Though details remain limited, the Houthis got worryingly close to downing a U.S. F-35 Joint Strike Fighter, and reportedly several American F-16 Vipers, during a surge in airstrikes on targets in Yemen this spring. Houthi air defense capabilities are largely rudimentary, but this also makes them a unique and vexing challenge for American combat aircraft. Made up of mainly mobile systems, they can appear virtually anywhere, disrupting carefully laid mission plans. Many of them are also improvised, leveraging non-traditional passive infrared sensors and jury-rigged air-to-air missiles that provide little to no early warning of a threat, let alone an incoming attack.
Last month, TWZ published a deep dive feature on the Yemeni militants’ air defense arsenal that you can access here. You can also get up to speed about what is known about the Houthis’ attempted intercepts of U.S. crewed combat jets earlier this year in our initial reporting here.
Houthi air defenses appear to have prompted an increased use of stealthy aircraft like the F-35, especially for direct strikes on targets in Yemen, as well as costly standoff munitions, in recent months. The U.S. military launched its expanded campaign of strikes against Houthi targets in Yemen, dubbed Operation Rough Rider, in March. Last week, the U.S. government announced a ceasefire with the militant group, which authorities in Oman had helped broker.
As it stands now, it is unknown what missile or missiles the Houthis fired at the F-35. Other details that would allow for a full assessment of that engagement, as well as the reported attempted intercepts of the F-16s, are yet to emerge.
To provide some general context, when it comes to the F-35, on top of its stealth design, the jet has a powerful built-in electronic warfare suite, as well as the ability to employ expendable countermeasures and the capacity to use towed decoys. However, this does not mean it is invulnerable to detection or interception, as TWZ has previously written:
“The F-35 … is designed with its own highly-integrated, highly-advanced AN/ASQ-239 electronic warfare system. It takes advantage of its active electronically scanned array (AESA) radar and the antennas that are buried along the edges of its wings and control surfaces and beneath its skin. This capability allows the F-35 to ‘self-escort’ to the target area and back, taking on enemy emitters electronically that it may have trouble staying far enough away from to evade detection entirely. This same electronic warfare suite and the jet’s high degree of sensor fusion offers F-35 pilots the ability to make rapid decisions regarding their survivability on the fly. They can decide to destroy threatening emitters that may pop-up in their way, and new weapons are being developed to do this quickly and over relatively long ranges, or to avoid the threat entirely if possible, or to try to blind and confuse it via electronic attacks, allowing the F-35 to sneak by unscathed.”
“This electronic warfare capability gives the jet an enhanced degree of survivability and helps offset reliance on its low-observable design alone, which does have its weaknesses. Beyond being optimized to defeat higher-frequency fire control radars, like those that operate on and around the X band, the rear of the F-35 has been a bit controversial as its perceived radar cross-section is larger than some would like, possibly leaving it vulnerable to detection and even engagement from rear aspects.”
Even in its most stealthy configuration, an F-35 also has to open its internal bays to employ air-to-air and air-to-ground munitions, which offers an enemy a brief opportunity to detect it at much greater distances on radar.
As already noted, a central aspect of the air defense arsenal the Houthis have been able to cobble together over the past decade or so is the use of infrared sensors for target detection, tracking, and cueing, and as seekers in the interceptors themselves.
The Houthis have stocks of infrared-guided R-73 and R-27 air-to-air missiles repurposed for surface-to-air use, which are referred to locally as Thaqib-1s and Thaqib-2s. The Yemeni militants also have Saqr-series infrared-homing surface-to-air missiles that have a degree of loitering capability. They are based on an Iranian design commonly referred to simply as the “358.” The ability of Saqr/358 missiles to engage higher and faster-flying combat jets is likely somewhat limited, but the Thaqib-1/2s have demonstrated their ability to at least hold fighters at risk in the past, which we will come back to later.
The Houthis also regularly release infrared camera footage after claiming surface-to-air intercepts of U.S. and other foreign crewed and uncrewed aircraft. This, in turn, points to the possibility that Yemeni militants are also using infrared sensors for target detection, tracking, and cueing beyond just for infrared missile types, including with various radar-guided surface-to-air missile systems, such as more modern types fielded in recent years with the aid of Iran.
Unlike active radars, infrared sensors and seekers are passive in nature. This means they do not emit signals that an electronic warfare suite like the AN/ASQ-239, or other RF warning sensors, can detect to alert pilots that a threat is present, and especially that their aircraft has been spotted and is being targeted before and after a missile is launched. This presents challenges to stealthy and non-stealth aircraft alike.
At launch, an F-35 should be able to detect the incoming missile using its AN/AAQ-37 Distributed Aperture System (DAS), which consists of an array of six infrared cameras installed in various locations around the aircraft. However, the time available for the pilot to react could be very short at that point, especially if there was little to no advance warning. An aircraft without electro-optical and/or infrared missile launch detection/approach warning capabilities would have to rely first on visually spotting the incoming infrared-guided threat before even attempting any evasive action.
Pairing infrared sensors with radar-guided surface-to-air missile systems could also help them remain hidden by not having to start radiating until very late in their engagement cycle. This would reduce the available time for a targeted aircraft to react. It would also aid in cueing the fire control radar onto stealthy targets.
“The Houthis and the Iranians went electro-optical, because it is a completely passive system,” Michael Knights, a senior fellow at The Washington Institute for Near East Policy, a think tank in Washington, D.C., had told CBS News for a story published last September as U.S. MQ-9 drone losses to the Houthis had already started to stack up. “It’s hard to hunt those things down because they don’t really have any signature before launch.”
