While 5th and 6th-Gen fighters grab headlines, the backbone of global air power broadly remains firmly rooted in 4th-Gen platforms – and for good reason. Cost, payload capacity, and operational flexibility keep these enduring fighters relevant.
Peer-on-peer warfare is back. The spectre of superpower confrontation and war via proxies has been almost fully exhumed from its Cold War grave by the Russian ‘Special Military Operation’ in Ukraine, and, seemingly, by the encouragement it has given to other nations and groups in and around the world’s flashpoints. The Chinese desire to ‘reunite’ with its ‘rogue province’, Taiwan, continues to burn brightly and likely acts as – despite the conflict in Ukraine – the pacing concern for planners and commanders in the Pentagon. More recently, the ever-febrile Middle East continues to boil over, with Israel’s continued direct operations against Hamas in Gaza, while Iranian procrastination over inspections of its suspected nuclear weapons programme has provoked ire of the US, as has its support for the Houthis in Yemen. Most recently, the decades-long simmering tensions between India and Pakistan over the disputed Kashmir region, with the flashpoint being an attack by Islamic militants on 22 April 2025, has triggered serious clashes between the militaries of both nations.
Russia and Ukraine continue to operate 4/4.5-Gen fighters in their full-blown war, while Israel has struck targets in Lebanon, Gaza, Yemen and even Iran with their mixed 4/5-Gen fighter fleet, and the US have been very publicly hitting the Houthis with tactical aircraft and stand-off weapons. Perhaps the highest profile aspect of the recent Indo-Pakistan clash has been the use of 4th-Gen fighters. Although so close to the events at time of writing, it is perhaps sensible not to believe on sight all media reports and briefings (from both sides); nonetheless, there does seem to be consistency in the accounts that a prolonged beyond visual range (BVR) missile battle was fought between Pakistani and Indian fighters, with, it seems, losses on at least the Indian side. Indeed, shares in the Chinese manufacturer of the Pakistani Air Force’s J-10C ‘Vigorous Dragon’ fighters, CAC, have it seems risen over 20% since the clashes.
Talking about my generation
However, before investigating further, it may be worth clarifying what the term ‘4th-Gen fighter’ actually means. The concept of jet fighter ‘generations’ was largely invented by journalists to help distinguish between different eras of fighter aircraft, before being employed by fighter manufacturer salesmen as a convenient tool to help persuade sceptical politicians that they really needed to invest in new platforms to prevent being left behind by potential opponents. No such equivalent exists, for example, in the helicopter world. Recently, in NATO studies surrounding the development of next-generation rotorcraft (NGR), the nomenclature of ‘legacy’, ‘enduring’ and ‘next-generation’ have been adopted. In this lexicon, 4thGen would be considered ‘enduring’ – and the category would also cover the awkwardly shoe-horned ‘4.5-Gen’ used to distinguish both more recent platform designs, such as the Rafale and Eurofighter Typhoon, but also the upgraded versions of ‘early’ 4th-Gen platforms such as the latest Block F-16s, F/A-18E/F Super Hornet, various Su-30/35 upgrades and, most recently, the F-15EX (which some are dubbing ‘Gen 4++’). ‘Legacy’ would incorporate those remaining MiG-21/23, Su-22, Jaguars and F-4 Phantoms inter alia that are still to be found in the order of battle (ORBAT) for some nations.
Importantly, the concept of ‘generations’ is not about platform design age or era, but about attributes. Hence why 1970s core designs such as the F-15 and F-16 can still be genuinely considered ‘4.5-Gen’ as their digital backbones, sensors, weapons and situational awareness capability are all of the very latest standard. However, they will never reach the attributes required to be considered truly ‘5th-Gen’ as they are not inherently low observable (LO), don’t feature the ‘hyper agility’ found in most 5th-Gen platforms such as the F-22, and cannot routinely supercruise (conduct prolonged flight in excess of Mach 1 without the use of reheat). 5th-Gen was specifically designed to dominate 4/4.5-Gen in air combat terms – the ability to see first, shoot first was enshrined into the attributes, with 5th-Gen platforms making good use of their LO features (especially the head sector), infrared search/track (IRST) and secure low probability of detection (LPD) datalinks to detect opponents passively and then pass threat and tactical information between elements, and receive directions from the ‘Battle Captains’; the ‘big idea’ is that at the initial tactical presentation, 5th-Gen aircraft place themselves in the optimum position for launching their own BVR missiles while minimising the chances of being shot back. Air combat has never been about fairness, after all.
