 317 reside in the tailplane and the area and shape of the wing, although there was other redesign work undertaken on the fuselage. Instead of the single tall tail fin, the 317 featured a twin tail; the tail unit itself consisted of a horizontal plane unit with rudders affixed at the edges, to form a “twin rudder” appearance common to many aircraft of the period. In terms of the wings, the wing surface was now 1,358 sq.ft (126.2 m²) as opposed to 1240 sq.ft (115.2 m²) in the Type 316, and the mainplanes were seated ahead of midships.Wingspan had been increased to 97 ft (29.6 m) and there was a noticeable shift in wing design towards a more eliptical wing platform. The sweepback of the wing was reduced from the Type 316 such that the trailing edge was no longer perpendicular to the travel of the aircraft, and in the 317 design the wing leading and trailing edges tapered almost equally towards rounded tips.

 

 

 

The main visual differences between the Type 316 and the revised Type 317 heavy bomber (pic from secretprojects.co.uk):

93613-f7d3daf199cbd9f05a8be9101e286c32.jpg.650624ff700ddc159ddc0c2a53142e20.jpg

 

 

Drawing of the proposed Supermarine Type 317 heavy bomber (pic from fullfatthings-keyaero.b-cdn.net):

317.jpg

 

 

 

 

The cockpit of the Type 317 was added in stepped fashion, overlooking the nose and with excellent views of each engine pair along the wing leading edges; the nose itself was glazed sufficiently to provide vision for the bombardier and a nose-mounted gun position. Moving rearwards from the cockpit, the fuselage was tapered and another gun position was located at the extreme end of the tail, giving an overall length of the aircraft of 73 ft 6 in (22.4 m), slightly longer than the Type 316. The number of crew members remained at 6, the same as in the Type 316, and the Bristol Hercules HE1 SM air-cooled radial engines also remained identical between the Type 316 and the finalized 317; these engines developed 1,330 hp at 2750 rpm, and in they were housed in streamlined nacelles for maximum aerodynamic efficiency, while the undercarriage was of a conventional “tail dragger” arrangement with the main legs double-tiered. Like the 316 before it, the Type 317 incorporated a retractable ventral (mid-under) turret that fired four Browning .303 machine guns with 1,000 rpg. Front and rear gun turrets could be equipped with two or four Browning .303 machine guns with 1,500 rpg, but the innovative low profile design of the front and rear turrets failed to reach the “final cut”.

 

 

 

Supermarine model of the Type 317 heavy bomber (pic from johnkshelton.blogspot.com):

blog3.thumb.png.7b3db9ffeb85fe7b191d76de24e26315.png

 

 

Side views of the three types designed by Supermarine for the B.12/36 specification - 316, 317, and as mentioned here below, the 318 with Merlin engines (pic from secretprojects.co.uk):

136554-185db5b8289f5f745e287abae6859734.jpg.b4bd040744fb6cbd39cc9342d1ff7535.jpg

 

 

 

It should be noted that Supermarine had also begun work on a Merlin-powered version of the Type 316 - designated the Type 318 - but the company was finally told in July 1937 to stop work on this variant and focus on the 317. It may be that the end of the 318 came about because of concerns about the availability of Merlin engines for what were considered more important aircraft types, such as the Spitfire. With the drawing up of the revised 316 design, which had morphed into the new Type 317, Supermarine could proceed to the mock-up stage, prior to the production of the two ordered prototypes.

On 12 August 1937, a fuselage mock-up was constructed and visited at Supermarine by Wing Commander McEntegard of the Air Ministry, from which assessment it was evident that the design - powered by Bristol Hercules HE1 SM engines - was promising enough to pursue, particularly in the light of foreign air powers having considerable success with their own four-engined heavy bomber types. Up until this point, the RAF had preferred the use of less complex twin-engined bombers. In October of 1937, Supermarine provided additional estimated performance figures for the new bomber - a cruising speed of 300 mph at 15,000 ft, and a stalling speed of 78.5 mph - and a visit from Supermarine executives to Bristol on 22 November helped to finalize certain details concerning the engines and their installation.

