Japan's three tiered anti-missile defense program. The main threat is nuclear tipped ballistic missiles from North Korea and to a lesser extent China. Japan hasn't decided whether it will, or can, deploy the third tier (known as THAAD). (Diagram courtesy Asahi Shimbun)
We in Australia have no idea how serious the conventional and especially nuclear threats are to Japan. Threats to Japan are a major reason why yesterday's Japan-Australia talks featured regional security so highly.
The nuclear missiles (without their warheads) that North Korea has tested for years near Japan are causing greater Japanese anxiety.
- one reason is that North Korea has been steadily shrinking formerly too large nuclear warheads to a
small enough size to fit on missiles.
- another reason is North Korea is developing submarines that could fire nuclear missiles.
China has a much more mature and powerful nuclear arsenal than North Korea. China has had missile warhead sized nuclear weapons since the 1960s and submarine fired nuclear missiles since the 1980s.
A North Korean or Chinese nuclear missile could reach Japan in under 5 minutes - hence Japan is worried.
To meet these threats Japan is developing increasingly comprehensive anti-missile missile defenses to shoot down North Korean and also Chinese missiles.
RYO AIBARA for Japan’s Asahi Shimbun, January 14, 2017, reports http://www.asahi.com/ajw/articles/AJ201701140038.html
“...Japan currently relies on a two-pronged approach for missile defense, but is considering adding a third element because of the rapid advances in missile technology by North Korea.
...Japan's current missile defense involves a two-tiered system.
Outside of the atmosphere, SM-3 interceptor rockets launched by Aegis vessels would target ballistic missiles, while surface-to-air [Patriot] PAC-3 missiles would be aimed at the ballistic missiles once they re-enter the atmosphere.
Based on the Medium-term [Japanese] Defense Program for the period from fiscal 2014 until fiscal 2018, the number of Aegis destroyers capable of carrying SM-3 rockets will double from the current four. Improvements will also be made on the SM-3 and PAC-3 missiles to expand the range over which they can shoot down ballistic missiles.
[there are also calls in Japan for a third system]...the [Terminal High Altitude Area Defense (THAAD)] system...capable of intercepting missiles moving at far higher trajectories and even outer space.
...A major hurdle for deploying the THAAD is cost. Putting the system into play would require hundreds of billions of yen [many US$ Billions], which may be beyond what the [Japanese] Finance Ministry would sanction given the nation's tight fiscal crunch.