Infrared Search And Track Systems And The Future Of The US Fighter Force | World Defense

Infrared Search And Track Systems And The Future Of The US Fighter Force


Nov 19, 2017
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3/26/15 3:10pm
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Illustration for article titled Infrared Search And Track Systems And The Future Of The US Fighter Force

Lockheed has a new modular sensor system for combat aircraft dubbed the "Legion Pod" that aims at plugging a major hole in US air warfare capability. It provides a bolt-on Infrared Search and Track (IRST) system for optically hunting down enemy aircraft, especially stealthy ones, that our radars have trouble detecting.


The Legion Pod is pitched as a plug-and-play system that can be rapidly adapted to suit different aircraft and customers needs. Presumably, different sensors could end up being carried in the 18 inch thick pod system, not just the IRST and the data-link alone that the pod was unveiled with. Still, even as an IRST alone, it and other systems like it, may be absolutely essential when it comes to retaining America's air supremacy edge in what is quickly becoming an increasingly uncertain age of air combat.
The USAF, Navy and Marines, should be funded to field the pod en masse after its capability is verified, as the Pentagon is living in denial of its aging and very prevalent 4th generation fighter force's ability to remain relevant over the battlefields of tomorrow. At the very least, we need to train our fighter forces to counter this capability as threats that are prevalent throughout the world have been fielding similar IRST systems for decades, with newer systems being much more capable than their predecessors. We can do this by supplying our aggressor squadrons with an IRST capability, and the bolt-on Legion Pod is the best answer we've yet seen to answer this problem.
Blurry Past, Sharp Future:
At its most basic level, an Infrared Search and Track system is an infrared energy detection device that is usually fitted in a spherical glass enclosure on the front of a fighter aircraft. The systems scans the airspace ahead of the jet for heat signatures caused by aircraft engines and/or skin friction caused by the aircraft flying through the air. Once the system detects a target, it usually has an ability to lock that target up, or a way to facilitate the crew in slaving their fighter's radar onto the point in space where that heat signature exists in order to attempt a radar lock. Modern variations of IRSTs can search out to intermediate ranges, track multiple targets and even engage other aircraft using its telemetry data alone.
Infrared Search And Track systems were commonplace, although questionably effective, on American fighters during the 1960s and 1970s, and saw widespread use on Russian fighters from the late 1970s on. The Sukhoi Su-27 Flanker series and MiG-29 Fulcrum series of fighters have all been fielded with an IRST 'ball' just below their windscreens.
The capability of the IRST systems initially fielded on these Russian fighters is also suspect, but it is fairly well known that with the last two decades pr worth of advances in imaging technology and computer processing power, the IRST seems to have finally come of age.

