According to the U.S.F.K. spokesman as reported by the Korea Times:
Navy Times, also not known as a Nork mouthpiece, reported the incident thusly:
A U.S. Navy group of four ships― three warships and one salvage vessel ― have joined South Korea's rescue and recovery operations for its sunken frigate, the Cheonan.
Kim Yong-kyu, spokesman for the U.S. Forces in Korea (USFK), provided information on the U.S. Navy's participation in operation.
The spokesman said its participation was made at the request of South Korean authorities.
The four U.S. ships belong to the U.S. 7th Fleet, based just south of Tokyo.
"They were participating in Key Resolve/Foal Eagle Exercise, a joint Korea-U.S. military drill which will continue until the end of April," the spokesman added.
The Japan-based cruiser Shiloh, destroyers Curtis Wilbur and Lassen and the salvage ship Salvor — carrying a team from Mobile Diving and Salvage Unit 1 — were ordered to help with the search after the South Korean government asked the U.S. for help, a Pentagon official told Navy Times.
The U.S. ships were already at sea when the South Korean patrol ship Cheonan sank on Friday as part of the international exercise Foal Eagle, the official said. The cause of the sinking is still not clear.
The "official" is a Pentagon official who was talking to Navy Times but "asked not to be identified because of the delicacy of the situation involving North and South Korea".
Maybe some reporting glitches here, but Foal Eagle was still going on with the participation of three Aegis-class destroyers. The Navy Times article does confirm that the U.S. ships were not at their base in Japan and, with the phrase "already at sea", welcomes the reader to draw the inference that the ships were not in the area when the Cheonan sunk. It will be interesting if the report on the sinking describes the location of friendlies at the time of the incident. (CH, 5/9/09)
Asia Times published an article, Pyongyang sees US role in Cheonan sinking, by Kim Myong Chol, identified as "often called an "unofficial" spokesman of Kim Jong-il and North Korea."
He asserts that North Korea had nothing to do with the March 26 sinking of the South Korean frigate Cheonan off the west coast of the Korean peninsula and on the South Korean side of the NLL (Northern Limit Line), the de facto and frequently disputed maritime border between the two antagonists.
Kim makes the interesting point that the Cheonan was engaged in an annual joint US/ROK military exercise known as Foal Eagle 2010 and several Aegis destroyers were in the area. Presumably all this high-tech military hardware would be able to detect the presence of a North Korean intruder.
He also raises the possibility of the Cheonan being done in by friendly fire.
It's reported that the Cheonan's sister ship, the Sokcho, was also in the area and marked the incident by firing wildly toward North Korean territory at a flock of birds on its radar instead of steaming to the Cheonan's rescue.
So shaky fire discipline by the Cheonan's own team during a complicated multi-vessel exercise near hostile territory looks like a potential hazard/explanation.
With this context, conspiracy theorists will have a field day with this paragraph from the Korea Times on May 7:
The multinational investigation team is also closely looking into the possibility that a North Korean submarine fired a German-made torpedo used both by South Korean and American navies in an attempt to dodge its responsibility.
The report of the team is supposed to be out around May 20.
H/T to DJ for the tip.