Fighter jets have for decades been classified by generation, currently from the first generation which began in the late 1940s to fifth generation which saw its first aircraft inducted into service in 2005, with each generation corresponding with certain technologies used by the airplane. Each consecutive generation has fielded cutting edge systems designed to give parties an edge in combat over their predecessors, and with the jet age dominated by superpower confrontation between the Untied States and the Soviet Union the two were always at the cutting edge of combat aircraft technology. While jets of the first generation most prolifically went head to head over the Korean Peninsula during the Korean War, the second and third generations would come to be synonymous primarily with the Vietnam War and the Arab-Israeli wars. The fourth generation, first entering service in 1974 with the U.S. Navy’s commissioning of the F-14 Tomcat, saw extensive service in all Western military interventions since and remains the mainstay of the aerial warfare capabilities of all modern aerial powers today. The fifth generation, which came into service with the U.S. F-22 Raptor and introduced advanced stealth technologies, has since become the latest level of accomplishment of military aviation - with China, a new but fast progressing player in the arms race, and Russia, inducting their own fifth generation fighters in 2017 and 2018 respectively.
While each fighter is assigned a generation, the inter generational boundaries have often been somewhat flexible - which has meant that a number of fighter designs once sufficiently upgraded can effectively jump a generation, sometimes two, as new technologies are integrated onto older airframe designs to vastly enhance their performance. A key example of this is the U.S. F-5 Freedom Fighter, a second generation fighter which entered service in 1962 and was widely exported to American allies at the time of the Vietnam War. The aircraft’s low maintenance and operational costs, its flexibility and its reliability led it to become a highly prized asset - one which would be extensively modernised with third generation technologies to enter service as the F-5E Tiger II in 1972. The aircraft incorporated new and more powerful twin General Electric J85-GE-21B turbojet engines, a higher fuel capacity, longer range, greater wing area, improved better turn rate, new air to air munitions and an Emerson Electric AN/APQ-159 radar and the option for aerial refuelling. This made the F-5E one of the most capable third generation jets in service, considerably more capable than most third generation jets of a similar weight. Seeing more potential in the highly versatile F-5 airframe, the fighter would later see further modernisations which would lead to its emergence as a fourth generation jet. While the U.S. Navy based the F-18A fourth generation fighter heavily on the F-5, and did not develop the Tiger II further for export due to the emergence of an effective replacement, Iran, Thailand, Switzerland, Singapore and Taiwan would all extensively modernise their F-5E jets. These jets would by the 21st century come to surpass the capabilities of the early F-18A and F-16A fourth generation light fighters, incorporating cutting edge avionics, beyond visual range mutinous such as the AIM-120, and radar systems. Indeed, the Swiss Air Force has expressed a preference for its modernised F-5 jets over the F-16C due to the former’s lower maintenance needs and their highly similar combat capabilities. The F-5 in this way can, with the integration of new technologies over five decades, be said to have jumped not one but two generations in its capabilities and its sophistication. Other fighters such as the Chinese J-7 have also been known to jump two generations, with the J-7G today serving as a highly capable fourth generation light platform similar to the F-5.
While the narrow definition adopted for fifth generation fighters requiring purpose built stealth airframes has restricted advanced combat aircraft which lack such capabilities to be termed ”˜4+’ or ”˜4++’, the Russian MiG-35 and Chinese J-11D being key examples, not only is there considerable mobility between the second, third and fourth generations, but mobility between the fifth and sixth generations may well also be possible. While the precise definition of a sixth generation fighter has yet to be made, it is likely not to restrict the shape of a fighter’s airframe but rather to require a number of advanced next generation technologies to be integrated, including energy weapons, hypersonic missiles and superior electronic warfare and radar evading capabilities among others. The Russian Su-57 for its part had been designed from the outset with the intention of developing a sixth generation fighter, with early production variants of the aircraft set to be inducted in limited numbers by the Russian Air Force as fifth generation fighters while the design will only enter full production when sixth generation technologies can be integrated. While the U.S. F-22 is restricted in its potential for modernisation, and efforts put into modernising the fighter have been highly limited in their success, the U.S. F-35 fifth generation light fighter and the Chinese J-20 and J-31 fifth generation fighters could all potentially see service as vastly upgraded sixth generation jets in years to come. With China already heavily invested in researching cutting edge new technologies, from laser weapons to stealth systems and increasingly fast and far reaching ramjet power missiles for its existing fighters, modernisation of fifth generation designs to the sixth generation platform remains a possibility.
The F-35 for its part, with the program set to cost over $1.6 trillion and hundreds of billions already sunk into research and development, may well also follow the example of its predecessor the F-5, with late production variants gaining sixth generation capabilities - possibly under the designation F-35E. Such fighters would be key to supporting the heavier air superiority fighters, purposely designed with sixth generation capabilities to replace the F-22 Raptor under the F-X Air Dominance Initiative, with heavily upgraded F-35 jets serving as a lighter, less costly and more numerous complementary platform. Considering the immense projected cost of developing and fielding sixth generation fighters, there is a considerable chance that the mainstay of major powers’ sixth generation fighter fleets in the early years of the new generation will be comprised of heavily upgraded airframes which date back to the fifth generation - much as the airframes of fourth generation F-5s date back to the second. This does not necessarily mean that these fighters will be less capable than purpose build sixth generation jets, with the F-5E Tiger II’s superiority over several third generation designs strongly indicating otherwise, but rather serves as a more cost effective means for major powers to begin to build up sixth generation air fleets as new technologies are developed.