View source for DDG - Guided Missile Destroyer

A guided missile destroyer is a destroyer designed to launch guided missiles. Many are also equipped to carry out anti-submarine, anti-air, and anti-surface operations. The NATO standard designation for these vessels is DDG. Nations vary in their use of destroyer D designation their hull pennant numbering, either prefixing, or dropping it altogether. The U.S. Navy has adopted the classification DDG in the US hull classification symbol.

http://en.wikipedia.org/wiki/Guided_missile_destroyer