Today, western fighter aircraft, namely the 'Eurocanard' series, all feature advanced IRSTs. These include the SAAB Gripen with its Skyward-G IRST, the Eurofighter Typhoon with its capable PIRATE IRST, and Dassault's Rafale with its dual aperture Front Sector Optics system.
Often times these modern IRST systems also include laser range finding functions and the ability to display a default raw image of what the IRST has locked onto, although this function is usually only useful to the crew at intermediate ranges and below.
No American fighters feature a IRST system today. Lockheed's Legion Pod is actually designed around the highly evolved Infrared Search and Track 21 (IRST21) sensor that was evolved from the F-14D Tomcat's AN/AAS-42 IRST. On the Tomcat, this sensor was mounted beside the Television Camera System (TCS), below the nose of the aircraft. A newer version of the AN/AAS-42, nicknamed "Tiger Eyes," is currently installed on the latest export models of F-15 Strike Eagles (F-15SG, F-15K), being housed inside the left-hand intake pylon that carries the aircraft's targeting pod.
The Navy's F/A-18E/F Super Hornet community is also getting the latest version of this same IRST, but in its case the IRST21 sensor and processing gear is mounted in the front section of the Super Hornet's centerline external drop tank. Because that tank now costs big bucks with the IRST mounted in it, it is no longer considered expendable and will be a fixed part of the jet when it is carried. This configuration has had its detractors, but fielding an IRST anywhere on the Super Hornet, even on the tip of a drop tank, is better than nowhere. The Super Hornet's IRST is entering low rate production now and should gain initial operating capability in the fleet by about 2018.
IRSTs Change The Fighter Pilot's Playbook:
Modern Infrared Search and Track systems can search, track and target an enemy aircraft while having a better ability to differentiate discreet aircraft in formations and intermediate ranges than many traditional fighter radar systems fielded today. They are also impervious to electronic warfare and jamming, a very big deal that we will discuss in a bit. Still, their biggest advantage is that they are a passive sensor, as in they work without emitting any electromagnetic energy at all.
The largest source of electromagnetic energy on any combat aircraft is from its on-board radar, which serves a similar function as an IRST when it comes to air-to-air combat. Just turning a fighter jet's radar can instantly give away the location, and at the very least, the fighter's presence. Enemy aircraft, ships and anti-aircraft ground installations have passive sensors that listen for, and are able to detect and classify, aircraft's radars' unique emission fingerprints. Even an aircraft's other, less powerful emissions, such as radio communications and some constant data-link emissions, can give away their presence to an enemy's sensitive electromagnetic 'listening' equipment.
With this in mind, the world of advanced IRSTs capable of detecting fighter sized aircraft at many dozens of miles away, even head-on, brings in a whole new world of tactics to the air combat arena. Prosecuting an air-to-air engagement with radar is like having a gun battle in a huge pitch-black warehouse with only flashlights to see. If both fighters are using their radars actively to search for one another it is like both people in said warehouse frantically looking around for each other with their flashlights on.
The guy (or gal) with the most powerful flashlight and the longest range, most powerful and accurate gun usually wins. Conversely, doing so passively is like leaving your light off and waiting for the other guy to turn on their light first. The problem is, that in the past, you still had to get a firing solution on the other guy somehow, and that usually involved turning on your radar (or your spotlight) at some point in time, or getting up so close to them that you could see them visually without your spotlight at all. This would be knife-fight territory, or in the air-to-air fighter world, infrared guided missile or even gun territory. Too close for comfort. Either way, it is not an ideal situation.
With an IRST equipped jet, you can bypass any passive electromagnetic detection by the bad guy (waiting for the other guy to turn on his radar or his 'spotlight') by having the ability to actively scan for an enemy's presence without emitting any electromagnetic energy at all (whether the enemy turns on their spotlight or not no longer matters as long as you are the one with an IRST, or your IRST has superior detection range). In other words, it is like ditching the spotlight and donning a pair of night vision goggles in that massive dark metaphorical warehouse.
With an IRST, there is no longer a need to wait for the other fighter to turn on their radar. While remaining electromagnetically silent, you can detect, track and engage him or her by detecting their physical infra-red signature without giving away your presence or location at all, even when it comes time to firing a shot at relatively long distances.

A tactic fighter crews can use, especially if their jet is equipped with a IRST, is one where they will turn off all of their emissions to remain undetected by the enemy's passive radar and radio sniffing sensors. In some cases, doing so could force enemy fighters, and even enemy ground radar installations, to turn on their radars in order to search for targets as they cannot sense any of them in the area passively. This can give the crew of the friendly fighter equipped with an IRST not just greater awareness about the presence of the enemy in their area, but it can also give them a direction to point their IRST system for focused scanning.
With modern digital Radar Warning Receivers (RWR) and Electronic Support Measures (ESM) installed on 4th and 5th generation fighters, not just the direction but also the distance, and thus the geolocation, of an enemy radar emission can be estimated with incredibly accurate results. This is done (roughly speaking) through measuring the angle of arrival of the enemy's radar's emissions and the time it takes those waves to hit different antennas spaced around the aircraft. This same information can also be collected by strategic assets over larger distances, such as by a RC-135 Rivet Joint, EP-3 Aries, U-2 Dragon Lady, or a E-3 Sentry to some degree, operating in the rear echelons of the battlespace. They listen for enemy emissions, and once they detect them and geolocate them, their locations can be forwarded to the electromagnetically silent friendly fighter via data-link that is set to receive only mode. That same enemy fighter's IRST can be set to cue on to the location where the enemy emissions are emanating from.

