Earlier this week Cernig asked about the impact of President Bush's punting plans to keep at least fifteen combat brigades in Iraq. The short story is that assuming nothing else in the world blows up, this is a (barely) sustainable force level especially if one projects that 2009 will be a repeast of OIF-3 as the year of the National Guard in Iraq.
Right now the active duty Army has forty two modular combat brigades, and the Marines have another eight infantry regiments. The Army will also be adding another six brigades over the next three years to the active duty roster. The projected requirements for these fifty brigades are one permanent brigade in South Korea, two brigades in Afghanistan (although recently reinforced by a weak brigade equivilant of Marines) and then fifteen brigades in Iraq plus whatever contigencies elsewhere, including the Sinaii, the former Yugoslavia and anything else.
If you remove the one South Korea based brigade from consideration, forty nine active duty brigades are needed to cover at least seventeen brigade deployment slots. That is slightly less than three brigades per slot. That is not the ideal two years to rest, refit and reset per year in combat, but it is better than the fifteen months in combat and twelve months to reset which is the current pace. Once you consider transportation and acclimation time, and assuming a twelve month tour of duty, the typical brigade will have roughly eighteen to twenty months at the home station exclusive of transit/acclimation between combat deployments.
If anything this analysis is a bit limited as it is excluding National Guard formations from consideration. We know seven National Guard combat brigades are being alerted for Fall 08 and Winter 09 deployments and four National Guard brigades have either recently deployed to Iraq or are currently in transit/acclimation to Iraq. This is a significant amount of breathing room built into the rotation schedule.