A ground-based interceptor missile fired from Vandenberg Air Force Base in southern California smashed into and destroyed a target launched from the Marshall Islands, the Missile Defense Agency announced today. This is the first test of the US homeland missile defense system against a “complex, threat­-representative [intercontinental ballistic missile] ICBM target," per the agency’s press release.

The test was meant to show that the US can defend itself against a missile attack using the ground-based midcourse defense system or GMD. It was also to try out an upgraded component of the system. The GMD system consists of sensors deployed around the world, at sea, and in space; they work together to detect a hostile missile launch, and track the missile as it flies. Then, in theory, the control centers in the US can use that information to guide an interceptor missile to knock into the enemy weapon while it’s still in space — away from people — and smash it into smithereens.

That’s how the GMD is supposed to work, anyway. In practice, only 10 of the 18 intercept tests have succeeded, including today’s. (And, actually, counting a 2006 test as a success is kind of controversial, because the interceptor hit the target, but didn’t kill it. Destroying the target, it turned out, wasn’t part of the test’s objectives.) An LA Times investigation also reported that a January 2016 flight test considered successful in fact experienced a thruster malfunction, “causing the interceptor to fly far off-course.” The MDA says they dispute that characterization.

So: though the Missile Defense Agency is saying today is a success, that success may be asterisked. And they’re still evaluating the results. Still, the test is a step towards demonstrating the system is capable of protecting the US against a small-scale ICBM attack — like one that North Korea could one day be capable of launching. But neither North Korea, nor our missile defenses, are ready for action. For example, since it could take several interceptors to destroy an enemy’s warhead, the GMD still needs to be tested in a situation where multiple interceptors are fired together. But that’s not planned until late 2017 or 2018 per the Government Accountability Office, so stay tuned.