Overall, the Vietnam analogy highlights potential vulnerabilities of the F-35, but also cannot definitively account for the different technologies in play when evaluating the Lightning’s adaptability to the air superiority role. Key performance parameters concerning the effective range of long-range IRST, radars and missiles used by and against an stealth jet are probably necessary for a fairer evaluation, but are likely to be kept under wraps by anybody in a position to know.

Conventional wisdom can offer contradictory insights. Are we doomed to forget the past, and thus condemned to repeat it? Or are we always preparing to fight the last war while failing to think ahead about how the next one will be fought?

From the standpoint of military strategy, it is at once important to learn from operational experience, without blindly assuming that future conflicts will playout in the same fashion. This brings us to the controversial, thousands of which are set to enter wide-scale service in the three warfighting branches of the U.S. military and at least nine other countries.

(This first appeared several months ago.)

Oriented as a multirole platform, the F-35 is slower and less maneuverable than preceding fourth-generation fighters it will eventually replace, or the air-superiority oriented F-22 Raptor stealth fighter. While more focused as an air-to-ground platform, the Lightning is intended to defeat more agile opposing fighters by detecting and engaging them beyond visual range (BVR) with air-to-air missiles, while hopefully avoiding a within-visual range (WVR) dogfight where it may be detected and out-maneuvered.

However, to some critics this sounds worrisomely similar to how the U.S. military envisioned its F-4 Phantom performing in the Vietnam War. The comparison so natural that you can also check out an earlier article on this by my colleague Michael Peck.

The F-4 Phantom (profiled in greater detail in this article) was a huge beast of a plane with two powerful J79 turbojet engines that could propel it up to two times the speed of sound, and a then-powerful radar housed in its nose. The Phantom was armed with new medium-range AIM-7D and E Sparrow medium-range missiles, as well as short-range AIM-9 Sidewinders AIM-4D Falcon heat-seekers.

The Air Force expected the Phantom would detect aerial adversaries from dozens of miles away, swoop down towards them at supersonic speeds and take out its foes with Sparrow missiles from up to twenty-eight miles away. Short-range dogfights were simply not intended or trained for, as the Phantom was not a particularly maneuverable bird.

Needless to say, this was not how things played out when U.S. fighters encountered North Vietnamese MiG-17 and MiG-21 jets over Vietnam. Though the much lighter MiG-21 had only a weak radar, its pilots were guided to intercept American raids by ground controllers, per Soviet doctrine. Also, American rules of engagement forbade opening fire until enemy aircraft had been positively identified—usually within visual range.

When the U.S. fighters finally did get a chance to open fire, the faulty Falcon and Sparrow missiles achieved kill probabilities below 10 percent. The shorter-range Sidewinders were somewhat more effective with 15 percent kill rates, but getting into an advantageous position to launch the heat-seekers often involved getting into knife-fighting range with the nimble MiGs. The kill-loss ratio of the more expensive U.S. jet fighters in general fell as low as 2:1 in certain phases of the Vietnam War.

Over time, the U.S. Air Force and Navy adjusted by fielding improved Sparrows and Sidewinder missiles, and retiring the older AIM-4 Falcon. Later, cannon-armed F-4E Phantoms were deployed, giving pilots a backup weapon in close range fights. Meanwhile, the Navy responded by forming the Top Gun school to teach naval aviators short-range dogfighting skills—lessons which resulted in the Navy Phantom pilots scoring a superior kill-ratio.

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Ultimately, designers of the new generation of F-15 and F-16 fighters made sure to incorporate cannon armament and excellent maneuverability, as well as high speed and advanced avionics in the Phantom’s successors.

While today’s F-35 is intended to operate using long-range missiles and powerful radar, it trades the Phantom’s speed (the Lightning is considerably slower, with a maximum speed of Mach 1.6 to 1.8) for a reduced radar cross section that will make it very difficult to detect and engage with long range sensors and weapons. Thus, while the Air Force concedes the F-35 is at a disadvantage in a close encounter with say an Su-35, in theory it should detect that Su-35 from further away, launch missiles at it from dozens of miles away, and then hi-tail it.

So how can we judge whether the air battles of the future will play out similarly or differently the skirmishes fought over Vietnam?

Just How Likely Are Beyond-Visual Range Missiles to Hit a Fighter?

Air-to-air missiles have improved enormously since their first wide-scale employment during the Vietnam War. It doesn’t follow then that today’s AIM-120D, Meteor or R-77 BVR missiles will perform as poorly as the AIM-7E did in the past.

However, while testing of modern BVR missiles suggests a decent hit rate (around 50 percent is a common estimate) this was also true of preceding aerial missiles. More importantly, despite the increasingly long range of new BVR missiles, the vast majority of air-to-air shootdowns since 1970 have continued to be performed within visual range using both short- and medium-range missiles, as you can see in this detailed history. Many of the BVR hits that were scored in combat were against poorly equipped and trained adversaries that lacked radar-warning receivers to alert them of incoming attacks—unlikely to be true of a clash between modern near-peer opponents.

