The move risks angering China, locked in a dispute with Japan over nearby islands which they both claim.
Defense Minister Itsunori Onodera, who attended a ceremony on Yonaguni island to mark the start of construction, suggested the military presence could be enlarged to other islands in the seas southwest of Japan’s main islands.
“This is the first deployment since the U.S. returned Okinawa (1972) and calls for us to be more on guard are growing,” Onodera told reporters. “I want to build an operation able to properly defend islands that are part of Japan’s territory.”
The military radar station on Yonaguni, part of a longstanding plan to improve defense and surveillance, gives Japan a lookout just 150 km from the Diaoyu islands.
Building the base could extend Japanese monitoring to the Chinese mainland and track Chinese ships and aircraft circling the disputed crag.
The 30-sq-km Yonanguni is home to 1,500 people and known for strong rice liquor, cattle, sugar cane and scuba diving. Prime Minister Shinzo Abe’s decision to put troops there shows Japan’s concerns about the vulnerability of its thousands of islands and the perceived threat from China.
The new base “should give Japan the ability to expand surveillance to near the Chinese mainland,” said Heigo Sato, a professor at Takushoku University and a former researcher at the Defense Ministry’s National Institute for Defense Studies.
“It will allow early warning of missiles and supplement the monitoring of Chinese military movements.”
Japan does not specify an exact enemy when discussing its defense strategy but it makes no secret it perceives China generally as a threat as it becomes an Asian power that could one day rival Japan’s ally in the region, the United States.
Japan, in its National Defense Program Guidelines issued in December, expressed “great concern” over China’s military buildup and “attempts to change the status quo by coercion” in the sea and air.
China’s decision last year to establish an air-defense identification zone in the East China Sea, including the skies above the disputed Diaoyu islets, further rattled Tokyo.

Tapping concern about China, Abe raised military spending last fiscal year for the first time in 11 years to help bolster Japan’s capability to fight for islands with a new marine unit, more longer-range aircraft, amphibious assault vehicles and helicopter carriers. Japan’s thousands of islands give it nearly 30,000 km of coastline to defend.
Onodera’s groundbreaking ceremony on Yonaguni took place four days before President Barack Obama lands in Tokyo for a summit with Abe, the first state visit by a U.S. president in 18 years.