All of which might leave one with the impression that the days of the 4/4.5-Gen fighter are nearing their end – especially with several 6th-Gen platforms already deep into their development cycle. Indeed, the US Air Force (USAF) has recently confirmed that ‘risk reduction’ work using Defense Advanced Research Projects Agency (DARPA) ‘X-Planes’ from both Lockheed Martin and the eventual winner, Boeing, have been flying for some five years, logging hundreds of flight hours in total secrecy, maturing the technologies required for the F-47 Next Generation Air Dominance (NGAD) programme. When considered alongside the US Navy’s FA-XX programme, the Franco-German-Spanish Système de Combat Aérien du Futur (SCAF) and the Tri-Nation (UK, Italy, Japan) Global Combat Air Programme (GCAP), as well as Chinese programmes such as the J-36, it’s understandable to think that pitching more 4/4.5-Gen fighters to the world’s militaries is going to be a hard sell. Except, increasingly, it’s not.
Only two 5th-Gen aircraft have made it to full production in the West – the F-22 and F-35. In Russia, the Su-57 ‘Felon’ has only been produced in vanishingly small numbers (with some commentators sceptical that it should even be considered a 5th-Gen design). China has fared much better, with the J-20 ‘Mighty Dragon’ now in service in appreciable numbers (circa 300), with the J-35 in the Operational Testing phase.
However, with the exception of the F-35 programme, which by early 2025 had exceeded the 1,100 aircraft delivery mark, most 5th-Gen fighters have only been produced in relatively small numbers. The USAF originally anticipated buying over 700 Raptors to replace its F-15C Eagle in the air superiority mission, but post-Cold War reductions in spending, coupled with high development and production costs (not helped by the US Congress effectively banning any export sales…) reduced those numbers to 381 and, eventually, just 187 combat-coded aircraft (plus eight test and trials aircraft). It’s a far cry from the 4,500+ F16s, 2,400 F-15s, 1,500 ‘classic’ F/A-18s, and 600+ Eurofighter Typhoons that have been produced by the West alone. In Russia, over 1,500 ‘Flanker’ variants (Su-27, Su-30 and Su-35) have been built, with a similar number of MiG-29s.
The enduring relevance of 4th-Gen
F-35 aside, the vast majority of Combat Air Mass, globally, still consists of ‘enduring’ Gen 4/4.5-Gen – and it’s likely to remain so for some time yet. Why?
The obvious first reason is cost. The development and production costs for 5/6-Gen platforms are, by comparison, much steeper than their 4/4.5-Gen forebears. Those precious attributes of LO, supercruise, hyper-agility and sensor fusion are all ‘high ticket’ items. LO design is complex, and the materials required are invariably exotic and expensive. Design tolerances are extraordinarily tight, which flows down to the manufacturing process. The additional costs of the ‘5th-Gen Privilege’ are added at every stage of the process. An example of the sometimes competing tensions between LO needs and production design is the requirements for supercruise. Designers face significant challenges in ensuring the powerful engines required receive their airflow in sufficient quantity and at an acceptable speed (throughout a very broad and rapidly changeable manoeuvre envelope), while also attempting to make the intakes and ‘front end’ of the engine, traditionally very large radar signature aspects, either shrouded or hidden. Fitting the platform with distributed sensors, LPD radios and Tactical Data Links and fused tactical information to the pilot all come at high cost.
Even the F-35, which currently anticipates a programme of record comfortably in excess of 3,000 aircraft (the USAF alone expect to purchase nearly 2,500), has suffered from controversies over its costs – especially the most complex VSTOL F-35B version. The F-35 is only deemed as ‘affordable’ because, firstly, the DoD ‘dialled down’ some of the complexity of the F-22’s requirements and, secondly, Congress realised that their draconian restriction on blocking the export of F-22 had somewhat backfired; Australia, Japan and Israel had all expressed an interest in buying batches of the aircraft, which would have kept the production line going after 2012 and resulted in an ‘F-22 Community’ to help share future upgrade costs. The broad F-35 coalition (19 countries and counting) will support the US to defray some of these downstream upgrade costs, while, for other nations, ‘buying in’ to the production phase of the programme ensures they are spared much of the non-recurring expenditure (NRE) consumed by the aircraft’s initial design.
