Repeated missile testing by North Korea in recent weeks has Japan on edge, opening up debate about revising its pacifist Constitution and putting the U.S.-Japan alliance in the strategic spotlight. Japan is particularly vulnerable to potential North Korean aggression. In early March, Pyongyang launched four ballistic missiles on the same day, three of which fell within 220 miles of Japan’s shoreline. Only last week the North tested yet another missile, although it exploded quickly after launching, making it Pyongyang’s third failed attempt in April. There are worries that a nuclear test may be in the offing. If so, it would be North Korea’s sixth in 11 years.

There is intelligence to suggest that North Korea now has the ability to manufacture both uranium and plutonium bombs. Pyongyang’s arsenal is estimated to comprise roughly 1,000 ballistic missiles and 10-20 nuclear warheads — most capable of reaching Japan.

Contingency measures

Last week’s failed test prompted the Tokyo Metro to shut down operations for about 10 minutes, a move that highlights just how jittery Japan is becoming. Municipalities across the archipelago are drawing up contingency measures to deal with a missile strike. Community alarm systems are being tested and evacuation drills practised. It’s estimated that Japan will have at the most about 10 minutes to warn its citizens in the event of an attack. Japan’s official civil defence website has been updated to explain notification measures and provide citizens with advice on how to react if attacked. The website had 5.7 million visitors in the first 23 days of April alone, compared with the usual monthly traffic of fewer than 400,000 hits.

But Pyongyang’s aggressive moves are also stirring up the always-swirling waters of the debate to revise the Japanese Constitution, in particular Article 9, a clause that outlaws war as a means to settle international disputes and restricts Japan’s ability to maintain a military deterrent. Prime Minister Shinzo Abe, a nationalist, stated this week he was confident a change to the Constitution would take place by 2020. But public opinion remains divided. A survey conducted by Kyodo News found 49% in favour of altering Article 9, with 47% against. Another poll by public broadcaster NHK found only 25% to be pro-revision.

Japan maintains a self-defence force of about 250,000 personnel with a defence budget of $44 billion, (in contrast, China’s military budget is $146 billion). North Korea’s missile tests have caused some lawmakers to call for Japan to increase its military spending and build a credible pre-emptive strike capability. Mr. Abe’s Liberal Democratic Party backs the introduction of advanced missile-defence equipment.

In the meantime, the U.S. is flexing its maritime muscles by sending Navy destroyers to hold joint exercises with Japan and South Korea. Washington is nervous that North Korea’s nuclear and missile capabilities might progress to the point where it could launch an attack on the U.S. soil directly. In a recent U.S.-Japan joint statement, President Donald Trump committed to “defend Japan through the full range of U.S. military capabilities, both nuclear and conventional”, somewhat allaying initial uncertainties over Mr. Trump’s isolationist outlook.

With North Korea showing scant signs of backing down, it remains difficult to know how the regional brinkmanship between the main actors, including Japan and the U.S., will actually play out.

But one of its clear effects is to bring the legal and technological basis for Japan’s pre-emptive capabilities into sharper focus.

Pallavi Aiyar is an author and journalist based in Tokyo.