Key Points and Summary – Debates over whether America “needs” a sixth-generation fighter often start from the wrong place: the generational labels themselves.
-Dr. Robert Farley traces how the 1st-through-5th-generation scheme emerged in the 1990s to capture big leaps from the Me-262 to the F-22 and F-35, then grew fuzzy with upgraded 4.5-generation jets.
A F-15EX assigned to the 85th Test and Evaluation Squadron, Eglin Air Force Base, Florida, flies behind a KC-135 assigned to the 465th Air Refueling Squadron, Tinker AFB, Oklahoma, Oct. 15, 2021. In-air refueling allows fighter aircraft to stay airborne for longer periods of time without having to land to refuel. (U.S. Air Force photo by 2nd Lt. Mary Begy)
A U.S. Air Force KC-135 Stratotanker offloads fuel to U.S. Air Force F-15 Strike Eagles over the U.S. Central Command area of responsibility, April 11, 2025. The F-15E is deployed to the CENTCOM AOR to reinforce regional stability and deter aggression from violent extremist organizations.. (U.S. Air Force photo by Senior Airman Keegan Putman)
-Now, with sixth-generation projects like the F-47 and Chinese test aircraft, the definition is even less clear, even as drones, networking, and sensors drive real change.
-Farley argues it may be time to treat “generations” mainly as history and refocus on which concrete technologies airpower actually needs.
Fighter ‘Generations’ Were Useful History – Now They’re Blocking Clear Thinking
Does the United States need a sixth-generation fighter jet, or will its fifth-generation fighters be enough to meet its needs in the following decades? Can 4.5-generation fighters fill capability gaps?
And what should the military services do with the legacy fourth-generation fighters that fill out the remainder of the U.S. fleet?
Questions like the above are frustrating enough to some within the U.S. Air Force and the defense industry to spur a rethink of the classification scheme that divides fighter-jet technology into “generations.”
The argument is that the generational scheme is muddling clear thinking about the technology and should be abandoned as anything other than a tool of historical analysis.
The analytical community uses such classifications because they are useful. When they cease to be useful, we stop using them. After five generations of jet fighters, have we finally reached that point?
An F-15C Eagle assigned to the 44th Fighter Squadron returns from a training sortie at Kadena Air Base, Japan, Dec. 20, 2022. The 44th FS maintains combat readiness through daily training, ensuring the ability to provide superior airpower capabilities in support of a free and open Indo-Pacific. (U.S. Air Force photo by Senior Airman Jessi Roth)
Origins
Several classificatory schemes began to emerge in the 1990s in an unwitting collaboration among historians, analysts, and industry. The schemes tried to capture the critical moments of technological tumult that erupted during the 1940s, 1950s, and late 1960s, while also trying to explain long periods of incremental innovation.
The schemes weren’t identical but resolved into a more or less common usage in the 2000s. Of course, any effort to draw borders invariably creates borderline cases, and the generational approach to fighters is no different.
The Fighter Generations
Generally speaking, the first generation of jet fighters includes such aircraft as the German Me-262 and the Lockheed P-80 Shooting Star—subsonic aircraft with conventional gun armament that entered service before 1950. The second generation first saw combat during the Korean War.
Fast, swept-wing F-86 Sabres and MiG-15s dueled over the peninsula, and these jets were also armed with conventional guns. This generation led into an intense period of technological innovation in the 1950s.
At the dawn of the third generation, classification becomes murkier. The first and second generations were both short-lived, with most aircraft rapidly aging into obsolescence. Not so for the third generation. Aeronautics engineers had perfected their craft, and technologies had matured to the point that aircraft enjoyed more staying power.
