Few aircraft have reached the legendary status given to the McDonnell Douglas F-4 Phantom II. From an innovation standpoint, this jet not only ushered in a new era of fighter aviation but also flew sorties over several conflicts worldwide. Through the rough trials of its early development, the F-4E variant became the most multi-niche variant and was lovingly referred to as “Rhino” among US Air Force aircrew. Equipped with a powerful AN/APQ-120 radar and General Electric J79 engines, this beast could push things up to Mach 2.2, with an M61 Vulcan cannon internally mounted. The Rhino rapidly gained international interest. By the late 1960s and ’70s, eleven countries, including Israel, flew F-4E and RF-4E.
The F-4E, known as the “Sledgehammer,” became a key element of the Israeli Air Force (IAF). It was fast, Israeli pilots found, and the aircraft could do nearly everything; it could even outrun Soviet-export fighters flying with neighboring Arab states. The RF-4E “Raven” furnished much-needed aerial reconnaissance, though it came with limitations. Unlike the high-flying SR-71 Blackbird or U-2 Dragon Lady, the RF-4E had to fly into contested airspace to capture detailed images, rendering it vulnerable to surface-to-air missiles.
The SAM threat grew exponentially in the late 1960s and early 1970s, much of it from Egypt. That country had received huge amounts of Soviet support, and by the end of the 1967-1970 War of Attrition, an advanced SAM network had been established, through which some Israeli F-4Es had already been shot down. This was an emergency such that it warranted a new kind of reconnaissance solution that would function from the safety of Israeli airspace.
Things only got worse with the introduction into Egypt of the Soviet Union’s MiG-25R Foxbat-B reconnaissance aircraft in 1971, which flew at Mach 2.83 and, in emergencies, even Mach 3.2. With such opponents, an important problem became posed for the IAF. However fast, no F-4 could catch up with a Foxbat.
General Dynamics now had an answer: to turn existing F-4Es into a new variant capable of Mach 3+ speeds; this would involve large conformal tanks carrying 2500 gallons of water for pre-compressor cooling. The concept called for water injection into the engine inlets, cooling the air and thereby boosting thrust. General Electric, the manufacturer of the J79 engine, was somewhat skeptical about the proposal but did assist with research reviews.
Tests run at the Arnold Engineering Development Center were also positive for the project. With PCC, an F-4 could hold its afterburners in operation longer and achieve speeds over Mach 3. Redesigned air inlets and controllable intake ramps also improved performance. An F-4X, a Phantom that could sustain over three times the speed of sound in dashes and cruise at Mach 2.4, was the result.
However, the US Air Force lost interest in the F-4X when it realized it was going to get the high-performance F-15A. The State Department did not want to export such advanced technology abroad for fear of compromising the SR-71 intelligence-gathering capabilities. To bypass the export ban, General Dynamics offered a disarmed version, the RF-4X, fitted with the HIAC-1 LOROP camera.
In 1974, Israel loaned an F-4E to General Dynamics to be converted into an RF-4X prototype. As it happened, the engineers who had been desiring to develop the PCC system needed more time; the USAF withdrew from the project; and Israel’s efforts were not adequate in itself. The fastest Phantom in history never took to the skies and was doomed to remain one of the most tantalizing “what ifs” in aviation history.
It wasn’t a total loss for the RF-4X program; in good time, Israel received three RF-4E(S) reconnaissance planes equipped with the HIAC-1 camera, which served until retirement in 2004. It is the story of the F-4X that serves as evidence and testament to the human battle within to keep improving military aviation technology.