I believe the History Channel has a pretty detailed look at all three ships (the Britannic being the third). The Britannic struck a mine in the Mediterranean Sea during WWI (ca 1916, I think), and sank in an hour. But due to lessons learned on the Titanic, only 2 dozen or so lost their lives, and all of those due to the explosion, not the sinking. The Olympic survived to eventually be sold as scrap - many of the extremely elaborate fixtures ended up in fancy hotels in Europe.

On the alleged name change, considering there were literally thousands of men working on these ships day and night for months on end, pulling a name change would have been quite the trick, eh? Just another urban legend....