U.S. Air Force Capt. Aimee “Rebel” Fiedler, F-16 Viper Demonstration Team commander and pilot, flies at the Stuart Air Show, FL, Nov 11, 2023. The F-16 Fighting Falcon is capable of speeds of up to mach 2 or twice the speed of sound. (U.S. Air Force photo by Staff Sgt. Dallin Wrye)
A U.S. Air Force F-16 Fighting Falcon piloted by Maj. Josiah “Sirius” Gaffney, Pacific Air Forces’ (PACAF) Demonstration (Demo) Team commander, sits on the tarmac shortly after landing during the PACAF F-16 Demo Team Practice Flight at Misawa Air Base, Japan, April 21, 2021. Although COVID-19 has postponed air shows, the demo team continues training to make sure they are ready to showcase the F-16 capabilities. (U.S. Air Force photo by Airman 1st Class Leon Redfern)
The third generation of jets was supersonic (many airframes could reach Mach 2) and generally carried both air-to-air missiles and gun armament.
Jets with sufficient speed, payload, and maneuverability could be updated with new weapons and electronics that made them competitive even with later fighters. Indeed, third-generation fighters remain in service today, albeit in dwindling numbers. Classic third-generation fighter jets include the U.S. Century Series, the MiG-21, the F-4 Phantom, and the French Mirage.
Fourth-generation aircraft served alongside many third-generation fighters. Designers of the new aircraft applied lessons learned from the third generation to produce a revolution of increments; the F-15 and F-16 were better than their predecessors, but not transformational. Like their third-generation ancestors, fourth-generation fighters have staying power—many production lines are still open today.
The fifth generation produced a sharp definitional break. Perhaps because the generational scheme came into existence around the same time as the first fifth-generation fighters became operational, answers to the question of what made the latest aircraft different were uncommonly clear.
Fifth-generation fighters have stealth, supercruise, and sensor fusion. Those attributes define what makes an F-22 different from an F-15 and what makes an F-35 different from an F-16. Of course, newer fourth-generation fighters could be modified to adapt some of the characteristics that distinguish the fifth generation.
Thus emerged the monstrous “generation 4.5” term to describe the most advanced Gripens, Rafales, and F-15EXs.
Sixth Generation Fighter
The sixth generation is arriving now, although its only representatives so far include the U.S. F-47 and several Chinese test aircraft. Sixth-generation fighters are a lot like fifth-generation fighters but are better in ways that often seem to defy description.
Most analysis suggests that sensor fusion and stealth remain very important and collaboration with drones is key, while traditional characteristics such as speed and maneuverability have declined in relevance.
In fact, industry has not really come to a conclusion about what a sixth-generation fighter might be. Its approach privileges revolutionary thinking at the expense of the incremental innovation that has always been part of aircraft design and production.
That is why some in the community are now inclined to argue that the “generations” frame has become more of a constraint—and even an illusion—than a useful heuristic.
The Fighter Categorization Challenge
Categorization is one of the most natural cognitive habits. Categorizing fighter jets by some generational scheme thus reflects a basically inevitable human trait. That doesn’t mean the generational classification is above criticism.
Perhaps instead of obsessing about fielding the “next generation” of fighter, we should instead engage in a careful analysis of which technologies and platforms are needed to meet the ends airpower is meant to accomplish.
About the Author: Dr. Robert Farley, University of Kentucky
Dr. Robert Farley has taught security and diplomacy courses at the Patterson School since 2005. He received his BS from the University of Oregon in 1997, and his Ph. D. from the University of Washington in 2004. Dr. Farley is the author of Grounded: The Case for Abolishing the United States Air Force (University Press of Kentucky, 2014), the Battleship Book (Wildside, 2016), Patents for Power: Intellectual Property Law and the Diffusion of Military Technology (University of Chicago, 2020), and most recently Waging War with Gold: National Security and the Finance Domain Across the Ages (Lynne Rienner, 2023). He has contributed extensively to a number of journals and magazines, including the National Interest, the Diplomat: APAC, World Politics Review, and the American Prospect. Dr. Farley is also a founder and senior editor of Lawyers, Guns and Money.
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