As urged by U.S. President Donald Trump, Japan is accelerating efforts to beef up its defenses against North Korea, but Tokyo is likely to encounter technological and budgetary limits when expanding its role in the bilateral security alliance.

During a telephone call with Prime Minister Shinzo Abe on July 31, Trump showed frustration with Japan’s defense-only security policy, which limits its efforts to contribute militarily to the stability of East Asia, according to diplomatic sources.

In a joint statement issued after “two-plus-two” security talks in Washington on Aug. 17, Japan expressed an intention to boost its role in the bilateral alliance. The meeting was attended by Foreign Minister Taro Kono and Defense Minister Itsunori Onodera, and U.S. State Secretary Rex Tillerson and Defense Secretary James Mattis.

“Japan intends to expand its role in the alliance and augment its defense capabilities, with an eye on the next planning period for its Mid-Term Defense Program,” the statement said.

The ministers instructed their officials to “explore new and expanded activities in various areas,” made viable by the publicly divisive security laws Japan enacted last year, it said.

At the meeting, the Japanese ministers notified their U.S. counterparts of plans to introduce the U.S.-developed Aegis Ashore missile defense system to counter North Korea’s intermediate-range ballistic missiles. Japan’s current missile countermeasures comprise the Standard Missile-3 interceptors fired from Aegis-equipped destroyers and ground-based Patriot Advanced Capability-3 missile batteries.

But the Maritime Self-Defense Force has only four Aegis destroyers available at the moment, and each PAC-3 battery’s range of coverage is limited to tens of kilometers.

Just two units of the Aegis Ashore system, meanwhile, are seen as capable of covering Japan in its entirety.

Nonetheless, a hit probability of 100 percent cannot be expected from the interceptors, and North Korea is improving its ability to conduct a saturation attack that could overwhelm Japan’s defensive capabilities.

Some analysts say North Korea is now able to fire 200 missiles simultaneously at Japan.

“It’s not like we can shoot down every missile even after the new equipment is introduced,” a senior Defense Ministry official said.

Japan’s bid to enlarge its role in its alliance with the U.S. may also face economic problems.

Aegis Ashore is cheaper than the U.S. Terminal High Altitude Area Defense system, another option considered by Japan.

Aegis Ashore batteries cost ¥80 billion each and two would be enough to cover Japan. Using THAAD, however, would require at least six batteries costing over ¥100 billion each to cover the same area.

At the same time, the cost of developing a pre-emptive strike capability for North Korea could also cause Japanese defense spending to surge.

Within the government, at least, there have been no specific discussions on the politically sensitive issue. But doing so would require Japan to buy even more equipment, such as more fighters and precision-guided bombs.

In the two-plus-two statement, the ministers pledged to “pursue additional types of cooperation” under the security laws, which expanded the scope of what the Self-Defense Forces can do overseas. This phrase suggests the SDF’s duties could expand.

“The people would now accept this amid elevated tensions over North Korea,” a senior official in the Foreign Ministry argued.

But according to recent media polls, less than 20 percent of the Japanese people consider a hike in defense spending acceptable.

Abe is believed eager to restore public trust in his administration via diplomatic and economic achievements. It is not clear, however, that his team will benefit from a defense buildup that takes advantage of the regional tensions building over North Korea.

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