Cancelled American bombers


From comically inept aeroplanes designed by overconfident charlatans to nuclear capable supersonic bombers that would have been all too effective in delivering doomsday, the US has created an exceptionally exciting armada of ‘almost-bombers’. By dint of their cancellation, it’s possible to appreciate these incredible machines without the stench of infamy that accompanies many operational bombers. Here are just some of them. 


Boeing XB-55 (1948, unbuilt) ‘Baby Bear’

Screenshot 2020-02-16 at 16.03.39

The XB-55 was a proposed strategic bomber powered by four turboprop engines driving contra-rotating propellers, so think smaller Tu-95 (it would have been ten metres shorter than the 46-metre Tu-95). It was powered by four examples of the Allison T40 – an early turboprop engine composed of two Allison T38 power sections driving a contra-rotating propeller via a common gearbox; the T40 powered a remarkable series of aircraft, including the Convair Tradewind and Pogo, Douglas Skyshark and the XF-84H Thunderscreech, among others. Turboprop engines were more powerful than piston engines and gave better range than the turbojets available at the time – but the use of turboprops would make it slower than the aircraft it was intended to replace, the B-47. Knowing the vital importance of the role, work on the XB-55 began soon after the B-47 had entered service.

The propeller manufacturer believed that the Allison T40-A-2 driveshaft would be able to withstand the forces caused by the extremely fast rotations of the propellers, but the engine manufacturer disagreed. Allison predicted it would take another four years to develop an appropriate engine. Technical arguments dogged its development, meanwhile the B-47 was demonstrating that pure turbojets were more reliable and efficient than predicted. At an Ohio conference lunch in 1948 it was suggested to re-engine another Boeing turboprop bomber concept, the Model 464, with J57 turbojets. This would lead to the XB-52, the aircraft that would become the (seemingly immortal) Stratofortress. The XB-52 was better than the XB-55 in every way, and the XB-55 was cancelled in 1949. 

Boeing XB-59 (1949, unbuilt) ‘Hustler tussler’


The 1949 cancellation of the XB-55 freed up funding for a far more ambitious bomber capable off flight at twice the speed of sound. Just how ambitious it was can be gleaned from the fact that no aeroplane actually reached Mach 2 for another four years! The design had a distinctive anhedral wing and a length of 37 metres. It was cancelled in 1952 in favour of the more compact Convair B-58 Hustler.

Douglas XB-42 Mixmaster (1944)Mixmaster Flash’


The remarkable XB-42 was in many ways the most advanced piston-engined warplane ever flown (though the Republic Rainbow might be a rival for this title). As René J. Francillon put it, “the XB-42 was as fast as the Mosquito B.XVI but carried twice the maximum bomb load…furthermore the Mixmaster had a defensive armament of four 0.50-in machine-guns in two remotely-controlled turrets whereas the Mosquito B.XVI was unarmed.” A variety of offensive gun options were considered including sixteen .50 cals or two 37-mm cannon. The XB-42A had a top speed of 488 mph and a maximum range of 4,750 miles. The Mixmaster was superb. But by the time the war ended the USAAF could afford to wait for the inevitable arrival of the jet bomber. The Mixmaster offers a tantalising insight into how military aircraft may have evolved if the piston age had lasted a little longer. douglas-xb-42.gif

Witteman-Lewis XNBL-1 Barling Bomber (1923) ‘Mitchell’s Folly’ 


The US military has a surplus of bile, and much of this is expressed through inter-service rivalry. The lamentable Barling Bomber benefited from this domestic squabbling, thanks to the cantankerous persistence of William ‘Billy’ Lendrum Mitchell. Mitchell was an Army general who had led US air combat operations in World War I. He was an ardent believer in air power, and in particular the ability of bombers to destroy battleships. This latter belief was heresy to the US Navy, and threatened the dogma that destroyers were unstoppable (and more seriously threatened to divert funds from the Navy to the Army). While the US Navy commissioned a series of secret tests to prove destroyers couldn’t be sunk by aeroplanes, Mitchell worked on some demonstrations to prove the opposite. Mitchell used Martin NBS-1 short-range bombers for these tests but clearly a large aircraft with an exceptional range would be better for the mission. Mitchell enlisted the help of the worst aircraft designer this side of Dr. William Whitney Christmas, Walter Barling (creator of the catastrophic Tarrant Tabor). Barling seemed to believe the best way to improve on the extremely large design disaster that was the Tabor was to make it even bigger.

Bundesarchiv_Bild_102-12879,_Gross-Bomben-Schlepper.jpgThe result was the largest aircraft in the world, a triplane with a wingspan seven metres greater than that of the Avro Vulcan! Not bad for 1923, except it was bad. In almost every metric it was pitiful – painfully slow, way shorter-ranged than the ‘short-range’ NBS-1 and underpowered and with more parasitical drag than St Pancras Station. Conceptually, it laid the way for the later large strategic bombers and with them the hundreds of thousands of dead civilians of Dresden, Tokyo, Nagasaki and the dozens of other targets that have suffered their devastating wraith.


Douglas XB-43 Jetmaster (1946) ‘Jetmaster not so flash’ 


The XB-43 was the first American jet bomber to fly. It came three years after the world’s first operational jet bomber, the German Arado Ar 234. If the XB-43 looks familiar it is because you have seen it above in its earlier life as the piston-engined Mixmaster. With its unswept flying surfaces and chunky fuselage it was an awkward halfway house between the piston and jet age – and was pushed aside by the superior North American B-45 Tornado.


Note the ‘Batmobile-style’ twin cockpits.


Martin XB-51 (1949) ‘No cigar for the silver cigar’ 

Blessed with one of the most exotic configurations of a wildly imaginative crop of experimental bombers from various manufacturers, the XB-51 was, frankly, a bit of a dud. Originally designed as a low-level bombing and close support aircraft, it wound up being considered instead as one of the options to replace the B-26 Invader as a night tactical bomber, alongside the North American B-45 and AJ-1 Savage, and the English Electric Canberra.

The XB-51 featured an engine installation unlike any other, with two General Electric J47 engines mounted in a ‘chin’ position on the fuselage sides, and a third located in the rear fuselage and fed by a dorsal intake. This arrangement enabled a very clean and thin swept wing to be mounted on the fuselage in a mid-wing position. The wing featured a large span slotted flap, full-span leading edge slats, and variable incidence.

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The story of a fantastically futuristic design losing out to a more conservative rival would be seen again in the YF-22/YF-23 ATF competition of the early 1990s.

The requirements called for a service ceiling of 40,000 ft, max speed of 550 kts and a range of about 1000 nautical miles, together with all-weather and night operation from basic airfields. Against this requirement, to quote ‘Post-World War II Bombers’ by Marcelle Knaack, Office of AF History, “The B-45 was too heavy, and the AJ-1 was too slow.”

The competition came down to a fly-off against the Canberra, which had created a sensation by flying non-stop and unrefuelled to the US from Europe – the first jet aircraft to do this.Screenshot 2020-02-18 at 10.52.11.png

In the fly-off, the XB-51 lost out to the Canberra, which could exceed the ceiling required by 15,000 ft, and offered double the required range. Although slightly faster at low level, the relatively high wing loading and low fuel capacity of the XB-51 meant that it lost out to the Canberra in range, ceiling and payload, despite appearing a far more futuristic design.

— Jim Smith 


Martin XB-68 (1954) ‘Steel-eye wingspan’


The extremely sleek XB-68 would have been largely built from steel to soak up the immense heat of flight at Mach 2.4. It was an extremely ambitious design, combining a very high top speed with a long range and a beyond state-of-the-art inertial guidance bombing and navigation system. This was pretty advanced stuff for 1954 and it was predicted to take until 1963 to get it into operational service. The USAF couldn’t wait that long and cancelled it in favour of the far more modest Douglas B-66 Destroyer.




Martin XB-16 (1934) ‘Twin-boom shake the room’

A 5,000-mile range, a 20% greater wingspan than the future B-29, a top speed of 237 mph and the look of an aircraft that was designed by an 11-year-old boy, the XB-16 was a 1934 proposal for a heavy bomber for the US Army Air Corps. Like the Mixmaster, it was powered by Allison V-1710 liquid-cooled engines (four). The engines were mounted in an unorthodox ‘push and pull’ tractor and pusher arrangement. The XB-16 was simply too slow to survive and didn’t progress further than some rather exciting blueprints. The US heavy bombers that actually did enter service where all equipped with radial engines. The design bears interesting comparison with two contemporaneous twin-boom aircraft, the Grokhovsky G-37 and Burnelli UB-14.


