How long do people in Japan have to react to a North Korean missile launch? Virtually no time at all.

The Japanese government says Tuesday’s North Korean missile was launched at 05:58 Japan time, before flying over Japanese territory and landing in the sea east of Hokkaido at 06:12.

The government issued a text alert to citizens at 06:02, warning them that a missile had been launched and advising them to evacuate to a “sturdy building or basement”.

The missile was only over Japanese territory (land as opposed to sea) for a few minutes – between about 06:05 and 06:07 according to the national broadcaster, NHK.

In other words, if the missile had actually been aimed at a Japanese target there could have been as little as three minutes between the first warning and a potential impact.

Not enough time for the majority of people to get to safety.

Missile defence

So defensive measures become extremely important.

What does Japan have at the moment, and what else could it get?

The current missile defence system comes in two stages.

There is the Aegis system, which is deployed on Japanese, US and South Korean naval craft in the region. It is designed to intercept missiles in early or mid-flight.

Then there are a number of short-range Patriot anti-missile batteries (PAC-3) deployed in Japan. They are designed to shoot down missiles as they descend towards their target.

It’s not a bad combination, but for the Aegis system your ships have to be in the right place at the right time for intercept to be possible.

And while the Patriot system can provide effective defence for specific locations, it is less effective if it needs to defend a wide area.

There are alternatives, but they are expensive and would take time to install.

Japan could invest in a land-based Aegis system which would provide extra security. Or it could consider an extra layer of defence such as the Terminal High-Altitude Area Defence (THAAD) system, which has been deployed in Guam and supplied by the US to South Korea.

The THAAD system is not really battle-tested, however.

The trouble is that none of these defence systems would provide guaranteed protection against a barrage of missiles, fired unexpectedly.

That’s why there has been debate in the Japanese defence establishment about acquiring advanced systems that would allow Japan to destroy North Korean missiles either on the point of launch or even pre-emptively.

It is not clear, though, whether this would be permissible under Japan’s pacifist constitution. Source.