The explosion of the Maine in Cuba on February 15, 1898 was ruled by a Naval Court of Inquiry in March of 1898 as caused by a mine explosion. Subsequantly many different views of what caused the explosion have been put forward to a fire in her coal bunkers to a fire in her powder magazines. In 1976 a group of American Naval Investigators concluded that a fire ignited the Maines magazines.
The answer to the question however remains that experts cannot definitively say what the cause of the explosion was.