Well, the intercept worked. Which shouldn't have been that surprising, despite what some arms control wonks thought (you know who you are...).
Details here: a single RIM 161 SM 3 mod was fired, intercepted the satellite at 153 miles altitude with a closing speed of 17k mph. Pretty damn close to the proverbial BB-hitting-a-bullet and a tribute to good old American engineering. More on the missile here: it is based on a SM2 Block IV missile with an additional third stage, guidance and warhead technologies. It is a follow-on system from Terrier LEAP of 1992.
So, what are the implications of this successful intercept - and I'm not going to get into whether this was a hidden test or not, that's for the folks who pretend that such things matter - and what does it mean?
First of all, it changes the status of any US ship capable of firing the SM 3 mod missile, from "mere" warship to anti-ballistic missile capable warship. This is a huge, huge change: it means that the capabilities of the US Navy have expanded enormously, giving them the ability not merely to defend against aerial attack, but also against missile attacks that were, up to now, considered invulnerable. There was no way, to date, to attack a ballistic missile once it was fired and had passed the boost phase (theoretically, you could use a conventional antiaircraft system to attack during the boost phase if you were within range; alternatively, you could use fighter aircraft to attack directly during the boost phase as well. But until this test, a potential enemy could place their missiles well out of range during the boost phase and you couldn't defend against them, just hunker down and hope for the best.
No longer: intercepting a ballistic missile with the SM-3 mod is now eminently feasible, unless, of course there are active measures involved from the ballistic missile, such as decoys and/or manouevering, and even then there'd be a very good chance of intercept, even from a single missile fired at the target.
This means that you can defend against ballistic missile attack on a tactical level: all you need is a US warship capable of firing the SM-3 mod.
Now, what are the implications of this?
One scenario for a US-Chinese conflict is a massive attack by the PRC against Taiwan over the Taiwanese Straights, which would entail heavy use of ballistic missiles to knock out the majority of Taiwanese air assets to prevent a massacre as the PRC transports troops to force a landing. If the PRC fails, they will lose the vast majority of their troops and the attack would fail. Further, given that the US would come to Taiwan's aid in the case of such an attack, the Chinese have invested heavily into medium-range, non-nuclear ballistic missiles to attack not only Taiwan, but also US carriers coming to Taiwan's aid: while Chine might have to fire 30 such missiles to get a hit, that is, for them, an excellent neutralization of the threat of US carriers (and it is a massive threat to such a landing attempt). China has put in some 800 medium and short-range missiles in and around the Taiwanese Straights for this purpose.
Basically, the Chinese plan was to identify a rough area of where the carrier and support ships would be, within a 5 square mile area, and then fire enough missiles to saturate that area within a very short period of time, forcing the US either to break off and run or face severe damage from such an attack, with a very decent probability of sinking not only a carrier, but most of the support ships in the task force as well.
Now this alternative has been, largely, removed. Being able to fire the SM-3 mod, support ships could destroy only those missiles that would actually come close to hitting US ships, enabling them to continue operations.
This means that the US interception now has created a great deal of uncertainty with Chinese planners: they cannot count on being able to take out a carrier and most of its support ships. They can continue to engage such ships, but unless they can destroy them or put them out of commission - kinetics alone would be damaging, let alone a conventional warhead - then the costs to the Chinese will be enormous in terms of US ability to destroy their invasion force.
It goes, of course, much further: if any ship capable of firing a SM-3 mod is also capable of intercepting a ballistic missile, that means that certain horror scenarios - of, say, Iran firing an IRBM from a freighter off the Eastern seaboard - can be called into question: instead of merely having to execute such a plan, now such a country would have to also know where such warships were to ensure that they are out of range, and this exceeds the abilities of such a country by quite a large margin - are no longer feasible.
That's deterrence as well.
Further, it disrupts any opponents' ability to use space-born assets with impunity for reconnaissance in wartime: they can be brought down, and without great effort. Just move the ship, charge up a SM-3 mod and move the ship to intercept: as far as these things go, fairly trivial, as has been proven.
That's deterrence as well.
The implications are severe: the US, basically, has proven to now possess a working anti-ballistic missile defense that has shown itself capable of working under real-world conditions.
For the US and their allies, that's good news: it is very, very bad news for anyone planning a war against the US and their allies.
And that is deterrence.
Oh, and what ships can fire this? Anything with an Aegis system.
Expect significant orders from both Japan and Taiwan...