It’s also not just acquisition costs that are high for 5th-Gen (and likely 6th-Gen) aircraft. Day-to-day maintenance of an LO aircraft is more expensive than an equivalent 4/4.5-Gen platform. Care has to be taken over paint finishes for example. ‘Stealth’ is a finely balanced attribute, and an individual platform’s signature can be degraded by even minor imperfections in husbandry – which is particularly problematic in maritime environments. Carrier Ops are probably the most demanding environmental conditions for tactical aircraft to operate in – demanding extra robustness in the design to cope with the stresses of catapult launches and ‘traps’, not to mention the salt air/water environment. It is, perhaps, one of the reasons why the US Navy has been so keen to keep the Super Hornet in production alongside the F-35B and F-35C.
For the F-22, there is the additional factor of the small fleet size resulting in concomitant support costs. Most open sources place the cost-per-flight hour of a Raptor at somewhere between USD 70,000–85,000, compared to the F-15C/E at circa USD 40,000. By comparison, one of the design drivers for the F-15EX is to reduce that figure to circa USD 30,000 per hour. Clearly, when quoting operating costs, there are a lot of factors to be considered – including all the support elements, not just the fuel and spares. Yet a small-size fleet simply doesn’t have the numbers of airframes to amortise those fixed support costs as efficiently as a large fleet does.
The LO attribute also provides other limitations on 5th-Gen employability, further making the case for retaining a balanced fleet between generations.
First, payload. One of the simplest ways to lower signature is to mount weapons internally in bays; external pylons, and the weapons themselves, are distinctly ‘non-stealthy’, as well as increasing the aircraft’s drag index with knock-on effects on speed (drag and stores carriage clearance limits) and fuel burn, reducing both range and endurance. However, there is only so much space inside an aircraft for essential systems and consumables – especially fuel. Weapons bays take up a lot of room, are mechanically complex and require significant design work to ensure that the required weapons fit can be connected to the stores management system (SMS) and that weapons can be deployed into (potentially supersonic) airflow without risk to the launch aircraft. Additionally, simply opening a weapons bay has a significant impact on the aircraft’s radar signature – therefore the sequence of doors opening, weapon release, doors closing has to be as rapid as possible. There is also the added complication of passing target data to an internal weapon. Not too hard for a GPS guided munition or an air-to-air Missile (AAM), such as the AIM-120 AMRAAM, which is receiving data from the aircraft’s systems, but it is potentially a problem for an infra-red AAM (IR AAM) which, traditionally requires a ‘lock-on before launch’ (LOBL), with the seeker head finding the target before launching. Earlier generation IR AAMs, such as the AIM-9L Sidewinder, would not function from an internal weapons bay. As a result, the US has developed the AIM-9X Block II which has a datalink to permit ‘lock-on after lunch’ (LOAL) from an internal weapons bay, with the missile being cued by a helmet-mounted display and cueing System (HMDCS), enabling high ‘off boresight’ engagements. However, the similar, UK-designed ASRAAM is only cleared for external carry on the F-35.
For the F-35, unless it is configured in ‘Beast Mode’ with a full set of external pylons (effectively destroying its LO signature and reducing speed/range/manoeuvrability), like all 5th-Gen platforms, the issue becomes one of magazine size. As a graphic example, the F-35A, as standard, carries just four AIM-120 AMRAAM internally – though the ‘Sidekick’ door modification enables it to carry six. However, the F-15EX has demonstrated an ability to carry no fewer than 12 AMRAAMs, with the potential to carry up to 22 AAMs (a mix of AMRAAM/AIM-9X) if the AMBER (Advanced Missile and Bomb Ejector Rack) is fully developed.
This relative payload weakness transfers to the air-to-ground role as well – with 5th-Gen aircraft in LO mode struggling to carry the combat payload of their 4/4.5-Gen predecessors. It’s not just number of stores either. There is a physical limit to the size of a weapon that can be accommodated internally. The F-35A/C can carry a 907 kg (2,000 lb)-sized weapon internally, but the lift fan in the F-35B reduces the size of the weapons bay such that only 454 kg (1,000 lb)-sized bombs can be carried – and it also cannot employ the ‘Sidekick’ modification. The US Navy has also just acknowledged the existence and entry into service of the AIM-174B ‘Gunslinger’ very long-range AAM. It is based on the standard US Navy ship-based missile, the SM-2, and is five times the launch mass of the AMRAAM, weighing in at nearly 900 kg. It appears to be too big for the bays of the F-35, but its range, estimated in excess of 278 km (150 NM), make it a replacement for the long-missed AIM-54 Phoenix for the task of ‘splashing’ anti-ship missile (ASM) carrying bombers before they reach their launch points.
