was to verify the echo reduction predicted by the scale tests. The project was code-named 'Passport Visa,' although the white-painted T-33 was better known as 'Bahret's White Elephant.'
The Passport Visa T-33 was completely covered with the RAM. This included the skin, wing tanks, and control surfaces. The plane was only an experiment, with no operational applications in mind. The air force test pilot selected for the project was Capt. Virgil 'Gus' Grissom. (The following year he was selected as a member of the first group of astronauts; he would later die in the 1967
Clearly, a plane's radar cross section could not be reduced simply by covering it with RAM. It would have to be designed in. Despite all these efforts, there was no simple way to calculate the radar cross section of a plane. With the computers and theoretical models of the time, too many factors entered into the calculation for it to be a practical possibility.
This meant designers would have to take a crude cut-and-try approach.
When Kelly Johnson wanted to test the radar cross sections of the A-12 and D-21, he first used small models. Then full-scale mock-ups were built and tested. From this data, the final designs were developed. Still, it was not until the planes actually took flight that the true radar cross section could be determined.
Such efforts could be made for Black airplanes. Reduced radar cross section had little impact on the design of operational aircraft. Until Vietnam.
The air defenses of North Vietnam required a fundamental change in tactics. A typical Rolling Thunder strike was composed of sixteen F-105D bombers. The force needed to protect them was made up of eight EF-105F 'Wild Weasels,' which attacked SAM sites, and six F-4D escorts against MiGs. Even though each F-105D carried individual ECM pods, two EB-66 jamming aircraft would also accompany the strike force. The EB-66s, in turn, each required two F-4Ds as protection against MiGs. Thus, to protect sixteen bombers, a total of twenty jamming and support aircraft were needed since the support aircraft themselves needed protection. [344] The net result was that most of the available aircraft were diverted from attack missions to defensive roles.
The revolution in air defense caused by SAMs would be underlined in the October 1973 Yom Kippur War. The Egyptian and Syrian armies that attacked Israel were equipped with the new SA-6 Gainful SAM. Mounted on a tanklike transporter, it could move with the frontline troops. The Israeli air force did not have the ECM pods needed to counter the SA-6 and suffered heavy initial losses. During a single strike against a Syrian SA-6 battery, six Israeli F-4Es were lost. The air defenses also prevented the Israeli air force from providing close air support to ground troops.[345]
Although the Israelis overcame the early setbacks, the SA-6 was a clear warning. As long as U.S. countermeasures and tactics were specifically tailored to enemy radars and SAMs, they would be vulnerable to technological surprise. The Soviets were then in the process of deploying a new generation of SAMs. In the event of a war in Europe, NATO forces could suffer the same huge losses as the Israelis had. Many academics theorized the end of manned aircraft was at hand. Technical advances in radar design, such as the traveling wave tube and computers, had increased power and the ability to defeat ECM. Any new technological advances in ECM would be countered by improved radars.
Others realized that a new set of assumptions was needed. Countermeasures had always been based on overpowering the radar. Even Black aircraft with reduced RCS — the A-12 and Model 147–154 drones — used ECM equipment for protection. The key was not more powerful ECM, but to make the RCS a primary design consideration. It would be eliminated, not simply reduced. With no echo, the radar would be blind. No radar would provide early warning as the aircraft approached; no radar would direct MiGs, antiaircraft guns, or SAMs. There would be no need for support aircraft. Air defenses would revert to the 1930s, against an enemy traveling at near supersonic speeds.
The problem was the amount of RCS reduction needed. A tenfold reduction would only shorten the range at which a plane could be detected. A hundredfold RCS reduction would merely degrade the effectiveness of radar. It would take a thousandfold reduction of a plane's RCS to make it undetectable to radar.[346]
Moreover, to be fully effective this reduction in RCS would have to be combined with other design features to reduce detectability. Just as the aircraft could not reflect any radar signals, it also could not emit any — no bombing radar or ECM transmissions. The infrared emissions from the engine would have to be hidden. The engine could not produce smoke. The airplane also would have to be quiet; the sound of a plane gives warning of its approach. The plane could not produce a contrail — this had been a major problem with the Model 147 drones. The final problem was visibility.
Although true optical invisibility was not possible, efforts had to be made to reduce the distance at which the plane could be seen. One problem was 'glints' from the canopy. A plane could be seen at a distance of five to ten miles; the reflection of the sun could be seen at a distance several times that.
The effort to make this possible became known as 'Project Harvey,' after the invisible rabbit in the play and film of the same name.[347]
In 1974, the Defense Advanced Research Projects Agency (DARPA) issued requests to five aircraft manufacturers to study the potential for developing aircraft based on a minimal RCS. They were to design a small, low-cost test aircraft to demonstrate the possibilities. It was called the 'XST,' for 'experimental survivable testbed.' The companies were General Dynamics, Northrop, McDonnell Douglas, Grumman, and Boeing.[348] All had recent experience with fighter design and manufacturing. Lockheed, which had not built a fighter since the F-104 program of the early 1960s, was not included.
By early 1975, Ben Rich had learned of the program. He had been involved with the work Lockheed had done on the Dirty Bird U-2s, the A-12, SR-71, and D-21, and knew it gave Lockheed the experience needed for the DARPA project. Rich obtained a letter from the CIA granting permission to discuss the reduced RCS work of the earlier projects. This was part of the request to DARPA for Lockheed to be included in the program. The effort was successful, and Lockheed joined the design competition.
The keys to Lockheed's efforts were Lockheed mathematician Bill Schroeder and Skunk Works software engineer Denys Overholser. They produced the conceptual
Schroeder went back to the basic equations derived by Scottish physicist James Clerk Maxwell a century before. These described how electromagnetic energy was reflected by a surface. Maxwell's equations were revised at the turn of the century by German electromagnetic expert Arnold Johannes Sommerfeld. For simple shapes, such as a cone, sphere, or flat plate, these formulas could predict how radar signals would be reflected. In the early 1960s, a Soviet scientist named Pyotr Ufimtsev developed a simplified approach which concentrated on electromagnetic currents set up in the edges of more complex shapes, such as disks.
The Maxwell, Sommerfeld, and Ufimtsev equations still could not predict the RCS for a complex shape like that of an airplane. Schroeder's conceptual breakthrough was to realize that the shape of an airplane could be reduced to a finite set of two-dimensional surfaces. This reduced the number of individual radar reflections that would have to be calculated to a manageable number. Rather than a surface made of smoothly curving surfaces, the whole airplane would be a collection of flat plates, which reflected the echo away from the radar. This system of flat, triangular panels became known as 'faceting,' because it resembled the shape of a diamond.
Schroeder asked Overholser to develop a computer program that could predict the RCS of a faceted aircraft shape. It took only five weeks for the Echo I program to be completed. Now, with the faceting concept and the Echo I program, it would be possible to predict the RCS of an aircraft. Possible designs could be tested and refined in the computer. The way was clear to build a truly invisible aircraft.[349]
The initial design was dubbed the 'Hopeless Diamond.' When Overholser presented a sketch of the design to Ben Rich on May 5, 1975, Rich did not quite grasp what had been achieved. Rich kept asking how big the radar return of a full-size aircraft would be — as large as a T-38, a Piper Cub, a condor, an eagle, an owl? Overholser gave him the unbelievable answer.
'Ben, try as big as an eagle's
