F-4X: The “Ghost” Fighter that defied speed limits

F-4X: The “Ghost” Fighter that defied speed limits

The legendary F-4 Phantom, recognized for its outstanding service in the US military for decades, continues to captivate nations to this day.

However, an ambitious idea sought to take it to new limits. In response to an unrivaled spy plane, the F-4X emerges, an aircraft that promised to be the fastest ghost fighter ever created. Let’s discover the details of this innovative proposal.


The successor to the McDonnell FH-1 Phantom of the late 1940s, the McDonnell Douglas F-4 Phantom II left its mark on aviation history after its maiden flight in 1958.

During the Vietnam War, it became the primary fighter bomber used by the United States Air Force, Navy, and Marines. Despite its imposing size, this aircraft was capable of a top speed of Mach-2.23 (1,711 mph).

The Legacy of the F-4 Phantom

With a maximum takeoff weight of 60,000 pounds, a fuselage length of 63 feet, a wingspan of 37 feet 5 inches, and a height of 16 feet 5 inches, the F-4 Phantom impressed with its combination of size and speed. Phantom pilot Dick Anderegg joked that this mighty aircraft proved that even a brick could fly if given enough thrust.

The challenge of the MiG-25

In the year 1971, during the Yom Kippur War, MiG -25 Foxbats, recognized as the world’s fastest interceptors, were flying over Israel on photo reconnaissance missions. Despite the efforts of the Israeli Air Force and its F-4s and surface-to-air missiles, it was impossible to hit the nimble MiG-25s.

The MiG flights, flown by Soviet airmen on behalf of Egyptian President Anwar Sadat, left a powerful impression on the Israelis.

F-4X: The “Ghost” Fighter that defied speed limits

The Israeli response

In response to this situation, the Israeli government decided to develop its own ultra-fast reconnaissance aircraft. They had a high-altitude reconnaissance camera, the General Dynamics HIAC-1, but its size required it to be transported in a Martin RB-57F, a reconnaissance version of the English Electric Canberra bomber manufactured under a US license.

However, this aircraft was not approved for export, and its top speed of just 570 mph fell well short of Israeli Air Force (IAF) requirements.

The Peace Jack Project

Fortunately, events took a favorable turn. In 1971, the United States modified its aeronautical export policy. The US Air Force had developed a module called G-139, which allowed the HIAC-1 camera to be housed under the fuselage of an F-4 Phantom.

However, the chamber was so large that the capsule was more than 6 meters long and weighed more than 4,000 kilos.

The F-4X Concept

This camera-pod combination was used on numerous reconnaissance flights, known as “Bench Boxes,” near the North Korean border, installed under F-4C Phantoms. The IAF showed interest in the camera-equipped Phantoms, which gave birth to Project Peace Jack. One of the main concerns was how the enormous weight of the camera would affect the performance of the aircraft.

General Dynamics engineers concluded that the best way to address this challenge was to increase the F-4’s performance rather than design a lighter camera system.

F-4X: The “Ghost” Fighter that defied speed limits

Proposed improvements

Thus the concept of the F-4X was born. This aircraft would feature large 300-gallon conformal tanks mounted on the engine fairings of the fuselage.

Demineralized water would be used for the pre-compressor cooling (PCC) of the General Electric (GE) J79 engines, which was estimated to increase the thrust of the engines by 50%.

Tests and limitations

In 1973, an updated and smaller version of the HIAC-1 camera was developed, allowing it to be mounted on the nose of the Phantom. This combination of increased engine thrust and reduced drag would theoretically increase the F-4’s cruise speed to Mach-2.4, with a top airspeed of Mach-3.2. These figures placed this aircraft on par with the best combat aircraft in history.

However, after extensive testing, the General Dynamics research and development team concluded in 1975 that the apparently beneficial PCC procedure caused the turbine compressor blades to swell, resulting in catastrophic damage to the turbine. Engine. Also, at the time, McDonnell Douglas was finalizing the F-15 Eagle test program, which had priority.

The fate of the F-4X

Lastly, the US State Department feared that the Israeli Air Force would use the F-4X to shoot down a Soviet reconnaissance plane, potentially triggering an international incident. Thus, the F-4X’s death warrant was signed.

Despite its non-realization, the F-4X remained a milestone in the history of military aeronautics. His bold proposal, focused on improving the performance of a legendary aircraft, showed how far the limits of speed could go in the field of aerial combat. The F-4 Phantom, with its unmatched legacy, continues to be an unsurpassed benchmark in military aviation.