U. S. Strategic Nuclear Forces: Background, Developments, and Issues
http://www.fas.org/sgp/crs/nuke/RL33640.pdf
Describes the current state of the strategic triad, land and submarine-based nuclear missiles and heavy bombers, all of which are considered delivery vehicles for nuclear missiles. Also discusses issues for Congress in deciding how large a force to maintain. From the Congressional Research Service, posted by the Federation of American Scientists.
