Remember the DF-21 China used to shoot down its satellite? Well, the ballistic missile has other uses as well. The missiles are designed to zoom into space and then rain down on U.S. bases or moving ships, such as aircraft carriers, as far as 900 miles from their launch sites -- hence the nickname "carrier killer" and the reason that the United States is sending many of its ballistic missile defense ships to the Pacific. China has been building a fleet of the missiles that is thought to have become operational in 2009 or 2010. And it is fielding the DF-21D in conjunction with a host of advanced radars, surveillance drones, spy satellites, and so-called triple-digit surface-to-air missiles designed by Russia that are capable of shooting down most U.S. aircraft. All of these systems are part of China's "area denial" strategy, aimed at keeping enemy ships and aircraft far from its shores.