Once the fighter, still operating without broadcasting any electromagnetic emissions of its own, detects the enemy aircraft, either with the help of sensing its radar emissions or via scanning the sky with its IRST alone, it can start tracking it if it is within the IRST's range. Even if the enemy aircraft turns off its radar shortly after turning it on, that short broadcast may be all the friendly fighter needs in order to focus their IRST on the section of the sky that the enemy aircraft inhabits. Once the enemy aircraft is within a certain range, an advanced IRST, like the IRST-21 featured in the Legion Pod, can begin to provide weapons engagement quality targeting information for its crew to use.
Being able to provide a final firing solution and continued tracking, even at intermediate ranges, allows the friendly fighter carrying the IRST to fire on the enemy without ever turning on its radar, even for weapons launch. If jamming is used with this tactic, or the friendly fighter with the IRST is stealthy by design, or the enemy aircraft never turned on its radar due to fear of detection in the first place, instead relying on off-board radar guidance (Ground Control Interception) to hunt for targets, the enemy aircraft may never know the IRST toting fighter is hunting them down at all, yet alone firing a missile at them from dozens of miles away.

The last thing an enemy aircraft may hear is not the alarm of a being locked onto by a allied fighter's radar, but the radar warning alarm set off by the IRST toting friendly fighter's medium range air-to-air missile's active radar seeker turning on for its terminal phase of its attack (known as going "Pitbull" in fighter parlance). The missile would have flown most its flight via guidance from the IRST's telemetry that would have been periodically forwarded to the missile via data-link. Seeing as the missile would be traveling at around mach four, during the last dozen miles or so that it would use its own on-board radar for its terminal attack would amount to seconds of life left for the enemy fighter and its pilot. A horrifying warning of unexpected, pending death. Alternatively, if the missile used an imaging infrared seeker instead of a radar seeker, which some long range missiles in development may get, there would be no warning of the incoming missile at all.

IRST Equipped Fighters Plus Data-Links Equal Double Jeopardy For Enemy Aircraft:

If the battlespace that the friendly fighter with the IRST installed is fighting in is 'networked,' where a whole range of different assets (other fighters, AWACS, ground or surface radars and so on) are sharing a common sensor "picture" via data-link, that IRST equipped fighter could still maintain a synthetic radar "picture" of airspace around it while keeping its radar turned off. This would allow that fighter to retain an incredibly high state of situational awareness, while still remaining electromagnetically silent regardless of if the enemy turns on their radar at all.

For instance, an F-16 with a Legion Pod and a Link 16 data-link terminalinstalled could use an E-3 Sentry's radar picture to intercept an enemy fighter that is too afraid to turn on its own radar. Once in range of its IRST it can then prosecute the intercept and kill on its own, including a final weapons-grade firing solution. Basically, third-party sources are supplying the F-16 with the 'big picture' and once it is looking in the right direction it can use its IRST to shrink that picture down and enhance its targeting fidelity to a lethal level without giving away its own position via using its radar.
Currently, some advanced data-links, that are fairly platform and service specific, are exploring the ability to pass off engagement-grade sensor tracks of enemy aircraft, although this is uncommon fleet-wide. So although an F-16 may be able to see the general location of the bad guys via another aircraft's sensor picture, such as from an E-3 or an F-15C, and transmitted via data link, they are not precise enough for a final firing solution. The IRST gives that electromagnetically silent fighter the ability to create it own final link in the "kill chain" by creating a firing solution without using its radar.

