The AGM-122 “Sidearm” anti-radiation missile (ARM) is one of the more obscure operational missile systems within the annals of air combat history, but how it came to be was pretty creative and we probably could use something very similar to it today.
The history of the legendary Sidewinder air-to-air missile reads like alphabet soup, with dozens of variants carrying different letter designations, all of which were designed, tested, and in many cases deployed operationally over the last six decades. These have included a surface-to-air variant, the MIM-72, that equipped the M48 Chaparral short-range mobile air defense system, the air-to-ground AGM-87 Focus, and even a variant intended to defend submarines trying to hide from the prying eyes and ears of maritime patrol aircraft and anti-submarine warfare helicopters. But the AGM-122 version of the Sidewinder is maybe the most novel, and its genesis is actually a tail of two Sidewinder types, the other being the short-lived AIM-9C.
In the late 1970s, it was becoming clear that the Pentagon needed a light-weight anti-radiation missile capable of being deployed on attack helicopters—namely the upcoming AH-64 Apache and battle tested AH-1 Cobra. These helicopters could find themselves operating near or being threatened by enemy radar guided air defenses. Because of its size, the missile could also theoretically be deployed aboard attack jets that provide close air support in the place of short-range air-to-air missiles.
Adapting the hugely popular AIM-9 Sidewinder’s basic design for this requirement made the most sense as doing so would save on development and production costs, and ease aircraft integration. But building new AGM-122 “Sidearm” derivatives of the Sidewinder was not to be. Instead the program came up with a novel idea to reutilize an existing defunct Sidewinder variant to satisfy its lightweight anti-radiation missile requirements.
The AIM-9C Sidewinder, sometimes referred to as the “radar Sidewinder,” was built specifically for the F-8 Crusader in the early 1960s. The missile was the same as the AIM-9D in many ways, but instead of an infrared seeker it utilized a semi-active radar homing (SARH) seeker that could engage targets “painted” by the F-8’s radar. The main advantage of using SARH over infrared guidance was that the missiles could be used to make head-on “face shots” on enemy aircraft, something the Sidewinders of that era could not do. Instead they would require the F-8 to maneuver to the rear aspect of its target in order for the infrared seeker to acquire the enemy aircraft’s hot exhaust. Radar guided Sidewinders could also be more easily employed in all weather environments and at night.
About 1,000 AIM-9Cs were built but the concept was short lived due to limitations of the F-8’s radar and fire control system. As a result, large stocks of the missiles existed two decades later, long after the F-8 had ceased fighter operations, and at a time when the AGM-122 program was coming to fruition. The Sidearm conversion basically saw the fitment ofa wide-band passive electromagnetic radiation homing seeker in place of the AIM-9C’s existing narrow-band SARH seeker, as well as overhauling the missiles other components, and the fitting of a new fuse section and updated rocket motor used by the AIM-9L/M.
Think of it as a ingenious missile recycling program of sorts.
The general configuration was tested at NAWS China Lake in 1981 and was deemed a success. By that time the Army had lost interest in the program, but the USMC pushed on in an initiative to deploy the lightweight anti-radiation missile on their AV8 Harriers, A-4 Skyhawks and AH-1 Cobra attack helicopters.
A contract to convert the remaining AIM-9C stocks to the AGM-122A configuration was won by Motorola in 1984 and the conversions began in 1986. By 1990, the last of roughly 700 AIM-9Cs became AGM-122As.
The missile could lock on to a wide variety of enemy radar systems and chase them down even if they are on the move, albeit at relatively close ranges of around nine miles on paper, but often far shorter ranges in reality since the weapon was to be fired from low altitudes. Anti-aircraft artillery and short-range air defense systems (SHORADS), such as point defense SAM emplacements and mobile vehicle mounted anti-air systems were the missile’s primary targets, but it could also be used to attack enemy vessels that were emitting threatening radar energy. It was an incredibly simple but effective weapon.
Once fired, the missile was programmed to enact a “pop-up” maneuver so that it could make a diving terminal attack on the emitter being targeting. Although it lacked the standoff range, speed or advanced processing power of AGM-88 High-Speed Anti-Radiation Missile (HARM), it was still relevant. The one caveat being that the aircraft carrying it would have to get comparatively “down and dirty” with the threat in order to kill it.
