The US Defense Department's Defense Security Cooperation Agency (DSCA) announced on December 9 that the US government plans to allow the sale of four Raytheon Standard SM-3 Block IIA missiles and compatible Mk 29 launch canisters from BAE Systems to Japan. The estimated cost will be $133.3 million. The US State Department has approved the sale, and the DSCA has notified Congress of the pending sale.

The SM-3 Block IIA is the latest version of the US Navy's air defense missile, used by ships equipped with the Aegis Ballistic Missile Defense (Aegis BMD) system. The missiles can potentially be used to shoot down ballistic missiles in flight, even outside the Earth's atmosphere. In theory, the new missiles would give Japan a better shot at shooting down a ballistic missile arcing over Japan.

The sale comes on the heels of the Japanese National Diet's approval of a plan to build an Aegis Ashore missile defense system (the National Diet is Japan's parliamentary-style bicameral legislature). That system would be based on the land-based missile defense facilities the US Navy has deployed in Romania and is preparing to activate in Poland. Japan's only current land-based ballistic missile defense is the Patriot system, including Patriot Advanced Capability 3 missiles—and the PAC-3 is more of a point defense system, with much shorter range.

At sea, Japan has previously deployed the SM-3 Block IB—a missile with a range of more than 700 km (380 miles)—aboard the Japanese Maritime Self Defense Force's (JMSDF's) Aegis-capable destroyers. By comparison, the Block IIA has a range of 2,500 km, or 1,350 miles. The extended range would allow for a higher probability of an intercept of a North Korean missile—and a few moments more to respond, as it would slightly expand the window for a shoot-down (but just slightly). It would also allow Japan to defend against North Korean missiles without deploying Aegis-capable launch ships close to North Korean waters.

Additionally, the missile sale and the required integration work associated with the deployment will improve the JMSDF's interoperability with US missile defense systems, allowing the JMSDF to integrate with the US Navy in defense of US installations in the Western Pacific—including Guam, which is in range of North Korean intermediate-range ballistic missiles.