 

 

 

Painting by John Shelton of the Supermarine B.12/36 Type 317 as it would have looked in flight; sadly, I cannot find a larger image of this painting to show (pic from johnkshelton.blogspot.com):

451642379_Bombercopy.jpg.d91f2c163f6c2bce63da8c2ac4bcf09c.jpg

 

 

 

 

Although great progress had been made by Supermarine to bring the design of their new heavy bomber forward in preparation for the construction of the prototypes, things had started to become more difficult for the project, not least because of R J Mitchell’s death. Although the extent of disruption at Supermarine due to the untimely death of their chief designer has been debated, there is no doubt that it affected progress on the new bomber for the B.12/36 specifications, while not being the only reason why progress on the Type 317 was much delayed. A good summary of this is provided by Schneiderman on 3 March 2013 (in CAF-UK, started 2013) as follows:

 

“There are many reasons why the 317 was much delayed. Firstly Woolston underwent a huge expansion in the late 1930s and the Works were rather chaotic as they produced Stranraers and walrus [sic] while tooling up for the Spitfire. Remember, the production order for 310 aircraft was more than double the total number of aircraft they had built in the previous 20 years. The 317 was to be built at new works upstream, known as the Itchen Works while [sic, probably meant ‘which’] required new buildings.

Mitchell’s death was seriously disruptive, he had led the Design Office since 1919, and although he headed a talented team under Joe Smith in the Drawing Office and Alan Clifton in the Technical Office they were indeed rudderless for a time. Mitchell’s deputy, placed there by McClean when Vickers took over in 1928 [Vickers Aviation and Supermarine were absorbed to become Vickers Armstrong], was [H]arold Payne, but he had little design experience. There was a delay before Joe Smith was named as Mitchell’s replacement.

Preparing drawings and jigs for subcontractors on the Spitfire dominated the company’s business after 1936 and new projects, even potentially good ones like the 317, got pushed into the background.”

 

It is clear that work at Supermarine on the heavy bomber project was slow in the period following the Autumn of 1937. Indeed, twelve months after the meeting between Bristol and Supermarine, another set of figures was sent by Supermarine to the Air Ministry which, once again, showed slight differences to previous performance estimates. In these figures (taken from Andrews & Morgan, 1989/2008), top speed was estimated at 330 mph at 17,000 ft; maximum cruising speed 290 mph at 15,000 ft; service ceiling of 32,000 ft, and finally, range 1,980 miles at 179 mph flying at 15,000 ft with a 2,000 lb bomb load and a normal all-up weight of 44,000 lb. At the maximum overload weight of 59,000 lb the following figures pertained: range 3,680 miles at 202 mph at 15,000 ft with a bomb load of 8,000 lb, or 2,360 miles at 208 mph at 15,000 ft with maximum bomb load of 14,000 lb.

In January 1939, based on the final configuration of the Type 317 B.12/36 bomber, Supermarine claimed the following advantages from their Type 317 (quoted here from Andrews & Morgan 1989/2008):

 

“1. Fuel 2,500 gallons or 20,000 lb - considerably more than the whole aeroplane structure; 2. fundamentally the most efficient structurally; 3. straightforward to design and construct; 4. minimum maintenance; 5. reduction of fuel tank weight; 6. adaptable to modern requirements of locating as much load as possible in the wings; 7. resulting in a design of small size and low drag and hence high overall efficiency.

The cumulative effect of these advantages resulted in the Supermarine design being lighter, smaller and having a considerably higher performance than any other design submitted to the Air Ministry to the same specification.”

 

Interestingly, Supermarine had also not neglected that part of the B.12/36 specification referring to catapulting the aircraft; one of the last schemes considered for this being take-off from a ‘rail assister track’ rather similar to the method used later by the Germans for their V1 ‘Doodlebug’ flying bomb.

The two Supermarine prototypes were now under construction and there is an extant photograph dating to May 1939 showing a fuselage front. It had been decided that the prototypes of the 317 would be made at the Itchen Works, built to the modern designs of Oliver Percy Bernard on reclaimed land just upriver from the Woolston Factory; the Itchen Works opened in 1939 and was soon turned over to the production of Spitfire fuselages. Evidently, the pressure to build Spitfires was growing exponentially at this time, with continuing delays to production. The first RAF unit, 19 Squadron at Duxford, didn’t start receiving Spitfire Mk Is until 4 August 1938, with only 49 Spitfires having reached RAF units by 1 January 1939. Such intensity to keep supplies of the Spitfire (and other notable Supermarine aircraft) in train meant that the building of 317 prototypes was no longer a major priority and went on the back burner with work being executed haltingly on the construction of the two 317 prototypes.

