USAF JET BOMBERS The Birth of the Jet Bomber

war and there was an understandable reluctance to simply abandon them after so much time and effort spent perfecting their design.

The jet was unproven and its performance, though significant, was limited. Jet aircraft were exceptionally thirsty – severely reducing range compared to piston-engine designs. Early jets were unreliable too and needed high maintenance; in flight they were slow to spool up, making the aircraft sluggish at low speeds. German Me 262 pilots had found this out to their cost when they were mauled by marauding USAAF P-47s while trying to take-off or land.

Despite all these shortcomings, however, there were also undeniable advantages. Even in their rawest most undeveloped form, the weakest jet engines could provide speeds exceeding those of the very best piston engines and the jet had a higher ratio of cruise speed to top speed and became increasingly efficient with altitude, the reverse of the propeller-driven aircraft which needs dense air to bite on.

Where the piston engine was already at its peak, jet engine development had only just begun.

Competitors

During the early war years, the United States Army Air Corps had watched with growing interest as jet propulsion was developed in Italy, Germany and Britain but had assessed the competition as being largely a technological race rather than one which would have an immediate effect on combat capabilities.

The engine manufacturers themselves seemed disinterested in air-breathing reaction engines and while historians are uncertain as to exactly why this was the case, most agree that the lucrative market for reciprocating engines discouraged investment in questionable technology. And production of piston engines was now growing exponentially, driven by seemingly insatiable demand.

All that changed when British science adviser Henry Tizard visited America in September 1940 and told his US counterparts about progress made with the Whittle engine. In response to this, development of the jet engine in America really began in February 1941 with the establishment of the Durand Committee on Jet Propulsion.

Three companies were invited to build three separate types of gas turbine: Allis-Chalmers was to design a turbofan engine; General Electric, a turboprop engine; and Westinghouse, a turbojet. During a visit to Britain in March, General Henry ‘Hap’ Arnold, soon to be Commanding General of the US Army Air Forces, acquired access to the Whittle engine, the advanced development of which came as a surprise to the American delegation.

The GE engine development began after the secrets of the Whittle W.1X engine were known in detail. Based on that engine, first run on 18 April 1942, the

General Electric I-A produced a thrust of 1,250lb. When it was seen to run hot, during a visit to GE two months later, Frank Whittle recommended partitions in the blower casing to each chamber and that solved the problem.

The I-A engine powered the Bell P-59 Airacomet, America’s first jet fighter, and formed the basis for further developments applied to other prototype test-beds. When in production, the engine was redesignated I-16, reflecting its 1,600lb thrust output.

As intelligence reports came in about emerging jet fighter designs in Germany, and with the certain knowledge about Britain’s plans, the newly renamed Army Air Forces urged development of competitive jet fighters – more as development prototypes than definitive designs. But it was foreseen that the development of jet bombers would have to wait until engines with more power and better fuel consumption became available, since a successful bomber requires a decent payload capability as well as good range.

The Me 262, though, demonstrated that efforts to design and build a jet bomber could not wait. It was clear that any enemy armed with jet fighters would make quick work of lumbering pistonengine bomber formations. The drive for a jet bomber therefore began as early as June 1943.

The AAF pushed ahead on two fronts to make such an aircraft viable: firstly, more powerful jet engines were essential, and secondly an appropriately efficient airframe design was needed to attain the highest possible cruising speeds. Industry was incentivised to study both. Only by displaying financial commitment could the AAF get industry interested, accepting that they would be developing a production engine rather than a shortrun, experimental prototype.

With work already under way on jet fighter engines, GE was the company to go to, although it had been tasked with looking into turboprop designs, while Boeing was approached to come up with an airframe.

US Army Materiel Command was keen to push design studies for a bomber equipped with four GE TG-180 jet engines and AAF headquarters endorsed this decision in September 1943 when Boeing was given access to information about the Bell XP-59, at the time a highly secret project as was all jet engine research. Boeing openly expressed surprise that jet research had got as far as producing a flying prototype fighter and this mirrored the shock throughout the industry as word slipped out and the AAF revealed all.

Early Boeing studies were presented over the next two months and the chief of the engineering division at Wright Field concluded that “Contrary to the existing belief that jet-propelled aircraft