McDD/General Dynamics A-12 Avenger II (1991) ‘Cheney’s salty triangle’ 


In the late 1980s the US Navy wanted a long-range stealthy attack aircraft, one that could operate from aircraft carriers. McDonnell Douglas and General Dynamics responded with a radical design, the triangular A-12 Avenger II. The programme went very wrong, with huge technical shortfalls, delays – and cost and weight gains. Dick Cheney wanted to know why the project was going so badly and was given answers he did not consider clear or honest enough — and the axe was swung on the ‘Flying Dorito’ in 1991. The US government was keen for the contractors to pay back the $2 billion that had been spent on the project, but the contractors had other ideas. A lengthy court case ensued, one that extended into the following millennium! In January 2014, the case was settled with Boeing and General Dynamics agreeing to pay $200 million each to the US Navy. 


The Avenger’s remains.

Despite the huge success of the earlier F-4 Phantom II (as McDonnell) and the F-15 Eagle fighters, the 90s saw MD losing out: in the fighter field, its ATF contender failed to get to the contest finals. It then joined Northrop’s YF-23 offering, which lost in the finals to the Lockheed YF-22. MD also failed to win the JSF contract that led to the F-35. In the civil field its MD-11 was proving disappointing and the A380-like MD-12 proposal was pie-in-the-sky. McDonnell Douglas merged with Boeing in August 1997 with the latter as the surviving company.


The MD ATF contender.


If anyone benefited from the A-12 fiasco, it was General Electric. The A-12’s F412 turbofan grew into the F414, which was to power the aircraft that would perform the attack role in the A-12’s absence, the Super Hornet. The engine would also find gainful employment in the Gripen E/F and Korea Aerospace Industries KF-X.

Northrop XB-35/YB-35/YB-39 (1949) ‘Spirited away’


Northrop know how to play the long game. Since the 1940s they were trying to sell ‘all wing’ bombers but it wasn’t until the B-2 entered service in 1997 that they saw this dream come true. Northrop’s first flying wing bomber was the X/YB-35 which, coming in at the cusp of the jet age, was later re-engined as the jet-powered YB-49. Though jet engines increased speed to a respectable 520 mph (from the B-35’s 393 mph) this came at the cost of range – slashing it by half and effectively removing the aircraft from the strategic bomber class. Though a promising design with surmountable technical issues, it was cancelled in 1946. The project had eaten over half a billion 1946 dollars, equivalent to around 6.5 billion in 2020 dollars. Intriguingly, the later B-2 was to have an almost identical wingspan (the difference a matter of inches) and was created with the benefit of flight data from the YB-49. Today Northrop Grumman is working on a new flying wing design, the B-21 Raider.



North American XB-70 Valkyrie (1964) ‘Between a Ragnarok and a hard place’


Until the late 1950s everyone knew that each successive generation of bombers was faster and higher flying than the last. They had to be, as the fighters tasked with blowing them out of the sky were getting ever faster and higher flying. The next step was Mach 3, three times the speed of sound – or around 2,000 mph, at 75,000ft. The resultant aircraft was arguably the most impressive machine that ever flew: a sleek 56-metre-long white dart with a delta wing with outer sections that folded down by 65 degrees during high-speed flight. Despite its beauty, the B-70 fleet was designed to annihilate hundreds of thousands of civilians or highly protected nuclear missile silos with free-fall nuclear bombs. It was hoped that the bomber’s performance would render it invulnerable to manned interception, but it was soon clear that ever more potent surface-to-air missiles were a real threat. Intercontinental ballistic missiles were the future, but the XB-70 project had momentum.


The XB-70 became a political football kicked around by the most powerful men in America, including Nixon, Kennedy and McNamara, all adopting pro or anti positions as suited their needs. Kennedy was pro B-70 in the 1960 election campaign but once he won he changed his mind. The project swung back and forth from bomber to high-speed research aircraft. The unusual moniker came from a USAF competition to ‘Name the B-70’ which attracted 20,000 entrants. Over $1.5 billion in 1966 dollars (around 12 billion in 2020 dollars) was spent on the XB-70, making it perhaps the most expensive cancelled aircraft project of all time. 


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  1. kimmargosein

    Ahh, the Allison T-40. It seems the problem with the T-40 was it tried to keep turboprops relevant in the jet age. It also powered aircraft that the powers that be lost interest in quickly.
    Yes, Billy Mitchell versus the hidebound battleship admirals. Remember those target ships he sank were not moving, and not putting up any defensive fire.

    • Doc Squawk (@bogglesnatch)

      The T-40’s unreliability was a big part of the problem. The Thunderscreech had 12 test flights and 10 of them ended with a forced landing. It’s one of those engines that was so bad it not only died, it took down more than one aircraft program with it.

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