Also it should be noted that the Sidearm was intended to destroy the radar emitter—the antenna basically—and not the armored vehicle or the surrounding infrastructure it is mounted on. In other words, it’s a suppression of enemy air defenses weapon intended to exact a “mission kill” on an enemy air defense system, not obliterate it and its controllers entirely. The same continuous rod fragmentation warhead was used in the AGM-122 as the AIM-9C, which gave it limited destructive ability, but a high probability of causing a fatal impact on the emitter itself.
In the end, the Sidearm was primary fielded by the USMC on its Cobra attack helicopters and AV8 Harrier jump-jets. Over the years the missiles were slowly fired off or went out of service as their expiration dates were reached. A much more capable and reprogrammable successor was planned to be built from scratch, dubbed the AGM-122B, after all the AIM-9Cs were converted, but funding from the services for this extension of the program never materialized.
The Sidearm story is a relevant one not just because it showed how repurposing an existing platform can be a viable proposition and economically beneficial, but also that a light-weight ARM is really more relevant today than it was 30 years ago.
Today’s modern ground-based air defense systems are increasingly mobile and lethal. Systems like Russia’s Pantsir S1, 2k22 Tungusta and Tor short-range mobile air defense systems, and many others from other countries, both friendly and not so friendly, have proliferated around the globe dramatically. These systems are hard to pinpoint and destroy using conventional suppression and destruction of enemy air defenses (SEAD/DEAD) tactics and can “pop up” virtually anywhere.
Advanced helicopters with capable radar warning and homing receivers may be able to detect the presence of these systems, after which they can try to avoid or attack them, but having the option to suppress them without having to mount a traditional strike on them would be beneficial. An updated version of the Sidearm, that can pop-up from low-level and detect, and then home in on and destroy an enemy emitter, without putting the helicopter at direct risk, could be a very useful tool on the anti-access battlefields of tomorrow. The USAF’s A-10 Warthog fleet, which is supposed to serve at least to 2030 now, could also benefit from such a weapon, as could a light attack turboprop aircraft should the USAF actually field one once and for all.
Basing such a design on the newest version of the Sidewinder, the AIM-9X, would make a lot of sense, and would offer enhanced kinematic performance over the AGM-122, but one short-range missile already has the capability to home-in on emissions from enemy radars—that being the small but highly agile RIM-116 Rolling Airframe Missile (RAM).
This missile is used as the primary point-defense weapon for US Navy and many NATO ships. Like the AGM-122, it uses components of the Sidewinder for its basic platform, but has a dual-mode seeker that rapidly homes in on enemy missile radar emissions as well as incorporating the infrared seeker from a FIM-92 Stinger man-portable air defense system (MANPADS). It uses both these systems to reliably lock onto and engage incoming enemy anti-ship cruise missiles, some of which can crest the horizon at supersonic speeds.
A simplified version of this missile omitting the infrared seeker and with specialized autopilot programing could give American helicopters and low-flying attack aircraft the rapid-reaction enemy air defenses killing capability they need. Not just that, but they could likely be programmed to sniff out and kill other emissions, such as radio signals and data-link emissions. If the infrared seeker was left on, they could be able to work as a dual-role missile, able to smash enemy radar emitters and take out other helicopters and low flying aircraft, as well as drones, at short ranges.
So in some ways, the AGM-122 can be seen as almost as a proof of concept program, a forerunner to a much more capable, but also relatively off-the-shelf missile that can be adapted for similar and expanded uses. Think of it as the Sidearm II. But it all comes down to there being a will in the services to back such a project. At this time there doesn’t seem to be, which seems odd. Heavy reliance on electronic warfare and enhances situational awareness may be to blame for this. But now that the A-10 will be around for a long time to come, and a fleet of light air support aircraft may begin doing the duty of fighter aircraft for lower intensity conflicts, not to mention thegrowing threat of drones, maybe the Sidearm concept’s time has finally come.
Contact the author: Tyler@thedrive.com