In 1940, still with no completed prototypes having yet been built, disaster overcame the projected Supermarine heavy bomber, in the form of Luftwaffe bombing raids on the Woolston Factory and the Itchen Works. Before the dénouement of the Type 317 can be given, I must just explain that there is a certain vagueness or confusion in the sources used for this topic at this juncture in the story. Indeed, it proved difficult to work out exactly what was where and when with regard to the prototypes under construction at the time of the bombing raids in 1940.

The first of the 1940 raids on Supermarine took place in the early evening of 15 September 1940, when the Supermarine factory at Woolston and the nearby Thornycroft naval shipyard were attacked. Eighteen ME 110s, each carrying two bombs, attacked the factory directly but with a minimum amount of damage being done - a few windows were broken, although nine people in houses nearby were killed. On 24 September there were two raids on the Supermarine factory, at 1.50 pm and again, on a much smaller scale, at 4.15 pm. The first of these raids comprised 17 Me 110 aircraft achieving complete surprise by coming in fast and low. A total of twenty-nine high explosive bombs and one incendiary were dropped, out of which 17 bombs fell on the factory site, most of them landing in the mud of the river. The factory was largely unscathed but loss of life among the workforce - due to a direct hit on the railway bridge and an already occupied bomb shelter beneath a railway embankment - and nearby houses was high. Just two days later, on 26 September 1940, from 5.45 pm onwards, sixty Heinkel 111s of KG55 escorted by sixty Me 110 fighters attacked Supermarine in two waves. Fortunately, there had been some warning of the pending attack and the workforce were evacuated to the shelters. In spite of anti-aircraft fire, more than 70 tons of bombs were dropped, with seven bombs directly hitting the Woolston works and one hitting the Itchen works. The factory buildings at Woolston were so badly damaged that they were never rebuilt, and according to the Wikipedia account of this raid in the article on Supermarine, “Both prototypes of the Type 317 bomber and three complete spitfires were destroyed, while over 20 Spitfires were damaged.” The human cost of this raid were 55 dead and 92 injured. For future production of the Spitfire, it was fortunate that most of the important jigs and precision machines had either already been moved out of the Factory or were undamaged.

 

 

 

Front fuselage of a prototype 317 under construction before the destructive bombing at Supermarine in September 1940 (pic from destinationsjourney.com):

Image1-1.thumb.jpg.4ab273d98393247ae552e8c28a3511e0.jpg

 

A Supermarine type 317 prototype fusealge under construction before being destroyed by the Luftwaffe in September 1940 (pic from ww2aircraft.net):

200011641_supermarine-317mockup.thumb.png.0f4dba719c78db8a5fe5d0dd1b3ef422.png

 

 

 

 

In reading the Wikipedia account of the bombing raids on Supermarine, one is led to believe that the already constructed parts of the 317 prototypes of the new bomber were at the Woolston works even though these elements were apparently built at the Itchen works; there is no actual statement of fact as to their whereabouts. In two interesting posts by R6195, in CAF-UK et al. (2013/2014), there is a less ambiguous account which more strongly indicates that the constructed elements of the Type 317 prototypes were at the Woolston works at the time of the 26 September 1940 bombing raid when they were destroyed. In a post dated 2 March 2013, R6195 states the following:

 

 “I also have a recollection of talking a few years ago with one of Mitchell’s team about this bomber. Harry Griffiths was assistant to Arthur Black the company metallurgist and their laboratory and office were directly below Mitchell’s office at the works. Harry was there on both occasions when the bombing took place in September 1940 and he was of the opinion that the mock up of the bomber fuselage AND the Spitfire mock up were hanging from the rafters in one of the production areas and said both were destroyed. He also said that a completed bomber fuselage was also stored there and also destroyed. But wings had not been manufactured because of the great pressures on the company to manufacture Spitfires.

 ... ... ... ...

 As to the missing drawings of the Mitchell bomber. I believe most of the company drawings were saved in the bombing only to be burnt in the early 1960’s at Hursley Park near Winchester when Supermarine’s left there. Only a few early drawings of the Spitfire still exist in the archives at Solent SKY Museum in Southampton. Other than that it is off to Cambridge University Library that houses the extant Vickers archives, I suggest.”

 

 

In a further post on the thread, dated 5 February 2014, R6195 goes on to say:

 

“To slightly update my post 31 last year.....It is certain that a wingless and tail less(!) mock of Type 316 / 317 was made, hung from the roof structure (with the Spitfire mock up) and destroyed in the bombing that devastated “K Shop” at Woolston on September 26th 1940. However, TWO basic 316 / 317 fuselage structures were set aside also in K Shop and these were lifted in the bomb blasts and ‘bent’ around the vertical RSJ’s that formed part of the superstructure of that erecting bay.”