Advanced data-links plus an IRST open up a whole new realm of tactical options for fighter crews. For instance, say a pair of F-16s equipped with Legion Pods were flying a counter air mission into enemy airspace along with a pair of F-15Cs. The two F-16s could push forward towards the enemy with all their radio emitting systems turned off, while the two Eagles lag behind dozens of miles but have their powerful radars on, actively scanning the airspace for well over 100 miles ahead. The 'silent' F-16s will still see the radar picture provided by the F-15Cs as that picture is transmitted in real-time via data-link. This means that the F-16s and their IRSTs can know exactly where the bad guys are and push toward those targets silently. Unless the enemy fighters turn on their own radars, and they have extreme range like the F-15's APG-63V3, which they most likely will not, the enemy only knows F-15Cs are in the area and filling the air with electromagnetic energy from their massive radars. The enemy may stay far enough away from those F-15s to remain outside of their weapons range, but for the F-16s flying in silent mode dozens of miles ahead of the F-15Cs are another story.
Once the electromagnetically silent F-16s are within range, they can create their own engagement quality target tracks without turning on their own radars, even guiding AIM-120 AMRAAMs onto their targets via their IRST's targeting information. By the time the missile's own radar activates, it is too late for the enemy, in seconds they would be destroyed by F-16s they never new were there, all the while thinking the F-15s were still well outside of their own AIM-120 AMRAAM's engagement range.
Now, let's replace those F-16s with a stealth aircraft equipped with an IRST and an sensitive radar warning receiver and electronic support measures suite. This combination can make the enemy's job of simply staying alive almost impossible based on known systems. Even if they were to turn on their own radars looking for aircraft between the radar emitting F-15Cs and themselves, they would not be able to see the stealthy jets, and in the process they would be giving the stealth fighters passive detection and targeting information via their radar emissions in addition to their IRST tacked heat signature.
Simply put, long-range active radar scanning with information forwarded via data-link to electromagnetically silent stealth aircraft sporting IRSTs is such a potent combo that the enemy has many ways to be shot out of the sky, but very few ways to live. Running really isn't even an option as you cannot run from something you have no idea is even there.

Ruining The Enemy's Jam Session:
The IRST may not be just an option, eventually it could become a necessity as electronic warfare, including jamming, hacking and pinpoint high-energy attacks from other enemy aircraft's powerful Active Electronically Scanned Array radars will make radar and traditional "omni-directional" data-links vulnerable to disruption. If big-picture data-links are not functional and radar is either too risky to use or too heavily impeded by electronic warfare attacks and jamming, the IRST is a fail-safe way to scan the skies for enemies and a way to subsequently avoid or engage them at medium ranges if need be. In other words, because an IRST uses infrared imaging to ply its searching, tracking and targeting trade, it is impervious to electronic warfare.
IRSTs can not only work well for US and allied nations combat aircraft, they can also work well for an enemy that has much less advanced fighter aircraft, but has upgraded those fighters with relatively cheap new subsystems. Electromagnetic silence, when paired with other aircraft using dissimilar tactics, such as active radar scanning, data-links and jamming, against a more advanced fighter force, can give that less advanced force a fighting chance at having a number of aircraft "break through" the more advanced enemy's fighter screen. If that same less advanced force were equipped with IRSTs, they could work more independently with a greater chance of survivability against a non-IRST equipped, but more advanced fighter aircraft.
The big risk here is that countries can take old and fairly crude fighter aircraft and bolt on some pretty wicked systems, at relatively low cost, to help level the air-to-air playing field.
The famous Cope India drills of that last decade saw US F-15Cs (albeit not equipped with the APG-63V1/2/3 AESA radar) getting surprised by old MiG-21s that had been upgraded to "Bison" standard and fitted with advanced Israeli-built self-escort jamming pods (EL/L8222).
When the Eagles were overwhelmed with more capable threats, such as India's Su-30MKIs, the MiG-21s, with their small radar and visual signature, high-off boresight heat seeking missile, helmet mounted sight and bolt on jamming pod, could sneak through into the F-15's inner sanctum, in some cases getting off an infrared missile 'face shot' before being killed or even merging with the F-15s for a turning fight.
Even though these diminutive MiGs gave America's famously capable air supremacy fighter a run for their money, they would have been much more deadly if they were equipped with an advanced IRST. This would have given them a totally passive beyond-visual-range engagement capability, while also enhancing their situational awareness and allowing them to stay electromagnetically silent. As a result, that possible short-range 'face shot' could turn into a medium range face shot, without the F-15s ever knowing they have been fired on until it was too late. Conversely, if the F-15Cs had an IRST, the MiG-21's small radar and visual signature, and its advanced jamming pod, would have had done little to help keep it from being detected.

