One of the many reasons China does not want foreign (especially American) ELINT (electronic intelligence) aircraft anywhere near their coastal waters is because of the progress China is making developing new military electronics and, more importantly, weapons for defeating or simply finding and destroying enemy electronic systems. This is particularly the case with Chinese HARM (high-speed anti-radiation missiles) developments.
China has been building these since the 1990s, starting with the Russian Kh-31P (both those it purchased and then built under license). After 2000 Chinese missile manufacturers developed optional anti-radiation guidance systems for their air-to-air missiles. This produced the CM-102 and LD-10 HARMs. China does not export the latest versions of these to foreign customers. The CM-102 and LD-10 are more similar, in appearance, to the American HARM because these all use solid fuel.
The original Chinese HARM was based on Russian work and that was upgraded as well. In 2009 it was revealed that China had upgraded 200 Russian Kh-31P HARM it imported in the 1990s. The Chinese were dissatisfied with the Russian seekers (that detected and homed in on radar transmissions) and developed one of their own. The Chinese seeker detects more radar frequencies (2-18 Ghz) and will hit within 8-10 meters of the radar transmission. China called its version of the Kh-31P the YJ-91 and it is still produced, despite its use of liquid fuel, because of its high speed and reliability.
The Kh-31 was originally developed as an anti-ship missile. The Russians quickly realized that, with a different seeker, the missile would also work well as an anti-radiation weapon. The anti-ship version has a range of 50 kilometers, while the ARM version is good for 110 kilometers. The .6 ton missile has an 87 kilogram (191 pound) warhead. SEAD (Suppression of Enemy Air Defenses)
Since the late 1990s China has been trying to keep American recon aircraft away from their coastal areas to prevent these aircraft from detecting and recording activity by Chinese air defense systems and other military electronics. Carefully analyzing these systems from a distance (international waters are anything at least 22 kilometers from the coast) reveals vulnerabilities that U.S. could exploit in wartime. This is doubly troubling to the Chinese because the Americans are known to share this kind of information with their allies, especially Taiwan, South Korea and Japan.
Yet China is building more ELINT ships and aircraft and these are always nearby when American naval forces hold training exercises, especially if it is done with American allies equipped with American and other Western equipment. This has always been the case when the U.S. comes to the training even with their own AGM-88 HARM. These come in various models, giving foreign users lots of options. Some export customers still buy the older AGM-88Bs but China is most concerned with the recent AGM-88E and AARGM models which Australia recently bought.
One reason the E model is so popular is that is capable of going after moving ships. This makes the AGM-88E an effective anti-ship weapon as well. China is very keen to find out how well this works.
The AGM-88F, the version with anti-ship capability completed testing in 2014 and entered service. There had been so many new features in the F model that eventually the 88F got a new name; AARGM (Advanced Anti-Radiation Guided Missile) instead of a HARM. The older AGM-88s can easily be upgraded by simply replacing older sensors and guidance system components with new ones.
The AGM-88F has a GPS guidance added (with less accurate but jam-proof INS as a backup) added. The older AGM-88D also used GPS so that the missile, which normally homes in on radar transmissions, could be used to attack targets by location alone. The F model expands on basic GPS capabilities and also includes other features that assist in defeating enemy electronic defenses. What the GPS/INS provides is for a way for HARM to act on previous intelligence (about where an enemy radar is) while also using its radar signal homing capability and new anti-decoy features. Many countries now use a decoy emitter that send out a fake radar signal to lure the HARM away from the real radar. The 88F model uses GPS and more sensors and new software to get around all known deceptions (and some that haven’t been invented yet).
The first 88E production models were delivered in 2010 for testing on existing aircraft like the EA-18G, which entered service in 2011. AGM-88E testing ran into many problems in the three years before it entered service and there were more hardware failures than expected. The manufacturer admits that it is still working on some of these issues but that, in its current state, the AGM-88E is good to go.
The AGM-88 moves at high speed (2,200 kilometers an hour or 36 kilometers a minute). Over 24,000 AGM-88s, of all types, have been produced since the 1980s. AARGM weighs 361 kg (794 pounds) and can detect and attack targets more than 150 kilometers away while travelling at a speed of 2,450 kilometers per hour.
The AGM-88E can transmit a picture of the target, just before it is hit, so the user can be certain of what was taken out. The AARGM was developed jointly by U.S. and Italian firms. The original 1960s anti-radiation missile (ARM) quickly evolved into the HARM. Currently, there are orders for over 2,000 AGM-88E/Fs from the U.S. Navy and Marine Corps, Italy, and Germany.
The United States developed and began using anti-radiation missiles in the mid-1960s. The AGM-88 HARM entered service in 1985 as the AGM-88B and used passive radar seeker which home on enemy fire-control radars emissions in order to destroy it and thus render Surface-to-air missile (SAM) system useless (well at least those which use radars for target tracking). In 1999 (Kosovo War) HARM was found to be vulnerable. The Serbian forces limited their radar usage to minimum and used quick radar shutdown techniques and “pack and leave” tactic for their SAM units. Because of these HARM had problems with acquiring targets because the missile has precision guidance only when enemy radar is working during all the time (in “offline mode” missile uses INS/GPS only). As a result NATO forces failed to silence Serbian SAMs during the campaign.
China is apparently hoping to steal the new U.S. ARM technology and incorporate it into their various HARM missiles which must eventually be tested at sea to ensure that the anti-ship versions are working properly. If you know more about enemy HARM tech these systems are a lot less effective. This is especially true if you can keep secret how much you know. This the importance of ELINT, especially off the coast of foreign adversaries.