According to former U.S. Ambassador to NATO and former Deputy Sec. of Defense Robert Ellsworth, from :
When asked, however, what he thought it might be, the former ambassador said it could possibly have been a missile test timed as a demonstration of American military might as President Obama tours Asia.
"It could be a test-firing of an intercontinental ballistic missile from a submarine … to demonstrate, mainly to Asia, that we can do that," speculated Ellsworth.
Ellsworth said such tests were carried out in the Atlantic to demonstrate America's power to the Soviets, when there was a Soviet Union, but he doesn't believe an ICBM has previously been tested by the U.S. over the Pacific.Here is the news video of the above speculation: