What kind of anti-missile defences does the US possess?
The US has various anti-missile options, some designed to take down missiles at short-range and others for medium-to-long-range. The US relies heavily on the US Patriot missile and the Terminal High-Altitude Area Defence (THAAD). The US deployed THAAD to South Korea this year to defend against medium-range missiles. There is a three-phased defence system: ground-based missiles on the Korean peninsula; US naval ships stationed in the Pacific; and two bases in Alaska and California that can launch an estimated 36 interceptors.
Is the US system robust enough to stop a North Korean missile attack?
No air defence system offers anything like a complete guarantee of success. The Pentagon offer repeated assurances that air defence systems would be more than a match for any North Korean attack. But when missile defence systems have been put to the test over the last few decades, the performance has been far from reassuring.
The US provided anti-missile defence systems to Israel and Saudi Arabia during the First Gulf War as protection against Iraq's Scud missiles. It was initially claimed that they had shot down 41 of 42 missiles fired by Iraq. But eventually it was acknowledged that only a few missiles had been hit.
Recent tests of interceptors have provided little comfort – with success rates of around 50% on average. The Pentagon celebrated in May when it destroyed a mock warhead over the Pacific but overall the performance has been spotty. Since the newest intercept system was introduced in 2004 only four of nine intercept attempts have been successful. Of the five tests since 2010, only two have been successful.
Source: The Guardian (UK)