Good Solutions Come In Podded Packages:
Active Electronically Scanned Array (AESA) radars have the ability to scan small areas of the sky very rapidly while jumping frequencies and limiting their power output. They are also less prone to jamming than their traditional mechanically scanned cousins. When running in low probability of intercept modes (LPI mode), it makes them hard to detect via enemy radar warning receivers and electronic support measures. In some ways, aircraft with such capable radar sets offset some of the utility of an IRST, but not anywhere near totally. Where IRSTs will be most useful in the future will be for detecting and engaging stealthy aircraft and cruise missiles.
Currently, much of the USAF, USN and all the USMC's fourth generation fighter fleet still pack mechanically scanned radar arrays which are far less likely to detect not just stealthy, but even small, low-flying targets like cruise missiles, than their new Active Electronically Scanned Array radar counterparts. Much of the F-15C fleet have these new AESA radars (APG-63V3) as do much of the Super Hornet fleet (APG-79), but this leaves hundreds of "legacy" F/A-18C/Ds and especially F-16C/Ds, the backbone of the USAF, without an independent way of detecting and engaging emerging threats until it it may be too late.

A large potion of the USAF highly adaptable F-16 fleet was going to get an AESA radar set as well as a structural upgrade, but like so many other things, this seemingly essential upgrade was cancelled due to lack of funding, which is largely caused by the floundering F-35 program and Sequester cuts. The Legion Pod could very well be a perfect interim capability for these jets that would give them sensitive new detection and targeting capabilities without having to buy a 'hard wired,' multi-million dollar AESA radar upgrade.

Alternatively, the USAF could buy AESA radars for half the F-16 fleet it plans to hold onto for the coming decades and Legion Pods for the other half, with each squadron fielding both capabilities equally. This would not only save money, but it would result in some exciting synergistic capabilities that would truly exceed the sum of their parts.
By leveraging data-links, a single division of four F-16s, two with AESA radars and two with Legion Pods and older APG-68 mechanically scanned array radars, could share information freely, thus one jet not having a legion pod could use their wingman's sensor data from their Legion Pod and the same goes for AESA radar information shared with non-AESA equipped jets in the formation. As a result, even though each aircraft is lacking a key sensor system, they all could perform almost as if they were not lacking that sensor at all by using their wingman's sensor data as if it were their own.
Under such a concept, when a squadron is not under pressure for maximum sortie generation, a Legion Pod could be mounted on an F-16 with an AESA radar as well, thus giving that individual aircraft the most capability possible. Such a setup would be ideal for the alert homeland air defense mission.

Countering The Emerging Stealth Aircraft Threat:
For the last four decades or so, the US has had total dominance in the area of stealth technology, but this is now coming to an end with China and Russia developing stealthy fighters and unmanned combat aircraft, not to mention the many countries looking to acquire stealthy cruise missiles.

Some may say that America will never get into a shooting war with Russia or China, while others say limited, regional, conventional wars among super powers over territory and access to shipping and natural resources will dominate the geopolitical domain in the coming decades. Regardless of who is right, both Russia and especially China are apt to sell their stealthy aircraft designs and weaponry to anyone with enough cash in their pocket to buy them. So confronting one of these emerging threats in the future does not necessarily mean it will happen as a precursor to a nuclear exchange during the early hours of the apocalypse.

Although these emerging stealth aircraft, drones and missiles are harder to detect, especially by X-band radars commonly used by fighter aircraft, they all have a heat signature. Even lower thrust, slower flying, very stealthy aircraft that incorporate design elements aimed at masking their heat signatures, such as buried engines and large planar "two dimensional" exhaust diffusers (like the F-117), can be detected via IRST, just at reduced ranges in comparison to their hotter fighter counterparts.

