Iran: First test of Global Nuclear Strike Capability?
If the US were to strike Iran, what would the nature of the strike be? One likely component would be low yield mini-nukes or “bunker busters”. I thought it would be informative to look at some of the military planning and preparations for such a strike. Obviously planning for a strike can just be one of many contingency plans. On the other hand, the details of such planning reveals what the range of options the administration is considering. The further along the preparations the more likely it’s a realistic option.
On January 10, 2003, the new Unified Command Plan (Change 2) assigned a new mission to STRATCOM: Global Strike. The Unified Command Plan defined the new mission as: "providing integrated global strike planning and command and control support to deliver rapid, extended range, precision kinetic (nuclear and conventional) and non-kinetic (elements of space and information operations) effects in support of theater and national objectives."
The military operationalization of the Global Strike mission is Contingency Plan (CONPLAN 8022), which became operational in the fall of 2004. (1)
The Space and Global Strike command is responsible for implementing and executing nuclear preemptive strikes under CONPLAN 8022 (Global Strike), if ordered to do so by the President.
In the summer of 2004,Rumsfeld approved a top secret "Interim Global Strike Alert Order" directing the military to assume and maintain readiness to attack hostile countries that are developing weapons of mass destruction, specifically Iran and North Korea 
as Arkin notes:
It is difficult to imagine a U.S. president ordering a nuclear attack on Iran or North Korea under any circumstance. Yet as global strike contingency planning has moved forward, so has the nuclear option
As U.S. military forces have gotten bogged down in Afghanistan and Iraq, the attractiveness of global strike planning has increased in the minds of many in the military. Stratcom planners, recognizing that U.S. ground forces are already overcommitted, say that global strike must be able to be implemented "without resort to large numbers of general purpose forces."
Ok so we know that the capability of a global strike is operational, but its operation should be covered by the appropiate doctrine. From the Doctrine for Joint Theater Nuclear Operations, February 1996
"The dissolution of the Soviet Union has greatly reduced the possibility of a large scale nuclear exchange. However, the loss of the stability inherent in a clearly bipolar world has increased the likelihood of a nuclear exchange by regional powers. In addition, the threat to the United States, its allies, and its deployed forces due to the proliferation of
WMD has grown following the end of the Cold War. The flow of advanced technology to potential or actual hostile nations has led to a proliferation of systems (missiles and aircraft) capable of delivering WMD. The possibility of a WMD exchange in a regional conflict has risen dramatically, threatening our forward-deployed forces and challenging our long-range power projection capabilities."
Specifically what targets can be considered for a tactical strike:
WMD and their delivery systems, as well as associated command and control, production, and logistical support units. Ground combat units and their associated command and control and support units. Air defense facilities and support installations. Naval installations, combat vessels, and associated support facilities and command and control capabilities. Nonstate actors (facilities and operation centers) that possess WMD. Underground facilities.
Note the inclusion of nonstate actors!
Lets look at the most recent policy document: Doctrine for Joint Nuclear Operations,2005
The new doctrine incorporates preemption into joint nuclear doctrine for the first time, lowers the threshold for nuclear use further by reducing the level of hostilities where U.S. nuclear weapons might be used, endorses a role of nuclear weapons against all forms of weapons of mass destruction, endorses a role of nuclear weapons against terrorists, and describes missile defenses as a means of defending nuclear forces rather than people against attack.
From the same source
The new doctrine’s approach grants regional nuclear strike planning an increasingly expeditionary aura that threatens to make nuclear weapons just another tool in the toolbox. The most extreme example of this is nuclear preemption, which the revised doctrine enshrines into official U.S. joint nuclear doctrine for the first time by describing at least four scenarios where geographic combatant commanders might request Presidential approval for use of nuclear weapons first.
In nuclear preemption, the objective no longer is deterrence through threatened retaliation but battlefield destruction of targets with nuclear weapons first in anticipation that deterrence will fail. The use of nuclear weapons might occur at a much lower intensity level than envisioned during the Cold War, and the new doctrine replaces "war" with "conflict" to describe the lower intensity of hostilities that could involve the use of U.S. nuclear weapons in post-Cold War nuclear battlefields.
Well exactly what kinds of nukes might they use and what would be the effects of using them? Well to diffuse some criticism, the adminstration has talked about using a "few small" bombs that could penetrate the earth, hit the underground targets and have minimal effect on the environment. But according to CONPLAN8082 they would use somewhere between 5-10 bombs.
According to the plan, each bomb would have a 10-kiloton yield - about two-thirds of that of the bombs dropped on Hiroshima and Nagasaki.
Each detonation of a bomb a few meters underground would destroy most of the buildings on the surface to a range of two kilometers. After the explosion, there would be a need to quickly evacuate civilians from an area of 100 square kilometers, to avoid the deadly effects of the radioactive fallout; buildings, agricultural crops and livestock would be affected in an area of thousands of square kilometers, and depending on wind direction and velocity, there could be a need to evacuate more people from thousands of additional square kilometers.
The nuclear policy that the Bush administration continues to formulate, including plans for a preemptive nuclear strike against states that do not possess such weapons and the development of new nuclear weapons - is a recipe for disaster. It is a policy that blurs the line between conventional and nuclear war. This blurring could undermine the relative strategic stability that has set in since the Cold War.
From the Armscontrolwonk the effects of detonating a bunker buster a few meters under ground:
1. The explosion cannot possibly be contained underground, and deadly radiation would spread hundreds of miles downwind.
2. Tens of thousands to a million or more people would likely be killed if this weapon is used.
3. Despite its enormous yield, it is ineffective against bunkers that are deeper than 300 meters underground, a distance reached easily by current tunnelling technology.
4. In attacks against underground stocks of chemical or biological weapons, the explosion is more likely to release the deadly agents above ground than it is to destroy them.
In another article the Armscontrolwonk goes into great detail about what a strike against Iran might look like. Its extremely detailed and informative si I recommend that you go over and read it. I'll just relay the conclusions drawn from some war game scenarios that have been run [from the same Armscontrolwonk article].
Newsweek reports that participants have not been pleased with the outcome of airstrikes in IC sponsored wargames. An Air Force source told Newsweek that “The war games were unsuccessful at preventing the conflict from escalating.”
This is essentially the same outcome in the Atlantic Monthly game. Writing in the New Republic, my friend Mike Mazarr (who played SECDEF) expressed some very serious concerns about escalation:Iranian leaders would have very real reasons to respond to “surgical” strikes with an all-out assault on U.S. interests designed to provoke the sort of decisive clash that everyone assumes Iran wants to avoid. And the resulting conflict would have far worse consequences for the United States than Iran’s ability to create weapons-grade nuclear material.