The Pentagon has drafted a revised doctrine for the use of nuclear weapons that envisions commanders requesting presidential approval to use them to preempt an attack by a nation or a terrorist group using weapons of mass destruction. The draft also includes the option of using nuclear arms to destroy known enemy stockpiles of nuclear, biological or chemical weapons.

http://www.washingtonpost.com/wp-dyn/content/article/2005/09/10/AR2005091001053.html