TOKYO -- Japan aims to have U.S.-developed Aegis Ashore missile defense systems up and running by fiscal 2023 to counter growing North Korean threats, but the costly technology may still fall short in providing full protection to the country.

The cabinet Tuesday voted to procure two Aegis Ashore systems, to be placed at Self-Defense Forces bases in northern Akita Prefecture and southern Yamaguchi Prefecture to cover Japan's entire territory. Land surveys and construction will take about five years, meaning actual operations would start around fiscal 2023.

In hopes of speeding up the timeline, the government will incorporate financial assistance from the U.S. military in a supplementary budget to be approved by cabinet Friday.

The Japanese Defense Ministry estimates each of the systems, including related facilities, will cost around 100 billion yen ($885 million).

Japan currently has a two-pronged missile defense system: the Maritime Self-Defense Forces' Aegis-equipped destroyers, and the Air SDF's Patriot Advanced Capability-3 missiles. The land-based Aegis Ashore will be operated by the Ground SDF, creating a network that involves all three branches of the Japanese forces.

The Aegis Ashore systems will be armed with SM-3 Block IIA interceptor missiles, which are being developed jointly by Japan and the U.S. for deployment starting in fiscal 2021. They have greater thrust than the SM-3s currently used by Aegis-equipped vessels, and also a greater operational altitude exceeding 1,000km.

Improving accuracy remains a concern. North Korea last month launched an intercontinental ballistic missile on a lofted trajectory, which reached an altitude of about 4,400km. Rockets on this type of trajectory "are very difficult to shoot down, even with Aegis Ashore's advanced missile detection and tracking capabilities," said a Defense Ministry official.

North Korea also succeeded in simultaneously firing four midrange ballistic missiles in March. In order to intercept them all, Japan would have had to instantly calculate each of their trajectories and targets. But doubts remain on the accuracy of the SM-3 Block IIA, which hit its target in a February test but missed in June.

The Aegis Ashore has its limits, so Tokyo also plans to upgrade other components to bolster its overall defenses. It will overhaul an SDF system used to predict missile targets and instruct an intercept, as well as a new radar to track incoming rockets.

These updates will come with a massive price tag. The Japanese government has spent 1.84 trillion yen on missile defenses since fiscal 2004. The tally is expected to surpass 2 trillion yen next fiscal year.

The Aegis Ashore will be budgeted in fiscal 2019 and beyond. The systems could end up costing more than the current estimate of 200 million yen combined if they are equipped with better radars.

Procurement of the Aegis Ashore systems, made by America's Lockheed Martin, is likely to come under the U.S. government's Foreign Military Sales framework. This gives the U.S. the upper hand in terms of pricing and delivery date, and will make it hard for Japan to negotiate on the price or for installment payments.

Japan's decision on the Aegis Ashore threatens a backlash from China and Russia, which keep a close eye on Tokyo's defensive capabilities. Valery Gerasimov, chief of the general staff of the Russian forces, met with Japanese Defense Minister Itsunori Onodera on Dec. 11 and expressed concerns that the U.S. will be involved in the operation of the missile defense system.

(Nikkei)