Near collision between US and Chinese warships raises questions

According to United States defence officials, "on 5 December, while lawfully operating in international waters in the South China Sea, USS Cowpens and a PLA Navy vessel had an encounter that required manoeuvring to avoid a collision".

The incident occurred while the Cowpens was conducting surveillance on sea trials of China's new - and one and only - aircraft carrier, the Liaoning. This incident has been called the "worst" since the 2009 Impeccable incident, in which several Chinese surveillance vessels "harassed" the US sub hunter in China's exclusive economic zone. But such encounters between the US and Chinese navies are becoming rather frequent.

According to the limited public information available, the Chinese captain of the ship involved and possibly the commander of the fleet accompanying the Liaoning had apparently violated the International Maritime Organisation's 1972 Convention on the International Regulations for Preventing Collisions at Sea - ratified by both China and the US. The Chinese commanders may also have tried to constrain the Cowpens' "freedom of navigation".

But there are extenuating circumstances that neither the US nor China has revealed. Perhaps these extenuating circumstances are the reason both sides have agreed that "no one violated international law".

Apparently China had set up an "inner defence layer" or "no sail" zone around the exercises, and its "maritime authorities" had posted a "navigation notice" to this effect on their website. It now seems that the run-in began after a Chinese navy vessel sent a hailing warning and ordered the Cowpens to stop or leave the area, which of these is not clear. The Cowpens refused the order because it was operating in international waters.

Then a Chinese tank landing ship sailed in front of the Cowpens and stopped, forcing the Cowpens to abruptly change course to avoid a collision.