Even if airborne radars can detect stealthy targets, especially AESA arrays, this happens at reduced ranges as well, and even though you can detect a stealthy target via radar, that does not mean you have a high enough quality radar track to actually engage that target with a weapon. As a result, fielding an IRST is one of the best ways to not only detect but actually engage these emerging threats with any sort of confidence.
The USAF is clearly getting very serious about the passive detection threat posed by modern infra-red search and track systems, most notably against aircraft optimized for minimal radar observability (see F-22, B-2,F-35, RQ-170 etc). The sensor shown in the photo above, shot during RED FLAG 13-3 that concluded two years ago, is clearly a chin mounted progenitor of what would become the Legion Pod.

There are few better places to test such a capability against a wide array of US and allied aircraft alike than Red Flag, and especially on an aggressor aircraft that will be flying against all these aircraft during each sortie. In fact, the need for IRSTs on America's aggressor aircraft is quite dire as most advanced enemy aircraft around the world have had this capability (to some degree) for decades and it is clearly our increasingly stealthy fleet of combat aircraft's "Achilles heel."
The DoD has a record of coming late to the party when it comes to relatively simple, yet transformative technologies and we would have probably fared poorly against in peer-state combat for want of these systems. Examples of this include: helmet mounted sights and high-off bore-sight infrared missiles (now fielded as the JHMCS and AIM-9X), bolt-on air-to-air optimized electronic warfare pods (the same Israeli jammers made famous during Cope India now fly on USAF aggressor aircraft) and IRSTs. All these capabilities were fielded by Russian designs decades before US forces fielded similar, modern systems, or even trained against them as viable threats.
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This poor record of realizing relatively simple threats and asymmetric tactical capabilities is slowly changing and the Pentagon is becoming more open to adopting similar subsystems on their own combat aircraft.
Quite possibly the most effective place for an advanced IRST, although not a podded one, is on stealthy fighter aircraft themselves, like the F-22 Raptor. By installing an IRST system in a low observable aircraft that is already stuffed with sensors and communications gear tailor-made to feature a low probability of detection, you have a very stealthy and quiet wildcard that can see clearly even with its electromagnetic eyes closes.
Using an advanced low-probability of intercept AESA radar, like the APG-77 found in the F-22, for just an instant should keep its exact location illusive if it is operating in low probability of intercept mode, but with the IRST you have a persistent scanning and tracking ability without giving the enemy any sign you are in the area. One Raptor pilot told me that an F-22 with an advanced IRST would be "the most diabolical air-to-air killing machine imaginable."

An advanced IRST was supposed to be a part of the original YF-22A baseline design, but it was dropped due to cost and time constraints. This was a major mistake, one of many when it comes to the Advanced Tactical Fighter program and its record of predicting the actual threats America would face in the next millennium. Today, such a system would be very challenging to retrofit to existing F-22s, and since the aircraft went out of production with only 187 airframes built, there is no chance of simply building the capability into future production.
The F-35′s Distributed Aperture System (DAS) and Electro-Optical Targets System (EOTS), on the other hand, has an embedded IRST capability, although one that is said to be inferior when it comes to range and fidelity when compared with the Legion Pod's dedicated IRST21 sensor. Still, when paired with its stealthy design and cutting edge avionics, even this secondary IRST functionality should be a serious threat to enemies in the air-to-air realm, even if at only intermediate and shorter ranges.
Both Russia's T-50 and China's massive J-20, although not as stealthy as their Western counterparts, are being designed from the outset with a dedicated IRST systems in mind. On the J-20 this is presumed to be installed internally, using a trap-door mechanism to emerge from the aircraft's upper nose section when in use.

Is The Legion Pod Concept Targeted At America's Aging F-15C Golden Eagles?:
What is not clear is exactly how the introduction of the Legion Pod will effect the F-15C/D fleet. Originally, the 'Golden Eagle' roadmap (the 178 F-15Cs that will serve for decades more) had their IRST upgrade delayed. In its place, off the shelf Sniper targeting pods are being deployed as a stopgap measure.

