For the first time, Japan’s defence ministry publicly declared engaging in a strategic military drill within a South China Sea.
Tokyo revealed the submarine, Kuroshio, joined three other ships in a joint exercise on anti-submarine warfare last week, in a bid to declare resistance to Chinese territorial expansion in the South China Sea.
After the naval exercise, the Kuroshio headed to a Vietnamese naval base in Cam Ranh Bay, the ministry said.
The move comes as a nod to US allies, who have hit out against Chinese military expansion in the South China Sea.
Tokyo’s initiative could infuriate Beijing, who claims territory over most of the contested waters, sending their once seemingly good relationship into tatters.
Relations between the Asian superpowers have improved over recent years, after both countries faced newly imposed US economic sanctions on their exports.
However, Chinese foreign ministry spokesman Geng Shuang called on Tokyo to “respect the efforts made by regional countries to resolve the South China Sea issue through talks”.
He added: “Act with caution and don’t take any acts that could damage peace and stability in the region.”
Noburu Yamaguchi, a retired lieutenant-general in the Ground Self-Defence Force told the Financial Times: «There is a clear improvement in Japan-China relations and the latest exercise was carried out with the understanding that it wont be too provocative.
«Japan believes it is the kind of exercise that every country has done and is entitled to carry out.»
Over the years, China has built effective missile systems and military stations on artificial islands in the South China, claiming territorial control over the region.
In August, the Royal Navy’s HMS Albion bypassed Beijing-claimed Paracel Islands, in a bid to challenge China’s «excessive claims» over the South China Sea.
In June, UK Defence Secretary Gavin Williamson announced plans to send three warship to the contested waters «to send the strongest of signals» to countries that «don’t play by the rules».
This follows US Secretary of Defence, James Mattis warning to China, declaring the country would suffer «consequences» if it continued to expand control over the region.
In May, two US warships came 12 nautical miles away from Chinese-claimed islands, with Beijing warning Washington to stop “provocative actions that violate Chinese sovereignty.”
The US has previously announced hopes for more international initiative towards challenging Chinese claimed territories in the South China Sea.