Prime Minister Shinzo Abe's cabinet approved a plan Tuesday to buy two Aegis Ashore missile interceptor systems at a cost of almost $2 billion.
"North Korea's nuclear missile development poses a new level of threat to Japan and as we have done in the past we will ensure that we are able to defend ourselves with a drastic improvement in ballistic missile defence", Itsunori Onodera, the defence minister, said.
The two Aegis Ashore batteries, the land-based variant of the Aegis combat system, will strengthen Japanese defenses against China's and North Korea's growing ballistic and cruise missile arsenals.
The Defense Ministry estimates that the main Aegis Ashore units will cost slightly less than ¥100 billion each.
In case of failure, a second tier of missile defense will be involved to use the Patriot PAC-3 mobile ground-based systems that are supposed to intercept the missile at the final stage of its flight.
Japan's military planners also evaluated the US -built THAAD (Terminal High Altitude Area Defense) system before deciding on Aegis Ashore.
To accelerate the preparations for the deployment of missile defense complexes, the government intends to allocate 2.8 billion yen ($24 million) from the supplementary budget for the current financial year (ending March 31, 2018).
"We can not say what the final costs will be, but we will move ahead (to introduce Aegis Ashore) on the fastest possible schedule, given public calls that the government should deal as swiftly and urgently as possible with the ballistic missile defense issue", Onodera said. Therefore the government decided that Cabinet approval is necessary to introduce Aegis Ashore. It will be equipped with newly developed SM-3 Block 2A interceptors with enhanced defensive coverage and accuracy compared with the SM-3.
Support from local governments is indispensable for the operations of the Aegis Ashore system as its radars emit strong radio waves, possibly causing radio disturbance, sources familiar with the situations said.
North Korea has fired two missiles over Japan this year, as well as three intercontinental ballistic missiles on steep trajectories into the Sea of Japan.
"We believe this new system will significantly boost our abilities to deal with surprise attacks and saturation attacks", a ministry official said.