sentences:  Eventually a "tumblehome" design of around 16,000 tons with two long-range guns and 128 missile tubes was selected as the DD-21, the Destroyer for the 21st century.The program ended in November 2001, with a version of the DD-21 emerging as the DD(X) or "Zumwalt" class destroyer.It was envisaged that the DD-21 hull would be used for a future air defense cruiser (CG-21), which then eventually evolved into the CG(X) program.