Why hasn't the US tried to stop the North Korean missiles?
The US has several anti-ballistic missile systems in South Korea and I think some more in Japan, so why haven't they tried to shoot down the North Korean missiles, like the one that North Korea just shot over Japan?
It seems to me that if a missile is flying towards a US ally with an unknown payload and unknown final destination, that the American military would want to shoot it down before it becomes a threat. If it is because they haven't had enough warning, then it seems like the US missile shields are total BS and wouldn't help in the event of actually needing them.
An missile capable of destroying the kind that overflew japan cost 10-20 million USD; and using it reveal a lot about your anti missile capabilities. It's expensive and counter productive.
I think I've read that shooting down a missile passing over its airspace would be incompatible with older interpretations of Article 9.
Note, if an entire country fires a single missile, the payload is known (no payload) and the final destination is known (the ocean). There was literally 0 chance that NK decided to start a surprise war by launching a single missile at Japan. If the launch of the missile was accompanied by dozens of other missiles, and literally millions of artillery shells towards Seoul, then Japan and/or the USA would have reacted.
Only touched upon in the answers is what a poor job "missile defense" systems do in actually intercepting missiles. Also something you don't want to advertise or emphasize in detail to the crazy dude with missiles.
Just a slight note: `like the one that they just shot over Japan` - on first reading, I thought "they = the Americans" (instead of "they = NK") and was very bewildered. You might want to fix that. ;)
@AndrewGrimm That relates to *Japan's* ability to shoot down a missile. The question is why didn't the *US* shoot down the missile.
The US didn't intervene because Japan was perfectly able to intercept the missiles and chose to not do it.
Japan’s J-Alert warning system advised people across a large area of northern Japan to seek shelter. Japan’s self-defence forces did not attempt to shoot down the missile and there were no reports of damage from falling debris.
The reason why Japan didn't intercept the missile was that they quickly measured its trajectory and concluded that it wouldn't hit them. I believe they preferred the missile to fall into the Pacific instead of having pieces of it raining on their cities.
EDIT: In response to a comment below doubting Japan's ability to intercept missiles, here is information about missile interception country by country, emphasis on the relevant part :
In 2016, the Japan Air Self Defense Force (JASDF), and also the Japan Ground Self Defense Force (JGSDF), initiated their 52nd year of annual live-fire missile launches at McGregor Range, New Mexico in Fort Bliss. The 2014 annual service practice of the PAC-3 Patriot missile demonstrated a 100 percent kill rate before a group which included the commanding generals of White Sands Missile Range (WSMR), and of the 32nd Army Air & Missile Defense Command (AAMDC). Every JASDF Patriot team participated in the annual exercise, which takes several months.
Since 1998, when North Korea launched a Taepodong-1 missile over northern Japan, the Japanese have been jointly developing a new surface-to-air interceptor known as the Patriot Advanced Capability 3 (PAC-3) with the US. So far tests have been successful, and there are planned 11 locations that the PAC-3 will be installed. A military spokesman said that tests had been done on two sites, one of them a business park in central Tokyo, and Ichigaya – a site not far from the Imperial Palace. Along with the PAC-3, Japan has installed the US-developed Aegis ship-based anti-ballistic missile system, which was tested successfully on 18 December 2007. The missile was launched from a Japanese warship, in partnership with the US Missile Defense Agency and destroyed a mock target launched from the coast
It seems a somewhat bold assertion to go from *"Japan's self-defence forces did not attempt to shoot down the missile"* to *"Japan was perfectly able to intercept the missiles"*. The former doesn't seem to imply the latter at all, and the article doesn't provide any further detail. Some additional sources might be helpful. What actually are Japan's abilities in shooting down missiles? It's worth considering that even the US's relatively advanced missile defence technology is not actually very effective, so I don't think "perfectly able" is going to be a good phrase regardless.
@JBentley If Japan wasn't able to intercept the missile, there would be no point for them or any other country involved to state that they didn't try. By the way, that your assertion that is bold. You provided no elements backing it and didn't seem to have bothered looking it up yourself either given how quickly I found relevant information.
@ksjohn Aegis as well as Patriot are not meant to take out ICBMs which are still midflight/in space, as was the case with the missile as it was flying over Japan. (See e.g. https://en.wikipedia.org/wiki/Missile_defense#Trajectory_phase) They are meant to take out warheads after they reentered the atmosphere. In this case, the ICBM was clear of Japanese territory by the time it did so.
@ksjohn Thank you for providing additional sources. I think you've got the wrong end of the stick about my comment though. It's not for me as a commenter to "look up" missing information in an answer. Its for you as the answerer to provide that information, and a commenter to point out that it is missing. Stack Exchange isn't about you or me, it's about all possible future readers.
@JBentley I wasn't criticizing you asking for references, which was quite legitimate. I was refering to your own unsubstanciated claims.
@ksjohn My claims are substantiated in the same article you linked, you were just selective about what you quoted. E.g.: "Additionally experts question the accuracy and reliability of these systems", and "Gruselle noted most French security experts doubted the technological feasibility of intercontinental ballistic missile defense". There is plenty of other material about the unreliability of missile defense systems out there if you want to pursue that line further.