The fact is that the Sniper pod, which was built for the ground attack laser targeting mission, is being used "off label" by the F-15C fleet. Although it may provide longer-range imagery of aerial targets than an actual IRST, it presumably has to be cued by the F-15C's radar in order to know where to look when it comes to pickup up targets at long distances. Any latent IRST-like search and track capability should be vastly inferior to an actual IRST sensor system like the IRST21 found in the Legion Pod. As such, it really is a 'poor man's' IRST of sorts, although it is aimed more at identifying targets visually at great range than scanning the skies for them in a real near peer state combat scenario. Also, its location under the aircraft gives it a large obstacle when viewing closer, higher altitude targets.

The Sniper pod may be a decent solution for the homeland air defense mission, as identifying a target visually, especially at night and at long distances, is hugely important for such a demanding mission. Yet it still does not give the F-15C the passive detection, tracking and engaging capability it could really use, nor does it address the need to be able to detect low-flying stealthy cruise missiles that can be fired off of commercial vessels operating clandestinely off the coast of the US mainland.
This is where the Legion Pod makes sense for the F-15C. If the F-15C community were to receive the pod, doing so would finally fill a unique capability gap. Additionally, when combined with the F-15C's new AESA radar, the most capable of its kind in the world, and its upcoming digital defensive electronic warfare suite, it would really give the Eagle the tools it needs to remain relevant for decades to come. Also, although a podded sensor mounted below the jet is not ideal due to line of sight issues and because it takes up a critical weapons station, the fact that Legion Pods can be swapped out for Sniper Pods when an aircraft is on alert air sovereignty duty back in the US makes a lot of sense. Incidentally, Japan actually has tested an IRST mounted on the nose of one of their F-15Js. The exact program details remain secretive, but the fitment and mounting location seems perfect for such a device.

Searching For Conclusions, Tracking More Questions:

IRSTs do have a couple weaknesses.

First off, if it is installed in a podded system it will take up a stores station that could be used for more fuel and weapons. Second, their effectiveness can be degraded by atmospheric conditions to some degree. This does not mean an IRST will become ineffective on a stormy day, but those storms may reduce its scanning range. They also have certain secondary advantages, such as providing an image of your target at closer ranges and being able to possibly detect and track missile launches at very long ranges, both from the ground and the air.
There is little doubt that the Legion Pod is an exciting addition to the menu of options the Pentagon has for dealing with emerging threats and its rapidly aging fighter fleet. In addition to acting as an enabler for a whole slew of potential tactics and a force multiplier when paired with data links, it also provides a potent fall-back playbook from the normal highly networked and electromagnetic spectrum dominating air warfare concept that US air power has become more and more dependent on year after year.
Although such a sensor really should have been retrofitted into America's fighter fleet years ago, the Legion Pod be an affordable, adaptable and asymmetric edge that cannot be passed up. At the very least, our aggressor squadrons, USAF, Navy and Marine, should be funded to field the pod immediately, as the Pentagon is living in denial of a very real and capable threat that that is prevalent throughout the world and that we don't appear to be training our pilots to deal with in any realistic manner.

Then again, if our aggressors need this capability so badly in order to prepare for combat with potential foes, then maybe that is a strong enough reason in itself to field that same capability across America's 4th generation fighter fleet.
In the end, the Legion Pod may not be sexy, but paired with the proper tactics, it could be a very deadly enabler and even a downright necessary addition when it comes to retaining America's air supremacy over the uncertain battlefields of the future. At the very least, it is a relatively affordable insurance policy for the real possibility of a situation when our radars and data-links that we so heavily rely on today are greatly degraded by our enemies of tomorrow.
All photos via DoD, Lockheed Martin, Public Domain aside from: SU-50 via wikicommons/Rulexip, T-50 and SU-35 break via Wikicommons/Oleg Belyakov, F-16 Aggressor IRST during Red Flag via our good friend Mark Munzel.
Tyler Rogoway is a defense journalist and photographer who maintains the website Foxtrot Alpha for You can reach Tyler with story ideas or direct comments regarding this or any other defense topic via the email address [email protected]