Therefore, one of the reasons that 4/4.5-Gen fighters will endure, and continue to grow new capabilities such as AIM-174B and AMBER, is that their designs enable rapid adoption of new weapons and the ability to carry a lot of them by comparison. In a peer engagement, the probability of kill (Pk) of even the best AAMs will be reduced by an opponent’s tactics and countermeasures – therefore magazines will need to be deep, and that’s simply not a 5th-Gen attribute if attempting to stay LO.
The synergy between a mixed force of 5th-Gen and 4/4.5-Gen is evident. In the UK, the RAF considers the F-35B to be the ‘assassin’ and the Typhoon the ‘thug’. The former goes far ‘up threat’ exploiting its LO characteristics to survive, finding targets air and ground, for the Typhoon missile/bomb trucks to prosecute. While ‘up threat’, the ‘assassin’ can, of course, both provide threat warning to the Typhoons and swiftly ‘snipe’ any obvious threats to itself, or, if carrying a mixed weapons load, strike a fleeting high-value target (HVT) if one presents itself.
Finally, there’s the matter of training. 5th-Gen (and to be assumed 6th-Gen) designs rely heavily on their signature and tactics, techniques and procedures (TTPs) to be successful. In day-to-day flying, LO aircraft often fly with Luneburg lenses fitted to increase their radar signature. These have a dual purpose; first, the aircraft is easier to detect on military and civil radars, and second, they mask the aircraft’s actual signature from those trying to measure it. This means it’s very difficult for crews to fly deeply realistic training missions without revealing key aspects of signature and TTPs. Inevitably, this leads to a heavy reliance of synthetic environments – but pilots join to fly, not to simulate flying in the virtual world. Real flying is important for moral and physiological reasons – ‘g fitness’ is perishable. In this sphere, there are far fewer restrictions on 4th-Gen platforms. It’s also not just pilots who need training – ground and maritime specialisations need real jets turning up on their exercise for their own training. The solution might be to acquire a ‘surrogate’ jet, likely an advanced training aircraft with some combat capacity, but they will never be able to match the ‘punch’ of a 4th-Gen aircraft.
A glance toward the future
The 5th-Gen lack of magazine size seems to be addressed by the 6th-Gen designs currently taking shape. All appear to have significantly larger airframes than 4/5-Gen aircraft. Some of the extra space is clearly fuel, as ranges under discussion are twice that of ‘enduring’ platforms, but it will also increase the area available for weapon stowage. With one eye on the future, the larger size will also be required for energy storage when directed energy weapons (DEWs) become available. The 6th-Gen attributes appear to be range, LO, deep magazines, the use of artificial intelligence (AI), unmanned collaborative combat aircraft (CCA), the potential for variable cycle engines to push towards hypersonic speeds and the ability to exploit DEWs.
Quite a shopping list, and not a cheap one. In air combat, as in much of warfare, ‘quantity has a quality all of its own’. The vulnerability of aircraft carriers and fixed air bases has often been brought into question. The prospect of having an expensive, small, ‘silver bullet’ force of ‘assassins’ effectively grounded by the destruction of their airfield facilities or floating base is a headache for military planners.
4th-Gen aircraft, many of which are Cold War-era designs, have austere operating ‘baked in’ and can be rapidly ‘turned’ between sorties. These 4th-Gen ‘thugs’ are tough, cheap to buy and fly by comparison to 5/6-Gen, readily adaptable, available in large numbers, still in production, and carry plenty of firepower into the fight. The sales success of F-15EX, Typhoon tranche 4, F-16 Block 70/72, SU-35, and the J-10 shows that the day of the 4th-Gen fighter isn’t over. Indeed, their capabilities and numbers continue to grow.
Author: Paul ‘Foo’ Kennard is a former UK RAF Helicopter pilot, Tactics & Electronic Warfare Instructor and Operational Evaluation pilot. He has seen operational service in Northern Ireland, Bosnia, Kosovo, Iraq and Afghanistan. He now runs his own independent consultancy company, Ascalon, providing specialist technical and user input into a wide variety of defence & aerospace programmes for governments, NATO and the broader defence industry; and operates as a freelance journalist.
