Doctrine for Joint Nuclear Operations

The Doctrine for Joint Nuclear Operations was a U.S. Department of Defense document publicly discovered in 2005 on the circumstances under which commanders of U.S. forces could request the use of nuclear weapons. The document was a draft being revised to be consistent with the Bush doctrine of preemptive attack.
Doctrine.
The doctrine cites eight reasons under which field commanders can ask for permission to use thermonuclear weapons:
Overview.
Below are some quotes from the executive summary of the document.
Note: After public exposure, the Pentagon has hidden the Doctrine for Joint Nuclear Operations and three related documents, referring to this as "cancelling" the documents.
The decision to "cancel" the documents simply removes controversial documents from the public domain and from the Pentagon's internal reading list. The White House and Pentagon guidance that directs the use of nuclear weapons remains unchanged by the cancellation.
"The use of nuclear weapons represents a significant escalation from conventional warfare and may be provoked by some action, event, or threat. However, like any military action, the decision to use nuclear weapons is driven by the political objective sought."...
"Integrating conventional and nuclear attacks will ensure the most efficient use of force and provide US leaders with a broader range of strike options to address immediate contingencies… This integration will ensure optimal targeting, minimal collateral damage, and reduce the probability of escalation." ...
"Although the United States may not know with confidence what threats a state, combinations of states, or nonstate actors pose to US interests, it is possible to anticipate the capabilities an adversary might use…
These capabilities require maintaining a diverse mix of conventional forces capable of high-intensity, sustained, and coordinated actions across the range of military operations; employed in concert with survivable and secure nuclear forces" ...
"The immediate and prolonged effects of nuclear weapons including blast (overpressure, dynamic pressure, ground shock, and cratering), thermal radiation (fire and other material effects), and nuclear radiation (initial, residual, fallout, blackout, and electromagnetic pulse), impose physical and psychological challenges for combat forces and noncombatant populations alike. These effects also pose significant survivability requirements on military equipment, supporting civilian infrastructure resources, and host-nation/coalition assets. US forces must prepare to survive and perhaps operate in a nuclear/radiological environment."
In 2010 U.S. President Barack Obama, in a Nuclear Posture Review, announced a new policy that is much stricter about when the U.S. would order a nuclear strike.