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Supermarine B.12/36 (Type 316)

Heavy Bomber Prototype Aircraft

This Supermarine bomber project was, itself, ended by German bombs dropped on the production facility in September of 1940.
Authored By: Staff Writer | Edited: 5/5/2019
National Flag Graphic


Year: 1937
Status: Cancelled
Manufacturer(s): Supermarine - United Kingdom
Production: 2
Capabilities: Ground Attack; Transport; X-Plane;
Crew: 6
Length: 73.49 ft (22.4 m)
Width: 97.01 ft (29.57 m)
Height: 21.98 ft (6.7 m)
Weight (Empty): 38,581 lb (17,500 kg)
Weight (MTOW): 59,007 lb (26,765 kg)
Power: 4 x Bristol Hercules HE 1.5M air-cooled radial piston engines developing 1,330 horsepower each.
Speed: 329 mph (530 kph; 286 kts)
Ceiling: 31,972 feet (9,745 m; 6.06 miles)
Range: 3,679 miles (5,920 km; 3,197 nm)
Rate-of-Climb: 800 ft/min (244 m/min)
Operators: United Kingdom (cancelled)
Specification B.12/36 was issued by the British Air Ministry in 1936 to cover a new, all-modern, four-engined heavy bomber for use by the Royal Air Force (RAF). Three designs came from this initiative which was eventually fulfilled by the Short "Stirling" (detailed elsewhere on this site). The other two submissions were the ultimately-abandoned Armstrong Whitworth B.12/36 and the Supermarine B.12/36, the latter which produced the related Type 316, Type 317, and Type 318 forms.

Supermarine went down in World War 2 history as the makers of the classic "Spitfire" fighter series and added a navalized form through its "Seafire" development. However, large aircraft types were not out of its design, development and construction scope and proven by the many flying boats the company put out prior to the conflict. Against the details of their proposed "Type 316" to fulfill Specification B.12/36, Supermarine was contracted for two prototypes in 1937.

The Air Ministry sought a four-engined type with a maximum bomb load of 14,000lb and a range out to 2,000 miles. Conversely, engineers could opt for a longer-endurance design of 3,000 mile range with a reduced internal bomb load of 8,000lb. Cruising speeds would reach at least 230 miles per hour when flying at about 15,000 feet and turrets would be featured for local defense against enemy fighters. Beyond its service as a heavy bomber, the airframe should also prove suitable for service in the transport role. Drive power was also given some leeway for either Bristol (Hercules) or Rolls-Royce (Merlins) were under consideration for finalized bomber production forms. This produced the "Type 317" (Hercules-powered) and the "Type 318" (Merlin-powered) variants. In the end, the Merlin-powered variant was given up for good - no doubt those engines badly needed in other more important types like Spitfire fighters.

By mid-August of 1937, Supermarine had delivered a mockup model for official review and the design was becoming promising enough to continue pursuit - particularly in light of foreign air powers finding considerable successes with their own four-engined heavy bomber types - up to this point the Royal Air Force held an affinity for less-complex bomber workhorses usually driven by a pair of engines. The death of lead engineer R.J. Mitchell (1895-1937) from cancer in June of 1937 proved a devastating setback for the program which still hoped to garner complete support from the Air Ministry going forward and Supermarine's preoccupation with Spitfire production only served to push the Type 317 program back even further.

Nevertheless, work on the prototypes continued but it was in a September 1940 Luftwaffe air raid that the future of the Type 317 was settled - German bombs landed squarely on the production facility which rendered the still-incomplete bomber prototypes a total loss. After a quick status review, the program was cancelled in full during November of 1940, bringing about an end to the promising venture and heavier reliance on the Short Stirling and other heavy bomber types that would soon join the RAF inventory.

As finalized, the Type 317 carried a large-area monoplane wing with rounded, tapered tips. The mainplanes were seated ahead of midships. The cockpit was added in stepped fashion, overlooking the nose, with excellent views of each engine pair found along the wing leading edges. The engines were housed in streamlined nacelles for maximum aerodynamic efficiency. The nose was slightly glazed to provide vision for the bombardier and a nose-mounted gun position. The fuselage then tapered rearwards and another gun position was located at the extreme end of the tail. The tail unit itself comprised a horizontal plane unit with rudders affixed at the edges, completing a "twin rudder" appearance common to many aircraft of the period. The undercarriage was of a conventional "tail dragger" arrangement with the main legs double-tired.

The Type 317 was designed to support a crew of six. Power was to be served from 4 x Bristol Hercules HE 1.5M series air-cooled radial piston engines developing 1,330 horsepower each. Dimensionally, the aircraft carried a wingspan of 97 feet and a length of 73.5 feet. Its service ceiling was estimated at 32,000 feet. Defensive armament amounted to 8 x 0.303in (7.7mm) machine guns located along various danger zones about the aircraft - at least two would be showcased at the nose and the tail. Internally, the bomb bay was cleared for carrying up to 7 x 2,000lb bombs or similar loads.


8 x 0.303in (7.7mm) machine guns in multiple defensive positions including the nose and tail sections.

7 x 2,000lb conventional drop bombs (or similar) load.

Graphical image of an aircraft medium machine gun
Graphical image of an aircraft conventional drop bomb munition

Variants / Models

• B.12/36 - Air Ministry Specification
• Type 316 - Original proposed bomber form by Supermarine evolving to become the Type 317/Type 318 offerings.
• Type 317 - Bristol Hercules-engined form eventually to serve as the production-quality model.
• Type 318 - Rolls-Royce Merlin-engined form eventually dropped from consideration.
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