operational fighters and bombers. They, like the B-17s and Lancaster bombers of World War II, relied on conventional countermeasures packages to overcome air defenses, as well as such techniques as flying through gaps in radar coverage and attacks on air defense sites. With the start of the Vietnam War, the threat again changed. In addition to interceptor aircraft and anti-aircraft guns, U.S. aircraft now faced SAM missiles.
SAMs were initially a difficult challenge for tactical aircraft. What was needed was the means to defeat a weapon that was faster than a conventional jet fighter, and which was guided to the target aircraft by radar. The technology necessary existed, although it took time to develop. This involved improved countermeasures, Wild Weasel aircraft to suppress the SAMs, and, finally, maneuvering to avoid any incoming SAMs.
These proved effective in Vietnam, but following the war there was a split in the assessment of the future threat. Even with the proliferation of new Soviet SAMs, and improvements in radar technology, the opinion in the tactical units was that countermeasures, Wild Weasels, and maneuvering could still overcome the threat posed by any new enemy air defense. They were 'Manly Men,' who could out fly SAM's, given the proper warning. The need, as they saw it, was more of the same— improvements in the existing technology.
Others had a different opinion. Their threat assessment was not based on U.S.
success against SAMs in Vietnam, but, rather, on the Israeli failure in the 1973 Yom Kippur War. The threat they saw was that countermeasures were susceptible to technological surprise when faced with the multi-layered, interlocking network of SAMs, radars, and guns that the Soviets and Third-World countries were deploying. What was needed against this threat was not the kind of incremental approach that the tactical units wanted, but, rather, a whole new approach. What was needed was what had long been part of the earlier Dark Eagles, a reduced RCS. To be effective, however, a level of reduction was needed which was of a magnitude greater than that achieved with the U-2 and A-12.
This also required a change in outlook. Because of the A-12 and SR-71, the assumption had been that the key to survival was ever-greater speeds and altitudes.
The CIA had considered such possible high-speed replacements for the A-12. In mid-1964 General Dynamics completed a feasibility study called Project Isinglass, which proposed an aircraft able to reach Mach 4 to 5 at
In the face of the threat of improved SAM systems, this faster and higher assumption had to be turned on its head. Such speeds were incompatible with stealth, due to the sonic boom and infrared energy the vehicle would produce. Rather than hypersonic, or even supersonic speeds, stealth required a subsonic vehicle. Its operating mode would be like that of a submarine. Just as a submarine relies on silence while cruising slowly in the depths of the sea, a stealth aircraft would have to use a similar philosophy to conceal itself in the sky.
The question was one of whether the technology existed to create a truly invisible aircraft. In the two decades since Kelly Johnson had begun Project Rainbow, the goal had proven to be as elusive as a rainbow's end. How it was finally accomplished illustrated the changes made in those intervening years, including who made the innovative discoveries, how they did it, and the tools they used.
While Eisenhower's scientific advisers on the U-2 and A-12 included Nobel Prize winners, the stealth breakthrough did not came from academic scientists, but, rather, was made by a pair of 'computer nerds': Bill Schroeder, a Lockheed mathematician, and Denys Overholser, a Skunk Works programmer. To create a stealth aircraft, Schroeder turned the aircraft design process inside out. Kelly Johnson, in building the U-2, A-12, and D-21, started by designing an aerodynamic shape that could fly, then tried to reduce its RCS. What Schroeder did was to make the conceptual breakthrough that a complex shape such as an airplane could be simplified to a finite set of flat surfaces. In effect, he designed a shape with the smallest possible RCS, then tried to make it fly. Overholser made this possible with a computer program to calculate an airplane's RCS. This was far more efficient in the initial design stage than pole testing a model, and allowed the shape to be modified in the computer.
The result, the 'Hopeless Diamond,'with its wings made of flat plates, would never have occurred to an aerodynamicist. To an aerodynamicist, this was heresy.
Airplanes were streamlined; they had curved surfaces. Wings are not made up of flat plates, they had curved surfaces. But this was not about aerodynamics; it was about electrical engineering.
Yet all Schroeder's and Overholser's work would have meant nothing without another technological advance. Despite its strange shape, the Hopeless Diamond was structurally similar to a conventional aircraft. Had the shape been discovered in the 1960s, the basic airframe could have been built, but it would never have flown. The Hopeless Diamond shape was aerodynamically unstable. The aircraft stability control systems which existed in the 1960s, even the one developed for the A-12, could not have coped with the Hopeless Diamond. It was not until the early and mid-1970s that the multi-axis computer control systems necessary for such an unstable vehicle were developed. It was the computer revolution that made stealth a reality; without computers it would not have been possible to calculate the radar cross section of a given shape, or to make it controllable.
By early 1977 two prototype stealth aircraft were being built under the code name 'Have Blue.' The program had now become the most closely guarded secret since the Manhattan Project of World War II. Despite the loss of both of the Have Blue aircraft during the test program, the RCS test results were phenomenal. Stealth had arrived, and with it a revolution in Air Power.
What then of the future of stealth? Contrary to popular opinion, predicting the future is easy. In the mid- 1950s, for example, it was confidently predicted that ballistic missiles would make manned aircraft obsolete. It was also predicted that we would now have flying cars.
The problem is that the political, technical, and social factors which influence the future are so unpredictable as to border on the irrational. Another problem is that we tend to imagine the future as a direct projection of the current moment, rather than looking to the past to see how far we have come and the ongoing trends which have brought us here. To illustrate this point requires a thought experiment.
Imagine for a moment it is the mid-1950s. Forget all that will happen in the next four decades. In the world you know, Eisenhower is President, Elvis is king, both televisions and countermeasures use vacuum tubes, the transistor is still experimental, a computer is a huge mainframe unit which takes up a room, the B-52 is just entering service, airliners use propellers, the launch of the first satellite is still in the future, a manned flight to the Moon is the definition of the impossible, books are written on a typewriter and calculations are done with a slide rule. A technological prophet announces that:
I predict that in forty years, computers will be sold in stores and will be as commonplace as televisions are in the 1950s. These computers will fit on a desktop, while others are small enough to sit in your lap. All these computers are vastly more powerful than any existing 1950s mainframe computer. Many are bought by parents for their children to do homework. Publishers require books to be prepared on these computers; the typewriter is obsolete. These computers are linked together by a communications system called the 'Internet' which allows you to send messages and do research at universities, libraries, and other institutions anywhere in the world.
If this had really been said to a mid-1950s audience of people working in the electronics field, they would have thought the speaker was out of his mind. Yet the technical, political, and social trends that would create the PC were already developing.
Having given this cautionary tale, it has to be said that the future of stealth is a reflection of its past. Have Blue was built with the sole purpose of finding out if stealth would work on a real airplane. Stealth was the only design consideration.
In the design of the F-117 A, the basic Have Blue shape was retained. A few changes were made to correct defects found in the Have Blue, and to accommodate operational equipment. Despite this, in the F-l 17A, stealth superseded other design considerations such as range or payload. It was a short-range, light attack aircraft. With the B-2, the situation is more complex. As with the other early aircraft, stealth came first. However, its stealth capabilities had to accommodate the long range and large payload of a strategic bomber.
Each was a highly specialized, single-mission aircraft. They had also been built under the tight secrecy which enveloped stealth from the late 1970s to the end of the 1980s. The effect of this secrecy was to make stealth a highly specialized concept, one that seemed to apply only to a narrow set of missions, rather than to aerospace
