Japan planned to sail a maritime defense ship in 2016 into an area claimed by China as its territorial waters in the South China Sea, in response to a similar move by China in Japanese waters to the north, sources familiar with Sino-Japanese ties said Saturday.
The planned move, a Japanese equivalent of the "freedom of navigation operation" conducted by the U.S. Navy in the South China Sea, was never carried out, however, over concerns that going ahead with it would seriously harm bilateral ties, according to the diplomatic sources.
The Chinese government led by President Xi Jinping has in recent years aggressively pressed its territorial claims in regional waters, including over the Japanese-administered Senkaku Islands in the East China Sea.
Chinese coast guard patrol ships have routinely sailed near the uninhabited islands, sometimes entering territorial waters around them. China calls the islands Diaoyu.
On June 9, 2016, a Chinese naval ship entered a band of waters just outside the 12-nautical-mile territorial waters around the Senkakus for the first time. It also sailed toward the territorial waters.
Six days later, another Chinese naval ship entered the territorial waters near Kuchinoerabu Island, some 70 kilometers from the southern tip of the main island of Kyushu in the country's southwest.
The Japanese government took the set of Chinese actions as signaling a higher level of intensity that warranted a new response, according to a senior defense force officer.
Officials at the government's National Security Secretariat subsequently began considering possible countermeasures, including in response to the Chinese coast guard ships that had entered the waters around the Senkakus.
One countermeasure devised mainly by the Maritime Staff Office within the Defense Ministry involved sailing a Maritime Self-Defense Force ship through the area China considers its territorial waters around an artificially made island in the South China Sea.
Such a freedom of navigation operation was to be conducted en route to and from the sea off Somalia where the Japanese maritime force has conducted anti-piracy escort missions, and there was no plan to announce it afterward to avoid provoking Beijing to the extreme.
Even without announcing the operation, it was deemed possible to send a message to China because the Chinese side would surely detect the close passage by a Japanese naval ship, according to the sources.
But the plan was never implemented as the government under then Prime Minister Shinzo Abe was at the time making diplomatic moves that were aimed at improving Sino-Japanese ties with a view to realizing a first visit by Xi to Japan.
"China would try to use any unguarded moment to its advantage," one of the sources said in explaining the plan. "It is therefore indispensable to consider various responses."
China claims most of the South China Sea and, to buttress its claims, has built artificial islands there with military fortifications. But the U.N. Convention on the Law of the Sea does not recognize territorial waters for artificial islands.
The convention at the same time stipulates that "ships of all States, whether coastal or land-locked, enjoy the right of innocent passage through the territorial sea."
The United States, arguing that the waters around the Chinese-made artificial islands are international waters, has repeatedly sent naval vessels through them. It has asserted "navigational rights and freedoms," consistent with international law.