On June 21, the U.S. Missile Defense Agency (MDA) and the Japan Ministry of Defense conducted a development intercept test of a new Standard Missile-3 (SM-3) Block IIA missile, an interceptor designed to operate as part of the Aegis Ballistic Missile Defense system. The missile failed to intercept the medium-range ballistic target missile. The reason for the failed intercept is not yet known, and details will not be available until test data can be reviewed.

The SM-3 Block IIA is being co-developed by the United States and Japan to defeat medium- and intermediate-range ballistic missiles. This was the fourth development flight test using an SM-3 IIA missile, and the second intercept test. The previous intercept test, conducted in February 2017, was successful.