Just over fifty years ago, the USAF flew a mission for the first time dedicated to suppressing SA-2 Surface to Air Missile sites in North Vietnam. In spite of the US Army having widely deployed a very similar system domestically for years, the Air Force knew little about the best way to accomplish the mission, which came to be known as Wild Weasel, or more properly, Suppression of Enemy Air Defenses, or SEAD. Tactics, techniques and procedures (TTP) would emerge along with new weapons and technology.
The first dedicated weapon for this SEAD mission was the AGM-45 Shrike, a missile derived from the AIM-7 Sparrow with a passive seeker that homed in on the electromagnetic power radiated by a radar set. Hence the term Anti-Radiation Missile, or ARM.
The Shrike had a few issues, however. Most critically, it had a shorter range than the SA-2 it was intended to counter. But it also had another glaring weakness. If the radar it was attacking suddenly stopped transmitting, it had no means to guide to the target, and would miss.
Still, the mission was suppression of enemy air defenses. By forcing radar operators to shut down, even for a short while, that allowed the main strike package to transit and strike its primary target.
Unfortunately, that simply meant the same suppression would have to be undertaken day after day. The later AGM-78 Standard ARM and its replacement, the AGM-88 High Speed ARM, or HARM, attempted to avoid the shutdown defense by integrating a strapdown Inertial Navigation System (INS) that would guide the missile to the last known position of the emitter. Unfortunately, many modern SAM radars, particularly short range systems, and extremely mobile. Nor were early INS systems particularly accurate. The shutdown still meant most radar systems survived attack.
The frustration of having to repeatedly spend sorties, time, and ordnance on enemy air defenses lead to something of a doctrinal shift, particularly after Desert Storm and the 1999 air campaign over Kosovo. Emphasis shifted from suppression to Destruction of Enemy Air Defenses, or DEAD (usually pronounced “dee-ad” as opposed to “dehd”). While jamming and HARM would be used to suppress radar guided SAMs, the attack would be pressed and launchers, radars, control sites and communications nodes would be attacked with either conventional munitions, or guided weapons such as Laser Guided Bombs (LGBs), the GPS guided Joint Direct Attack Munition (JDAM) or the gliding GPS guided Joint Stand Off Weapon (JSOW).
The improvements in guidance technologies led the US Navy to reexamine the state of the art in ARMs.This became the Advanced Anti Radiation Guided Missile program, or AARGM. Money for an entirely new ARM wasn’t available, but some funds were, so research began. What they found was that the basic HARM motor and airframe were generally acceptable. The improvements in technology, however, meant that a far more capable seeker system was possible.
What resulted was the AGM-88E HARM. Externally virtually indistinguishable from its predecessors, the AGM-88E uses a much improved passive radar seeker. It also uses a datalink receiver known as Intergrated Broadcast System- Receiver (IBS-R) to receive positional data on threat emitters gathered by Electronic Intelligence (ELINT) platforms such as the EP-3E and RC-135. It also uses a GPS updated INS platform for better guidance. Finally, it has a millimeter wavelength active radar seeker for terminal guidance.
AARGM is in service with the US Navy and Marines. And having just entered service in 2012, the Navy is now looking at a further upgrade, with an RFI issued recently seeking to increase the missile range, most likely through an improved solid rocket motor. What is interesting is that the RFI also lists as a threshold capability internal carriage on the F-35A/C (due to the lift fan, the F-35B has a slightly different internal weapons bay layout).
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