Japanese officials have acknowledged that they miscalculated the elevation angles of various mountains when deciding where to base one of their two future Aegis Ashore missile defense systems. This led them to identify the only suitable location in Eastern Japan was the Araya maneuver area, although nine others may have been viable.

Takashi Gomi, in charge of the Japanese Ministry of Defense’s strategy planning division, disclosed the error to reporters during a press conference in the city of Akita on June 10, 2019. The Japan Ground Self Defense Force’s (JGSDF) Araya Maneuver Area, which already hosts Patriot surface-to-air missile systems, is situated in Akita. In January 2019, Japan’s Ministry of Defense had announced that it would conduct a review of the planned Aegis Ashore site’s environmental and health impacts, stemming from concerns from local officials and residents about possible negative effects of electromagnetic radiation from the system’s powerful Long Range Discrimination Radar (LRDR) radar. Japan’s Aegis Ashore sites will use the LRDR in place of the original system’s AN/SPY-1 radar.

Confusion about the scale of the transformation when using Google Earth’s three-dimensional virtual globe feature has led officials to misinterpret the elevation angle of some mountains by more than 10 degrees in some cases, according to Gomi. The Japanese Ministry of defense laid out a requirement to base the two Aegis Ashore systems on areas where there were no obstacles with elevation angles greater than 10 degrees at a certain distance.

Members of the press watch as trucks linked to Patriot surface-to-air missile systems (Patriot surface-to-Air missile systems) arrive in the Araya maneuver area amid a wave of North Korean missile launches in 2009.

The problem here is the need to provide a good line of sight for the LRDR to be able to detect and track targets in order to cue the SM-3 interceptors of the Aegis Ashore system. If the radar does not have a clear view, it can limit the time between detecting a threat and engaging it. 

Over time, this may become a less important issue. On December 11, 2018, the U.S. military successfully conducted the first ever test of the Aegis missile defense system (ABM), using the so-called “remote” concept of operations. That means off-Board sensors spotted and tracked the target, and then provided firefighting quality control data to the interceptor launch site. Japan could in the future network Aegis Ashore sites in the future along with other radars and sensors, on land and at sea, including the Japanese Maritime self-defense force Aegis BMD equipped with 27DDG destroyers.

A briefing slide describing the various components of the Aegis Ashore system, as well as various interaction options, including threat targeting using off-Board sensors.

“We can study the numbers as long as we have data maps,” Gomi said, defending Japan’s defense Ministry’s decision not to conduct physical site studies of these potential obstacles. “Our verification system was insufficient.”

Despite admitting the error, Japanese authorities have no plans to review any of the nine other potentially usable sites. Gomi gave no explanation as to why this was the case, according to Japanese newspaper The Mainichi Shimbun. This could come as a shock to local authorities, who have already said they received little information about how Araya was chosen in the first place.

Gomi also did not say whether there were similar errors in deciding the location of the second aegis Ashore site in the Mutsumi maneuver area of the JGSDF, which occupies areas in the cities of Hagi and Abu in Western Japan. The Japanese government approved the aegis Ashore plan in December 2017, and the U.S. government approved the planned sale of essential components, ancillary goods and related services for a total of about $2.15 billion in January 2019. Japan’s goal is to have both facilities operational by 2023, and it is no doubt keen to avoid any delays in that schedule.

Aegis Ashore missile defense test facility in Kauai, Hawaii. The Japanese aegis Ashore objects will be similar, but in particular will be different from the radar that can be seen here.

It is certainly true that Japan has moved forward very quickly with its Aegis Ashore procurement, primarily due to the growing threats from North Korea. Despite a long pause in North Korean missile launches amid a thaw in relations with Korea and the United States, the regime in Pyongyang recently resumed testing short-range ballistic missiles. North Korea also has a long history of test-firing missiles and sending them either flying in the East China sea that separates the two countries or even across Japan’s home Islands in the Pacific.

Aegis Ashore will also provide Japan with a broader regional missile shield that could help protect remote areas, including the Senkaku Islands, which are at the center of a long-running and increasingly hostile territorial dispute with China. There is also the possibility that Aegis Ashore facilities could evolve into a more offensive ground weapons system with the addition of SM-6 multipurpose missiles or Tomahawk ground attack missiles instead of SM-3. 

The U.S. government claims that Aegis Ashore is incapable of accepting the Tomahawk, a decision it took to ensure compliance with the now-defunct Intermediate-Range Nuclear Forces Treaty, or INF, with Russia. But Aegis Ashore uses a version of the Mk 41 Vertical Launch System, other variants of which are found on various ships in the U.S. Navy and other navies around the world and can accept these missiles. It remains a matter of contention between U.S. and Russian authorities about how difficult it would be to convert the land-based version to use other missiles beyond the SM-3. A clear offensive capability could also run afoul of Japan’s pacifist constitution, though there has been a growing push in the country to revise Article Nine, which prohibits non-defensive military activities.

A U.S. Navy briefing slide showing common components found on variants of the mk 41 Vertical Launch System, including the version that Aegis Ashore uses.

Depending on the exact specifications of the lrdr version Japan will use for its Aegis Ashore sites, the radar may also have a secondary intelligence gathering role. China has previously criticized the deployment by the U.S. military of AN/TPY-2 radars linked to the missile defense system (THAAD) in the area of the high-altitude terminal (THAAD) in both Japan and Korea. Chinese authorities have expressed concern that it could be used to spy on activities on its territory, although it is unclear whether the radar has that capability. 

In any case, the Japanese government seems adamant about building a ground-level missile defense within the next four years. It remains to be seen whether the miscalculation that led to the selection of the Akita site will have any significant impact on these plans, providing additional fuel to existing opposition from local officials or the public. 

But, if nothing else, one can imagine that the Japanese defense Ministry will make sure to triple-check their math when looking at potential locations for any major new military installations in the future.

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