It's important to note that Security Force Assistance occurs under a variety of conditions, and it is the conditions that will determine how and with what organizations we use to accomplish the mission.
We have military cooperation agreements with more than 125 nations around the world and often provide security force assistance in response to host nation requests. This assistance is generally delivered by Offices of Security Cooperation, always under the control of the US Embassy Country Team, and is accomplished by a mixture of assigned military and civilian personnel, contractors, and mobile training teams. These mobile training teams come from either the General Purpose Forces --- perhaps more appropriately described as Multi-Purpose Forces --- or from the Special Forces depending on the type of training requested.
Under conditions of active conflict where we have direct responsibility for security -- as in Iraq and Afghanistan -- tactical commanders will have a security force assistance mission to train, advise, and assist tactical host nation forces. This mission is accomplished using the resources of the modular brigade augmented as necessary based, again, on conditions. The conditions include the state" of security -- described in doctrine as Initial Stage, Transforming Stage, and Sustaining Phase -- as well as the capacity and capability of the host nation security forces. Security Force Assistance at the Institutional Level will be accomplished by a Security Transition Headquarters organized under the Joint Task Force. This Security Transition Headquarters partners with the US Embassy Country Team and evolves over time into an Office of Security Cooperation as described above.
Finally, we have security relationships with some nations facing significant internal security challenges but which, for many reasons, may not accept a large, visible US military presence within their borders. If they request Security Force Assistance under these conditions, the mission is generally assigned to US Special Operations Forces, potentially augmented by regionally-oriented General-Purpose Forces.
Clearly, the future operational environment will require us to demonstrate as much versatility in Stability Operations as we have in Offense and Defense Operations. Understanding the variety of conditions under which Security Force Assistance occurs is an important first step.