美国有线新闻 CNN 日本东京首次针对他国发射导弹实施避难演习（在线收听）

For the first time since World War II ended in 1945, the Japanese capital of Tokyo held a drill that simulated a missile attack. Part of the drill, as you see here, was staged in an amusement park. It took about 10 minutes from start to finish, instructions came out through text messages and a loud speaker, and people who volunteered to participate moved quickly and calmly to some designated safe areas, most of those were underground.

Dozens of drills like this have been held across Japan in recent months. Like the U.S., Japan is a rival of North Korea, and Japanese Prime Minister Shinzo Abe says that the missile threat from North Korea has made the security situation in Japan the toughest since World War II.

Japan has been making large purchases of military equipment recently, mostly from the U.S. And critics are concerned that Japanese leaders might be working toward expanding the military beyond its role of self defense, and they accused the Japanese government of politicizing the threat from North Korea.

Japanese government officials say the two intercontinental ballistic missiles that North Korea fired over Japan last year are reasons why emergency drills are needed.

NICK PATON WALSH, CNN SENIOR INTERNATIONAL CORRESPONDENT: Nuclear weapons are terrifying devices, but much less of a threat until they are carried in a distance by a ballistic missile.

These ballistic missiles normally follow a curve. They fly into the air and follow and follow a predetermined trajectory until they hit a target.

This requires intense preparation and testing.

So, who has those and how can we defend against them?

Thirty-one countries are known to have ballistic missiles. Twenty-six have missiles that can travel at least 300 kilometers. And twelve are known to be able to reach a thousand kilometers.

Eight countries' missiles fa?ll into the last category, reaching at least 5,500 kilometers. These include ICBMs, intercontinental ballistic missiles, that can fly half-way around the world.

Now, these are just the missiles that we know about. There's an underground trade in some of this technology, traded illegally on the black market. That's thought to have happened after breakup of the Soviet Union. Iran has also been accused of providing missile technology to Houthi rebels in Yemen.

So, what can nations do to defend against them? The more they spread, the greater the focus on missile defense systems. Eighteen countries already have invested in some form of these vastly expensive systems, and five more are in the process of developing or purchasing them.

But that didn't solve the problem and it's unclear how effective they are. For instance, two countries that the U.S. sees as threats, North Korea and Iran, have far more missiles than the U.S. or any other country has interceptors. So, really, the U.S. or its allies need a strategy to deal with hostile missiles before they're even launched.