The U.S. Navy believes that China has already begun deploying the DF-21D ballistic missile, which was designed for use against the U.S. Navy, particularly aircraft carriers. In response, the Americans are developing defenses and countermeasures against the DF-21D. Details of this effort are, for obvious reasons, kept secret.
The basic DF-21 is a 15 ton, two stage, solid fuel missile that is 10.7 meters (35 feet) long and 140cm (4.6 feet) in diameter. Range varies (from 1,700-3,000 kilometers) depending on model. The DF-21D is believed to have a range of 1,500-2,000 kilometers. While the 500-2,000 kg (.5-2 ton) warhead usually contains a nuclear weapon, there are also several types of conventional warheads, including one designed for use against warships. Some of these conventional warheads are for use against targets in Taiwan. This is because the DF-21, as a longer range ballistic missile that comes down on the target faster than the 1,200 shorter range ballistic missiles aimed at Taiwan. That means that the DS-21 is too fast for the Pac-3 anti-missile missiles Taiwan is installing around crucial installations.
Until recently, there was no evidence that the complete DF-21D system had been tested. But recently satellite photos showed a 200 meter long white rectangle in the Gobi Desert (in Western China) with two large craters in it. This would appear to be a “target” for testing the DF-21D, and two of the inert practice warheads appear to have hit the target. American carriers are over 300 meters long, although the smaller carriers (amphibious ships with helicopter decks) are closer to 200 meters long. It appears China is planning on using the DF-21D against smaller warships, or perhaps they just wanted to see exactly how accurate the missile could be.
Over the last three years various components of the DF-21D were tested, but until these satellite photos showed up there was no evidence that there had been any tests of the complete system against a carrier size target. In the last two years there have been photos of DF-21Ds on TELs (transporter erector launcher vehicles), and announcements of the first units activated three years ago. Now we have the tests. What has not been tested, apparently, is a “dress rehearsal” test against a large ship (an old tanker or container ship would do) at sea and moving. That might yet happen.
Meanwhile, China has three "remote sensing" satellites in orbit, moving in formation at an altitude of 600 kilometers across the Pacific. Equipped with either radar (SAR or synthetic aperture radar) or digital cameras, these three birds can scan the ocean for ships, even though the Chinese say their purpose is purely scientific. A typical SAR can produce photo quality images at different resolutions. At medium resolution (3 meters) the radar covers an area 40x40 kilometers. Low resolution (20 meters) covers 100x100 kilometers. This three satellite Chinese posse looks suspiciously like a military ocean surveillance system. This is the missing link for the Chinese ballistic missile system designed to attack American aircraft carriers.
China has been developing the DF-21D for about a decade. Most of the development effort was devoted to targeting systems that would enable them to seek out and find aircraft carriers. On the DF-21D warhead itself, sensors would use infrared (heat seeking) technology for their final approach. This sort of thing had been discussed for decades, but China appears to have put together tactics, sensors, and missile systems that can make this all happen. The key was having multiple sensor systems which would include satellites, submarines, or maritime patrol aircraft that could find the general location of the carrier before launching the ballistic missile. Those sensors appear to be operational, as is the DF-21D itself.
The Chinese Second Artillery Force (sometimes called Corps) operates all land based long range ballistic missiles. Its units operate over several provinces it has been expanding over the last few years. This includes adding two brigades armed with theDF-21D. This gives the Second Artillery Force ten DF-21 brigades, plus brigades with several other types of missiles. Each of the DF-21 missile brigades has six missile battalions (with two mobile launchers each), two maintenance and repair battalions, a site management battalion, a signal battalion, and an electronic countermeasures (ECM) battalion. The other eight DF-21 brigades in the Second Artillery Corps are the older models.