It’s important to note here that the ability of Houthi air defenses to punch above their weight by leveraging lower-end infrared capabilities is not new, and in many ways has been an advantage for them for the reasons stated above. The Yemeni militants also claimed to have damaged or destroyed Tornado, F-15, and F-16 crewed combat jets, as well as drones, belonging to Saudi Arabian-led forces during fighting in the late 2010s and early 2020s.
Though a firm tally has not been established, significant losses of U.S. MQ-9 Reaper drones to the Houthis are well-documented and otherwise substantiated at this point, as well.
Regardless of infrared sensor assistance, road mobile radar-guided systems remain a problem for U.S. and allied combat aircraft, not just in Yemen, but anywhere. At a hearing before the House Permanent Select Committee on Intelligence in March, U.S. Air Force Lt. Gen. Jeffrey Kruse, head of the Defense Intelligence Agency (DIA), confirmed that the Houthis had “attempted to” use their Soviet-era mobile 2K12 Kub (SA-6 Gainful) radar-guided surface-to-air missile systems, specifically, against U.S. aircraft, but did not elaborate.
Mobile systems, including the 2K12/SA-6, are understood to make up the majority of the Houthis’ air defense capabilities, making it easier for them to ‘pop up’ suddenly in unexpected locations, which presents even more challenges. In addition, this makes it more difficult to target them proactively and plan the most effective and safest mission routes. For the F-35, this reduces the advantages the stealthy jet otherwise has, in part thanks to advanced mission planning support used to devise optimal routes based on detailed data about hostile defenses and other recent intelligence, while also taking into account the aircraft’s signature, defensive capabilities, and more. All of these elements are factored into a ‘blue line’ route that is calculated as the best path for survivability and overall mission success. This route will have lower efficacy when road-mobile surface-to-air missiles and improvised infrared threat systems are present.
The U.S. military is also well aware that stealthy aircraft are not invisible or invulnerable to enemy air defenses, in general. Serbian air defenders proved back in 1999 that radar cross-section reducing design features do not eliminate risk when they shot down a U.S. F-117 Nighthawk stealth combat jet and succeeded in damaging another on separate occasions with then-dated Soviet-era surface-to-air missiles. F-117 missions at that point in time were already being routinely conducted with support from EF-111 Raven and EA-6B Prowler electronic warfare aircraft, something notably absent on the night that the one Nighthawk was lost. The Serbians had also gotten advance warning that a group of F-117s was on its way, and the jets reused what had become a well-known route to the target area, making it easier to set an ambush for them.
Even today, U.S. stealth aircraft like the F-35 and the B-2 bomber make use of offboard electronic warfare and suppression and destruction of enemy air defenses (SEAD/DEAD) support, provided by non-stealthy aircraft, during missions when possible. A host of factors, including a certain amount of luck, can still coalesce and lead to them getting shot down. Had the Houthis been able to shoot down an F-35, or even a non-stealthy U.S. fighter, or just severely damaged one, for any combination of reasons, it would have been a major propaganda coup and humiliating for the United States. Had a pilot been killed or captured, it would have added an even more mortifying dimension to the incident.
The U.S. military as a whole has already acknowledged that operations against the Houthis have provided the opportunity for very important lessons to be learned. The potential loss of an F-35 or any other crewed aircraft to Yemeni militants would be something worth scrutinizing, regardless of the circumstances.
It’s also worth noting here that the loss of a jet over Yemen would have likely led to a combat search and rescue (CSAR) effort requiring significant manpower and material resources. Dispatching a force including low and slow-flying helicopters or Osprey tiltrotors supported by additional fast jets into an area where air defense threats had already downed one of the U.S. military’s most survivable aircraft would present massive additional risks. The U.S. military has already been facing growing questions about how it plans to respond to the loss of stealthy aircraft in highly contested environments in future high-end conflicts.
Interestingly, just this past weekend, CENTCOM shared pictures of Air Force HH-60W Jolly Green II CSAR helicopters operating in the Middle East.
All of this has ramifications for the U.S. military well beyond the F-35 and Yemen. Infrared search and track systems (IRST) on hostile aircraft and platforms down below, along with other infrared sensors and longer-range anti-air missiles with infrared seekers – all far more advanced than what the Houthis have been employing – are becoming increasingly more common components of the aerial threat ecosystem. Those systems will also increasingly be tied into larger and deeply networked integrated air defense systems (IADS), where they can then be used to help cue radars to targets of interest, especially stealthy ones.
With infrared sensors having identified a stealthy target, operators could use their radars in non-traditional ways, or cooperatively in an automated fashion, to create a target-quality track. If they can’t lock on immediately, the position of the target could be relayed to aircraft or other assets, including ever-problematic road-mobile air defense systems, which might be better positioned to attempt an intercept. They could also use the passive sensors to continue tracking the target until better conditions for a lock emerge — namely being in closer proximity to a fire control radar or a group of them that are networked across the IADS.
Emphasis on infrared and other passive sensors capabilities is only likely to be further fueled by the continued fielding of stealthy aircraft, crewed and uncrewed, as well as missiles, by more and more countries around the world. What the U.S. Air Force has referred to at least in the past as “spectral warfare” and “spectral dominance” has already been a major aspect of that service’s Next Generation Air Dominance (NGAD) initiative for years. Technologies to help shield aircraft against IRSTs and other infrared sensors are a key element of achieving that ‘dominance.’
Potential adversaries like China and Russia have been learning the same kinds of lessons, now with the help of observations from the recent fighting in and around Yemen, as well as the ongoing conflict in Ukraine.
More details about just how close the Houthis actually came to shooting down an F-35 or other crewed U.S. aircraft may now continue to come out. What has emerged already is that the Yemeni militants have demonstrated the real threats that mobile air defense systems, and especially those that leverage infrared detection and tracking capability, can present even to advanced stealthy aircraft.
Contact the author: joe@twz.com