Japan's territorial row with China over the Senkaku Islands entered a heightened phase of tension with Tokyo's Feb. 5 announcement that a Chinese warship directed fire-control radar on a Japanese destroyer in the East China Sea in January, military experts say.
"I find it very regrettable that China behaved in such a provocative one-sided manner, given the signs for dialogue in both Japan and China," Prime Minister Shinzo Abe said at an Upper House plenary session on Feb. 6, referring to the development.
He accused the Chinese military of engaging in "dangerous acts that could trigger an unforeseeable crisis."
"We filed a protest with China via diplomatic channels and pressed Beijing to prevent a recurrence," he said. "I strongly call on China to return to the starting point of a 'mutually beneficial relationship based on common strategic interests' and to exercise self-control so as not to escalate the situation."
Coming under fire-control radar is generally understood to mean that hostilities are about to commence, military experts said.
Defense Ministry officials said the use of fire-control radar on the Maritime Self-Defense Force destroyer lasted for several minutes.
"It's as if you were being held at gunpoint," said one senior ministry official. "The frontline officers must have felt pretty apprehensive."
Fire-control radar is used to lock onto a target by estimating elevation, range and velocity, before opening fire.
Warships and aircraft, including those of Japan's SDF, typically carry the equipment to determine if an "enemy" ship or aircraft is using the system, and avoid coming under attack.
Defense Ministry officials in Tokyo said a Chinese navy frigate directed fire-control radar at MSDF destroyer Yudachi around 10 a.m. on Jan. 30, from a distance of about 3 kilometers, an unusually short range between two vessels.
They said a Chinese navy frigate is also thought to have locked onto a helicopter, which had taken off from the MSDF destroyer Onami on Jan. 19. The helicopter was flying at a distance of several kilometers around 5 p.m. on the day in question. The case remains under study because of the helicopter's weak detection level.
A government source said fire-control radar was directed at Yudachi in open waters some 100-200 kilometers northwest of the Senkaku Islands, a group of five uninhabited islets and reefs that are administered by Japan, but claimed by China, which calls them Diaoyu.
The incident on Jan. 19 also occurred close to the islands.
The government source also noted that the Chinese military had targeted SDF vessels or aircraft around the Senkaku Islands with fire-control radar on several occasions in the past, including at least one instance prior to Japan's decision to put three of the islands under state ownership in September.
Switching on fire-control radar on MSDF destroyers is left to the captain's discretion because doing so signals intent to open fire.
A senior ministry official said although protocols for radar use may not be the same in the Chinese navy, it was hard to believe the two incidents represented a break in protocol of Chinese frontline officers.
Chinese navy helicopters have approached MSDF destroyers at close proximity in the past, but the latest incidents represent a ratcheting up of tensions.
"(The Chinese navy) likely provoked Japan, knowing that there is nothing Japan can do," said Koichi Furusho, a 66-year-old former MSDF chief of staff, referring to regulations that authorize the SDF to fight back only when it comes under attack.