The United States has lodged a protest with China over an incident Sunday in which the Pentagon says five Chinese vessels harassed an unarmed U.S. Navy research ship in international waters in the South China Sea, and engaged in potentially dangerous maneuvering.  Pentagon officials say this is the latest in a series of such incidents in recent days.

A U.S. Navy photo shows that one of the Chinese ships is fairly large and has "China Marine Surveillance" written on its side.  The other ships are smaller and also do not appear to be warships.  

Dangerous maneuvers at sea

But Pentagon Spokesman Bryan Whitman says the Chinese ships surrounded the American ship and maneuvered aggressively and dangerously.

"This was a reckless and dangerous maneuver that was unprofessional and that violates the international law [requirement] to operate with due regard for the rights and safety of other users of the ocean," Whitman said.

A news release says two of the Chinese ships stopped directly in front of the USNS Impeccable, forcing it to make an emergency stop.  The release says U.S. crew members sprayed water from a fire hose at one of the Chinese ships, and the U.S. ship radioed the Chinese asking for a safe path out of the area.

US says Impeccable is research vessel

Bryan Whitman says the Impeccable is a research vessel, which carries no significant weapons.  According to the U.S. Navy, the ship is 84 meters long and 25 meters wide, and half its 50 crew members are civilians.  Whitman says the ship was conducting routine "ocean surveillance" in international waters 120 kilometers south of China's Hainan Island when the Chinese ships approached aggressively, one to within eight meters.

"These are dangerously close maneuvers that these vessels did," Whitman noted. "They also dropped pieces of wood in the water directly in front of the Impeccable's path.  They also used poles in an attempt to snag the Impeccable's towed acoustical array."

The towed array is a piece of sonar equipment.

Some Chinese crew members undressed down to underwear

Whitman said some of the Chinese crew members undressed down to their underwear in an apparent show of disrespect, what Whitman called an "immature" display.  But he said the close maneuvering and attempts to disrupt the U.S. ship's progress were serious.

"This is not the first time that there has been some provocative maneuvering, but I think this is one of the most aggressive incidents that we have seen in some time," Whitman said.

The official release says Chinese ships and aircraft have engaged in "increasingly aggressive conduct" toward U.S. Navy ships in recent days.  It cites three previous incidents, two of them involving the same American ship, in which Chinese ships, including a navy frigate, approached at close range, shined lights and verbally harassed U.S. ships by radio.  In another incident, a Chinese aircraft flew at low altitude alongside the Impeccable 11 times.