The North Koreans haven't had much luck with testing their long range, ICBM. Twice they've had to destroy the missile shortly after liftoff, although the last attempt successfully launched a satellite into space.

But that doesn't mean they eventually won't stumble on to a solution and perfect a missile that could hit most of the West Coast. And that's why the Pentagon is spending a billion dollars to deploy additional anti-missile interceptors.

New York Times:

The new deployments, announced by Defense Secretary Chuck Hagel on Friday, will increase the number of ground-based interceptors in California and Alaska to 44 from 30 by 2017.

The missiles have a mixed record in testing, hitting dummy targets just 50 percent of the time, but officials said Friday's announcement was intended not merely to present a credible deterrence to the North's limited intercontinental ballistic missile arsenal. They said it is also meant to show South Korea and Japan that the United States is willing to commit resources to deterring the North and, at the same time, warn Beijing that it must restrain its ally or face an expanding American military focus on Asia.

"There's been a quickening pace of provocations," said one senior administration official, describing actions and words from North Korea and its new leader, Mr. Kim. "But the real accelerant was the fact that the North Koreans seemed more unmoored from their Chinese handlers than even we had feared."

Although American and South Korean intelligence officials doubt the North is close to being able to follow through on a nuclear strike, or that it would even try, given its almost certain destruction, analysts say the country's aggressive behavior is an important and worrying sign of changing calculations in the North.

In interviews over recent days, Obama administration officials described internal debates at the White House and the Pentagon about how strongly to react to the recent provocations. It is a delicate balance, they said, of defending against real potential threats while avoiding giving the North Koreans what one official called "the satisfaction of seeming to make the rest of the world jumpy." 

Missile defense technology is still in its early stages of development and many Pentagon anaylsts are worried at the reliability of the interceptors. It's one thing to shoot down a Scud, and an entirely different matter to hit a warhead descending from space. But the technology is progressing and the interceptors are getting more accurate all the time.

The Pentagon is still contemplating putting missile defense on the east coast to defend against an Iranian missile. The Iranians are even further behind in developing a long range rocket so that decision can be put off for the time being.