 

Contrary to the inferences gleaned from the above comes the following two quotes which clearly indicate that the prototype fuselages were destroyed at the Itchen Works on 26 September 1940. Andrews & Morgan (1989/2008) state that “Design and construction of the two prototype fuselages at the Itchen Works were nearing completion when the factory was bombed and both were severely damaged when the German Luftwaffe made a heavy daylight low-level attack on 26 September 1940.” To back this up, the article by soundnfury (2018) states that “work on the two prototypes went ahead at Supermarine’s Itchen Works. Unfortunately, on September 26, 1940, the works were bombed by the Luftwaffe and both prototypes - along with many of the detailed drawings - were destroyed”. I have concluded that the prototype fuselages and other elements relating to the Type 317 project were at the Itchen Works when they were destroyed and that part of the confusion comes from the term “Woolston” sometimes being used as a general term for the Supermarine works and HQ, covering both the Itchen and Woolston factories.

The bombing raid on 26 September 1940 was partly instrumental in the abandonment of the Supermarine Type 317 heavy bomber in November of that year after a brief Air Ministry assessment. The two reasons given for not continuing with the B.12/36 bomber project at Supermarine were the death of Reginald Mitchell and the bombing at Supermarine, but it is evident that the Type 317 project was already in trouble prior to the bombing in late September 1940, lagging behind the only other competitor remaining for the B.12/36 specification, the Short Sterling. Indeed, production aircraft of the new Sterling type reached frontline units in August 1940, before Supermarine had completed any prototypes of their 317. Andrews & Morgan (1989/2008) briefly discuss this finale of the B.12/36 competition as follows:

 

“The Short Sterling prototype, 1,760, first flew on 14 May, 1939, but on landing one brake seized and the aircraft was written off. Thus, of the four B.12/36 prototypes ordered [i.e. the two from Supermarine and two from Short], only one, 1,7605, was of use as a flying test-bed for development. The Sterling and B.1/35 Avro Manchester production lines were well advanced so the Air Ministry decided that Supermarine should concentrate primarily on the production and development of the Spitfire as well as on the Walrus, the Sea Otter and other promising projects.

  For comparison the Short Sterling had a maximum speed of only 260 mph, compared with the Supermarine design’s speed of over 300 mph, a maximum range of 2,010 miles compared to 3,000 miles at all-up weight at 54,900 lb, and bomb loads of 3,500 lb and 8,000 lb respectively. A total of 2,381 Stirlings was built but a projected production quantity at South Marston was cancelled.”

 

Andrews & Morgan also mention the Vickers contender for specification B.12/36, with its 135 ft wingspan and power from four Bristol Hercules HE1 SM engines. The Vickers machine would have had geodetic construction and although it failed to qualify in obtaining Air Ministry approval, its successor, the Vickers Windsor, designed for specification B.5/41, was built and three prototypes were flown. The conclusion that Andrews & Morgan come to as regards the whole matter of the Supermarine project for specification B.12/36 is that, “The detailed description of this project discloses the advanced thinking of R. J. Mitchell, particularly when considering his clever adaptation of wing space to house the major bomb and fuel loads to relieve wing bending loads and reduce ultimate weight, a feature of all modern long-range aircraft.”

 As something of a layman when it comes to a technical appraisal of a promising aircraft design’s potential in the field, I leave it to others more competent than myself to examine the designs and estimated performance statistics of the Supermarine Type 317 heavy bomber. Placing the 317 towards the top of the hit parade, we find Geofffrey Regan (1996) who says the following of the Type 317:

 

 “The fact that Britain never built this potentially great plane is one of the tragedies of the British war effort, which - it has been suggested - cost Bomber Command many thousands of lives lost in four-engined bombers like the Stirling whose specifications were so far inferior to the Mitchell design. More darkly, perhaps, the use of the Mitchell bomber would probably have cost the Germans heavier casualties during the area bombing campaigns. The projected speed of the Type 317 - as high as 370 m.p.h., which was at least a hundred m.p.h. faster than the Lancaster, Britain’s best bomber of the war - might have overwhelmed Germany’s night fighters and even proved too much for the Me-109 day fighters. This would have allowed Bomber Command to bomb during daylight, with a consequent increase in accuracy. The advantages of the high-speed bomber were demonstrated by the later Mosquito, though this was merely a light bomber. To have that much speed, as well as a capacity to carry an average of 14-17,000 pounds of bombs, would have provided Britain with the finest bomber of the whole war.”

