A senior US admiral is being sent to Tokyo with a presidential letter and an apology for the sinking of a Japanese trawler that has left nine people lost at sea.
Admiral William J Fallon has been named Special Envoy to Japan and will arrive in Tokyo with a letter from President Bush to Prime Minister Yoshiro Mori.
Mr Mori has called it extremely deplorable that civilians were at two control stations aboard the USS Greeneville when the submarine hit the fishing boat.
Mr Fallon will explain the progress of the ongoing investigation, the US Navy has said in a statement.
The admiral will discuss prospects for salvaging the Japanese vessel, which was accidentally rammed on February 9 and sank in 2,000ft of water off Honolulu.
The boat was on a trip to teach Japanese high school students commercial fishing, and four of the missing are students.
US officials say reports of serious crew errors aboard the Greeneville right before the collision raised the possibility that the Navy's formal investigation could spread beyond three officers already named as subjects of the inquiry.
It may also include a sailor whose job was to plot positions of nearby vessels and possibly other people.