HONG KONG • Increased interactions between the Chinese and US navies in the contested South China Sea risk becoming more complicated by the increasingly sophisticated missiles carried by Chinese submarines, including one which can accelerate to as much as three times the speed of sound before hitting a target, making it harder for a crew to defend their ship.

A new report to the US Congress notes that the YJ-18 missile can cruise at just under the speed of sound, only a few metres above the surface of the sea and then, about 20 nautical miles from its target, accelerate to as much as three times the speed of sound.

"The supersonic speed makes it harder to hit with on-board guns," according to Mr Larry Wortzel, a member of the US-China Economic and Security Review Commission. "It also makes it a faster target for radars."

The YJ-18's speed and long range, as well as its wide deployment "could have serious implications for the ability of US Navy surface ships to operate freely in the Western Pacific" in the event of a conflict, the commission found.

The report came just days after US warship USS Lassen entered the 12-mile zone around the reefs in the disputed Spratly Islands chain that Beijing had turned into man-made islands.

BLOOMBERG