Few aircraft have reached the legendary status awarded to McDonnell Douglas’ F-4 Phantom II. Developed into a jet that would play a deciding role in many conflicts around the globe, this was the very image of advanced fighter aviation. Though the type’s first impressions were not up to par, further development would lead to the F-4E, which is widely regarded as the best all-around iteration of the Phantom. Nicknamed the “Rhino” by US Air Force aircrew, the F-4E packed quite a punch with its powerful AN/APQ-120 radar, two powerful General Electric J79 engines that could push it to Mach 2.2, and an internal M61 Vulcan cannon.
In the late 1960s and ’70s, the US had been marketing the Rhino; despite its somewhat lackluster performance, it had quickly attracted interest from many countries, especially Israel. There the IAF ordered a fleet of F-4E and RF-4E recon Phantoms, dubbed the “Sledgehammer.” Israeli pilots loved the F-4E; to them, it was fast, versatile, and easily able to outrun Soviet export fighters flown by the Arab neighbors.
The RF-4E Raven, on the other hand, was the Israeli version used for reconnaissance; it was this particular type of aircraft that was severely put at risk. Cameras fitted in the Raven required the aircraft to overfly hostile territory to produce high-resolution photographs; as such, it was highly susceptible to SAMs. Israel needed a camera platform with LOROP so that it could continue observing the Sinai and Egypt without exposing itself to hostile air space.
General Dynamics responded by offering to modify existing F-4Es into a new variant that would give it a Mach 3+ capability. This would be achieved by the addition of two large conformal tanks carrying 2500 gallons of water each for water injection—a process known as pre-compressor cooling (PCC). This would cool the air going into the engines to permit the Phantom to achieve a sustained speed greater than Mach 3.
Initial interest was shown by the US Air Force, but this rapidly faded when it decided to procure the high-performance McDonnell Douglas F-15A instead. In addition, the State Department objected to the export of such advanced technology; any exports in this regard could compromise strategic balance and possibly pose a threat to intelligence gathering by the SR-71 Blackbird.
To get around this export embargo, General Dynamics offered a version without armament, fitted with the HIAC-1 LOROP camera in the nose. This version was not the fighter that Israel wanted but it suited their reconnaissance requirements. In 1974, the IAF provided an F-4E to General Dynamics to be modified into an RF-4X prototype.
Even with its promising modifications, such as redesigned air intakes and the most sophisticated PCC system ever designed, the project was shaken at its root by a variety of problems. Among other things, the engineers discovered that PCC would cause the turbine compressor blades to grow and crush into the engine case, resulting in catastrophic failure. Additionally, the imminent emergence of the F-15 Eagle and doubts about the RF-4X’s prospects as an interceptor made axing the program a fait accompli.
Although the RF-4X itself never flew, the IAF still gained from this program. Three Phantoms were converted to the RF-4E(S) variant, equipped with the HIAC-1 camera in the nose. Nicknamed “Tsalam Shablul” or “Photographer Snail,” these aircraft flew reconnaissance missions at altitudes approaching 70,000 feet, serving the IAF until their retirement in 2004.
The RF-4X story is one of relentless technological progress, coupled with the complex interplay of military needs, international politics, and engineering difficulties that set up its background. While the fastest Phantom never got off the ground, its legacy lives on in aviation history.