The U.S. military's biannual Northern Edge exercise is in full swing in Alaska and a picture has emerged showing an F-15C Eagle taking part in the drills while carrying a Lockheed Martin Legion Pod. This system has an infrared search and track sensor, or IRST, which offers the pilot an important additional way to detect and track other aircraft at significant ranges. The Air Force doesn't expect this system to reach initial operational capability until next year, but it's no surprise it has appeared at this exercise, which has long served as a valuable opportunity to test new advanced aircraft and systems and the fighting doctrine associated with them.

Pacific Air Forces (PACAF), which manages the exercise, posted the picture of the F-15C, which carries the "WA" tail code of Nellis Air Force Base, on May 15, 2019. The caption does not say what specific unit the plane belongs to or mention the Legion Pod. The base is home to the 57th Wing, which, among other things, manages the prestigious U.S. Air Force Weapons School. Nellis is also responsible for managing the adjacent and sprawling Nevada Test and Training Range (NTTR) and the base hosts a wide variety of test and evaluation units. This iteration of Northern Edge is a particularly large event, involving approximately 10,000 personnel and some 250 aircraft from across the services. "The exercise is designed to sharpen participants’ tactical combat skills, to improve command, control and communication relationships, and to develop interoperable plans and programs across the joint force," according to an official statement. F-15Cs are regular participants in the biannual exercise and the aircraft with the Legion Pod is only one of a number of Eagles taking part in the drill.

USAF An F-15C Eagle from Nellis Air Force Base flies over Alaska while carrying a Legion Pod during Northern Edge 2019.

The Air Force's fleet of around 220 F-15C/D Eagles remains a critical part of the service's air-superiority capabilities, both at home and abroad, after decades of service. There had been talk in recent years about retiring the jets for good and there is now a push to replace these aircraft with new production F-15Xs, which you can read about in more detail here and here. In the meantime, the Air Force is continuing on its "Golden Eagle" upgrade path to give the F-15C/Ds important capabilities to ensure they remain relevant in the coming years. This has included efforts to add powerful AN/APG-63(V)3 active electronically scanned array radars, conformal fuel tanks, and new cockpit displays, as well as integrating Lockheed Martin's AN/AAQ-33 Sniper Advanced Targeting Pod (ATP) on the jets. The latter system offers a long-range identification capability, day or night, as well as a secondary intelligence, surveillance, and reconnaissance functionality. It primarily finds its targets by slaving the optics to the F-15C's radar. The pilot can also manually steer the Sniper ATP's camera or can cue it to their Joint Helmet Mounted Cueing System (JHMCS). It also offers something of tertiary "poor man's" IRST-like capability, but nothing near as capable as a dedicated IRST system, such as the IRST21 in the Legion Pod.

USAF A pair of F-15Cs from the 48th Fighter Wing at RAF Lakenheath in the United Kingdom equipped with Sniper ATPs after recently arriving in the Middle East.

The AN/ASG-34 IRST-equipped Legion Pod offers far more robust and automated functionality and can quickly spot and track multiple targets at far beyond visual range. It also provides actual targeting information so the pilot can engage threats using the IRST for targeting alone, or in conjunction with other sensors, which offers important advantages. This additional means of spotting, tracking, and engaging aircraft passively eliminates the chance of alerting potential opponents that they've been detected, unlike radar that can give away the attacking aircraft's presence and even its location. On top of all this, the IRST provides an alternative to the radar in electronic warfare-heavy (jamming) combat environments and radar-evading design features on stealth aircraft have no effect on the IRST. It depends on the aircraft's infrared signature alone.

USAF A large portion of the Eagle test fleet is taking part in Northern Edge 2019.

USAF A specially equipped, Edwards AFB based, test F-15C takes gas during a Northern Edge sortie.

Lockheed Martin developed the IRST21 sensor from the AN/AAS-42 IRST system it had supplied for the F-14D Tomcat. Another version of that earlier sensor system, known as Tiger Eyes, also found its way onto newer export versions of the F-15E Strike Eagle. You can read much more about the IRST21, its predecessors and the capabilities IRST sensors offer, in general, here. The Legion Pod flew for the first time on an F-15C in 2016, having already gone through trials on an F-16 Viper the year before. In 2017, the Air Force picked the Lockheed Martin pod over Northrop Grumman's OpenPod and work has been ongoing since then to fully integrate into the service's Eagles. As of November 2018, the Air Force's plan was still to reach initial operational capability with the system on the F-15C in 2020.

Lockheed Martin

The Legion Pod on the F-15C is just another example of the IRST21's growing popularity within the U.S. military, as well. U.S. Navy Block III F/A-18E/F Super Hornets are also getting this sensor, coupled with a modified centerline drop tank. Lockheed Martin's IRST21 is also a feature on the Air Force's Talon HATE communications node pod, which you can read about more here. IRST capability is likely to be just one feature of the Legion Pod on the Air Force's F-15C as time goes on, too, and the system could easily migrate to other platforms in the future. From the very beginning, Lockheed Martin has touted the pod's open-architecture design and available extra payload space, which could accommodate additional sensors, electronic warfare systems, communications equipment, and more.

Lockheed Martin