 

I myself do wonder if Regan’s quite highly charged positive assessment is perhaps verging on exaggeration, given my overall reading of the subject matter. A more sober assessment comes from John Shelton (2012), in which he states that:

 

 ” More often than not, Supermarine estimates were actually achieved when their designs flew, but it will always be a matter of conjecture as to whether the extraordinarily competitive figures for Supermarine’s proposed bomber would have been attained - with an estimated speed close to that of the new fighters. It might, however, be maintained that, with the need for volume production - using standard gun turrets, and probably being forced to add a dorsal one too - the performance figures that the Supermarine bomber might have achieved would have been much closer to those of Britain’s actual four engined bombers.”

 

 As a final assessment in this article, I turn to colieghf, who posted the following piece on CAF-UK et al. (2013/2014) on 3 February 2014:

 

"It’d hard to imagine what would have happened at Supermarine if Mitchell had remained fit and healthy. The 317 probably had more potential than it’s given credit for. Although the wing looks quite thick, it actually isn’t. With the low aspect ratio the thickness/chord ratio is a lot less than the Stirling, also the wing section is NACA 2200 series, same as the Spitfire. A major reason for putting a substantial part of the bomb load in the wing was that this partially counteracts the bending loads on the wings and reduces structure weight. There’s little doubt that this was a more advanced structure design than the other heavies, including the Lanc.

 Clearly it wasn’t set up for blockbusters, grand slams or tallboys, but neither were B17s! It can only be conjecture now, but if Mitchell had still been around, if the prototypes hadn’t been destroyed, if the resources committed to the mediocre and expensive to build Stirling had been committed to the 317 instead, we might have been a lot better off. The use of radial engines wouldn’t necessarily have prevented it from being fast, the fastest Halifaxes were the late Hercules engined versions. There’s no doubt anyway that it could have used Merlins and if seen to be successful it may well have taken the place of the Halifax, so the engines would have been available. The later introduction of larger cased bombs would have been anyway handled by the Lanc, a faster more aerodynamically capable 317 alongside it could have given an excellent combination of strategic weapons, whereas the Halifax was more of a second rate alternative to the Lanc than a design of similar excellence but different capabilities. Mitchell’s early death was undoubtedly a national catastrophe, than heaven for what he did achieve, but it could have been so much more.”

 

 

References and Sources used for the Text of this Topic

 

Andrews, C. F. and Morgan E. B., “Supermarine Aircraft Since 1914”. Naval Institute Press (Putnam Aeronautical Books), 1989; a revised edition was published in 2008 by Brassey’s: Putnam Aeronautical. Pages 324 and 325 of one of these editions are reproduced by soundnfury (2018).

CAF-UK et al., “Supermarine Type B12/36, 317”, Key Aero Forums, 2013/14: Thread on the Historic Aviation Forum started 28 February 2013

Regan, Geoffrey, “The Past Times Book of Flying Blunders”, Guinness Publishing Ltd, 1996

Shelton, John K., “R J Mitchell and Supermarine: R J Mitchell’s Bomber and his death”, posted on Sunday 5 March 2017, online at johnshelton.blogspot.com/2012/07/r-j-mitchells-bomber-and-his-death.html

Soundnfury, “Supermarine Type 316 heavy bomber”, War Thunder Official Forum, 9 November 2018 in Great Britain. Online at: forum.warthunder.com/index.php/topic/432370-supermarine-type-316-heavy-bomber/&tab=comments#comment-7870362

Staff Writer, “Supermarine B.12/36 (Type 316): Heavy Bomber Prototype Aircraft”, Military Factory, last edited 5 May 2019. Online at militaryfactory.com/aircraft/detail.asp?aircraft_id=1524

Wikipedia, “Supermarine”, Wikipedia article last edited 5 April 2021. Online at en.wikipedia.org/wiki/Supermarine

Wikipedia, “Supermarine B.12/36”, Wikipedia article last edited 11 December 2019. Online at en.wikipedia.org/wiki/Supermarine_B.12/36

XyZspineZyX, “Another Great British ‘What Might have been...’, [Archive] Ubisoft Forums, “10-12-2003”. Online at forums.ubisoft.com/archive/index.php/t-27712.html

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