It is important to acknowledge then that the official maximum effective range of a missile is far greater than its practical effective range to guarantee a high probability of kill verses a fast and agile target. After all, a targeted fighter can simply race away from an incoming missile launched from beyond its “no-escape zone.” So, while the AIM-120D has a nominal range of 110 miles, an F-35 would have to stalk closer to enemies to ensure a good probability of a kill. This bring us to an important follow up question.

Just how close can a stealth fighter approach before it gets detected?

Stealth fighters are not actually invisible after all—just difficult to detect. The question remains just how close they can approach an enemy before they show up on their sensors.

To begin with, many modern fighters boast long-range Infrared Red Search and Track Systems, as well as electro-opitcal sensors, with effective ranges of up to fifty or one hundred miles. Of course, designers have done their best to reduce the heat signature of stealth aircraft, but only so much can be done to mask the incredible heat generated by jet engines. On the other hand, heat-seeking missiles are generally much shorter in range. Nonetheless, infrared surely constitutes an Achilles heel of the stealth fighters.

Another gambit for hunting stealth aircraft is to use low-bandwidth radars, which are capable of plotting the general position of a stealth fighter, though they lack the precision to target them with guided weapons. A ground-based low-bandwidth radar could detect the presence of a stealth jet and direct a flight of high-speed fighters to close in on its general vicinity until they detect the fighter with its IRST, or even X-band targeting radars at shorter ranges.

In this scenario, a stealth jet would still likely get to fire first at such fourth-generation interceptors, though it could be overwhelmed by numerically superior attackers. Disengaging could prove risky as well due to the F-35 being slower than most fourth-generation jets. On the other hand, it will have an easier time slipping out of radar range.

How much does dogfighting matter in an age of short-range High-Off Boresight missiles?

According to U.S. military doctrine, energy (speed, and altitude that can be traded for speed) is more important than maneuverability. A fighter in a high-energy state can dictate the terms of the battle by engaging or disengage from adversaries when it pleases, and outrun incoming missiles. On the other hand, while tight maneuvers may help avoid an incoming missile, they drain away energy, leaving an aircraft a sitting duck for a follow-up attack.

Furthermore, some argue that short-range weapons have become so lethal that dogfighting agility simply won’t matter very much in the event of a ‘merge’ between opposing fighters. This is because of two related new technologies: Helmeted Mounted Sights, which allows a pilot to target enemy aircraft simply by pointing his helmet at any enemy airplane; and highly maneuverable High Off-Boresight (HOBS) missiles which can engage adversaries even when the launching platform is not pointing at them.

First fielded by Russia and later adopted by the United States in the form of the AIM-9X missile, these technologies mean that it is not as necessary for a fighter to out maneuver its opponents to launch effective weapons at them. To be fair, however, a fighter which is pointing at its target will still impart more of its velocity to any missiles launched, and thus increase the chance of a hit.

Nonetheless, modern short-range missiles are generally estimated to have a hit probability of 80% to 90% for WVR engagements—suggesting that two similarly equipped aircraft aware of each other’s presence would likely destroy each other. To avoid such an outcome, fighter pilots in the future may well prefer to sling missiles from long-range and try to stalk their opponents undetected, rather than close for an aerial knife fight.

Will Rules of Engagement Constrain Fighters to Short-Range Engagements?

The circumstances which forced Phantom pilots over Vietnam to largely forsake taking advantage of their BVR-capable missiles may seem specific to that conflict—but in reality, rules of engagement heavily favoring visual contact with the enemy have remained the rule rather than the exception.

This is both because nobody wants to accidentally shoot down an airliner, but also because opposing fighter jets have often engaged each other in ambiguous circumstances short of total war where the authorization to engage may not be given until the aircraft are relatively close to each other. Think, for example, the downing of a Syrian Su-22 in 2017 by a U.S. Navy FA-18 Super Hornet or two aerial skirmishes involving F-14 Tomcats and Libyan Su-22s and MiG-23s in 1981 and 1989.

Under these circumstances, an F-35 patrolling, say, a no-fly zone might have to approach closer to a hostile aircraft and expose itself to detection and sacrifice its stealth advantage. A faster and more maneuverable fourth-generation jet like an F-15 or Rafale would seem preferable in such a scenario. Of course, that limitation could be solved simply by employing older fourth-generation jets for such air superiority roles, while reserving the F-35s for the deep-penetrating strike roles and intelligence-gathering roles they are optimized for.

Overall, the Vietnam analogy highlights potential vulnerabilities of the F-35, but also cannot definitively account for the different technologies in play when evaluating the Lightning’s adaptability to the air superiority role. Key performance parameters concerning the effective range of long-range IRST, radars and missiles used by and against an stealth jet are probably necessary for a fairer evaluation, but are likely to be kept under wraps by anybody in a position to know.

Sébastien Roblin holds a master’s degree in conflict resolution from Georgetown University and served as a university instructor for the Peace Corps in China. He has also worked in education, editing and refugee resettlement in France and the United States. He currently writes on security and military history for War Is Boring.