Russia has sent an S-400 missile battalion to its border with North Korea. This was announced as a precautionary measure, to protect Russian territory from the risk of one of the many North Korean missile tests going astray. The move also puts more pressure on North Korea to get its act together. The number of North Koreans fleeing into Russia is increasing, and Russia fears that a political collapse in North Korea would send over a million refugees flooding into Russia. Russia also wants to get the S-400 some free publicity, to assist efforts to obtain export sales.
It was only two years ago that the first S-400 battalion (eight launchers, each with four missiles, plus a control center and radar, around Moscow) officially became operational. A second battalion was deployed in the same area, later in 2007. The Russians claim that this new system can detect stealth aircraft, implying that the hypothetical enemy is the United States.
Russia also claims the S-400 can knock down short range ballistic missiles (those with a reentry speed of up to 5,000 meters a second, in the same way the similar U.S. Patriot system does.) S-400 has a longer range (at 400 kilometers) than Patriot (70 kilometers). Export efforts are hobbled by a lack of combat experience for the system. Patriot has knocked down aircraft and ballistic missiles, S-400 has not. Moreover, Russia anti-aircraft missile systems have a spotty history (especially when confronted by Western electronic countermeasures.) But Russia is already touting a new, S-500 system, that can knock down longer range ballistic missiles (with higher reentry speeds) and stealth aircraft. The missiles around Moscow are part of a project to rebuild the Soviet era air defense system, which has fallen apart since the early 1990s. The new system will be completed in about eight years. The S-500 will be available before that.