The sinking of the R.M.S. Lusitania by a German submarine in 1915 helped lead the United States into World War I, but more than a century later, researchers are still trying to determine what exactly happened to the doomed British luxury liner.

For years, divers have searched for clues amid the twisted wreck, which lies on the ocean floor roughly seven miles off the southern coast of Ireland. Each discovery holds the potential for answers. Their most recent find: the ship’s main telegraph, a sturdy metal contraption whose retrieval was announced last week by the Irish government.

But researchers said the discovery would do little to answer questions that have clouded the story of the ship’s destruction: Why did the Lusitania sink so quickly — in just 18 minutes, compared with the two hours and 40 minutes it took the Titanic to go down? Was it carrying a secret cargo of munitions for the British war effort, and if so, did that help doom its passengers?

These questions stem from an unexplained second explosion that occurred deep inside the ship shortly after it was struck by a torpedo on May 7, 1915. That second explosion is still being investigated, but speculation has long focused on whether it was caused by munitions on board, a charge German officials made at the time, said Diana Preston, a British author and historian.