Newsbeat guide... US missile defences in North Korea

The Americans have reacted to North Korean nuclear threats by deploying missile defence systems, but what are they?

The defences have the capability to shoot down missiles from both inner space and the inner atmosphere.

These missile defences are placed anywhere that is a possible target, like the island of Guam 2000 miles off the North Korean coast.

There are three systems working together to stop a missile:

Aegis BMD (ballistic missile defence) to stop the missile in space.

THAAD (Terminal High Altitude Area Defence) to shoot the missile as it leaves space.

Patriot, to destroy the missile as it nears its target.

The patriot missile and the US Aegis system were tested in 2011 in an exercise called Rapid Arrow, according to a NATO spokesman the systems worked well.

The Ballistic Missile Destroyer

The first Aegis, or the ballistic missile destroyer is based on ships, two of the missile defence ships have been moved off the coast of South Korea.

BMD fires from USS Hopper
This is guided by satellites to stop the missile whilst still in space

This is fired straight up to hit the missile before it enters the atmosphere, stopping it well before there is any danger of causing any damage.

The THAAD

The next stage is THAAD or terminal high altitude area defence, these are guided to the missile by radar hitting it at twice the speed of a bullet whilst still in the upper atmosphere.

a THAAD launcher waits to fire
The THAAD missile is moving to Guam however can only protect the area it is stationed in

They have no explosive and simply knock the ballistic missile out of the sky, destroying it but making sure the nuclear weapon doesn't explode.

The Patriot

The final stage is Patriot. This is when the only choice is to stop the weapon at close range, about 15 miles high, these can hit any kind of missile or aircraft.

Patriot missile firing
The Patriot missile is widely available and are also on the two US ships off the coast of South Korea

These either hit or explode near the missile to stop a nuclear detonation and keep it far enough away. These defences are very accurate with a high success rate.