Actually, the USAF introduced IRST pods before the USSR air branches.
Infrared Search and Track was invented by Texas Instruments, further developed by Hugues Aircraft and by 1967 Crusaders and F-4 Phantoms were equipped with IRST pods during the Vietnam War, half a decade before the Flogger B (MIG-23M) ever went into production in 1972!
The USAF and USN pilots feedback was that IRST was beyond useless and gave no operational benefit due to blurry image quality and low detection ranges. This lead the USA’s decision to leave IRST on the backburner for a couple of decades.
The reason the USSR was more active with IRST/FLIR integration on their airframes is simple. The USA has a knack for airframes with low RCS since the SR-71.
Soviet radars just could not keep up with the USA’s technological rupture on that field.
If soviet aircraft started to be equipped with FLIR, it is primarily because they are tasked to respond to a particular threat (defend a large airspace against stealthy USAF bombers or below radar intruders).
Moreover, when you have mediocre radars, you have to compensate elsewhere, aka infrared cameras.
Seeing the Soviet FLIR/IRST buildup coincides with the USA’s stealth buildup I correlate Soviet intel was good enough they knew more USA stealth aircraft were incoming, such as the F-117 Nighthawk, A-12 Avenger II, YF-22, YF-23 and B-2 Spirit (Hell they caught a guy trying to sell info on the ATB program to the soviets in the 1984).
So there you have it, it had nothing to do with pushing IRST to passively track and engage enemy bandits in a high intensity war.
Mostly because the operational value of those early systems is null, and radar did that job better against most western airframes anyways as the bulk were non-stealth.
Unless MIG-23/27/29 feel suicidal enough to get within 10 km or less of an F-15 or F-16 squadron just to get a final firing solution from the IRST+FLIR whilst the Eagles or Falcons snipe them Beyond Visual Range…
To sum up, integrated IRST presented no operational benefit in a conventional shooting war scenario, it was useful against stealth bombers harassing the vast Soviet airspace but that’s it.
Meanwhile optronics pods like Litening, Lantirn, Sniper, Legion, Damocles, Talios can do all the things integrated IRST can do, but much better, on any combat plane able to fusion the pod’s sensors feed.
Simply because most integrated IRST tech dates from the mid 80s to late 90s and haven’t been overhauled since then.
Then, semi-conductors, CMOS image sensors and camera tech overall saw an exponential growth in quality and capabilities by the late 2000s. This is mostly linked with the digital revolution on the consumer market: RED Cinema, GoPro, smartphone cameras, dash cams you name it.
So right now, IRST is back in force because the civilian market did a good job miniaturizing powerful optics and sensors with excellent semi-conductors and modules to process the raw data.
Hell, I call BS on all those nice brochures singing praise about the Su-27 and MIG-29 integrated IRSTs, because even the ones on the Rafale, the Eurofighter Typhoon and the F-35 are already considered obsolete by targeting and recon pod standards.
The advertised detection ranges on any integrated IRST+FLIR are as BS as my USB 3.1 Gen 2 port reaching 10 gigabit/s transfer speeds.
French feedback on Optronique Secteur Frontal (OSF) performance during Afghanistan, Libya and Mali was that integrated IRST had no tangible operational benefit and that pilots preferred the much more capable Damocles pod.
Actually, the entire Tranche 3 of Rafale ditched the OSF altogether because it was a wasteful redundancy seeing pilots used the Damocles pod anyways, and those little balls and bumps housing the IRST between the nose and the canopy actually hurt aerodynamic performance of the plane (they tested in on Mirage 2000s and they actually kept it from reliably going above Mach 2 at high altitudes).
French Air Froce and Navy have opted to rely on the new TALIOS pod for IRST on the Tranche 3 Rafales.
However, there will be a brand new integrated OSF for the upcoming F4 standard.
For the near future, the Talios pod will do IRST much better than both the archaic OSF and older Damocles pod and we will have to wait and see if the new OSF-IT can match or beat TALIOS once introduced.
Eurofighter Typhoon's pirate IRST is newer, first introduced in 2007, but can't track ground targets and ranges are not that much better than on the older French OSF. Typhoons use Litening or Damocles pods for recon and strike missions anyways.
Concerning the F-35, EOTS integrated IRST is already considered outdated because it’s based on an older Sniper module, and the bloody plane is not even operational yet! When it reaches operational status by the late 2020s, EOTS will be downright obsolete.
In my opinion it’s much easier and cheaper to just swap pods every decade than to overhaul integrated IRST, because the pace of image sensor quality and processing power is exponential these days.
Lastly, Russians have been getting all their critical optronic components from French companies (THALES/SAFRAN) since the late 90s, be it MBT thermal cameras or aircraft/helicopter IRSTs. Now due to sanctions the Russian defense industry can’t get French optronics anymore. Curious how European sanctions hit Russia in 2015 and all their lavish defense programs fall flat…
Still don’t believe me soviet era IRST and FLIR were terrible, here’s a visual aid:MIG-23MF IRST feedRafale OSF feedRafale OSF Video
By the way I can't find any footage or captures from Soviet/Russian IRSTs besides the one I just linked, especially MIG-29's, feel free to share if you happen upon those.
P.S : No the Foxhound is not stealthy, it's a big ass plane with no RCS reduction features, huge reactors and exhaust and non-stealthy commlinks because stealthy commlinks are exclusive to the F-22 and F-35 so far. If turning off the radar is what you consider stealth, then every airplane can be stealthy.