The baseline US force in Iraq has been roughly 15 combat maneuver brigades for the past three years, and before that it was roughly 17 combat maneuver brigades in 2004 and 2005. The baseline force has been slowly decreasing because the Army is out of rested units, and has been burning through its operational, strategic and training reserves as exemplified by the lack of a ready brigade of the 82nd Airborne Division for long stretches of time, the deployment of the 11th Armored Cav. Regiment which is normally a training unit and the extension of combat deployments to fifteen months with a goal of a year to reset between extended tours.
However as I recently wrote that fifteen brigades is a '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.' So why is fifteen brigades now barely sustainable when it was an incredible strain in 2003 or 2005?
A couple of things have changed. The most basic change has been in units of account. A 2008 brigade is organized significantly differently than a typical 2003 or 2005 brigade. This has allowed for a 33% increase in combat brigade with minimal real increases in active duty Army end strength or combat battalions.
In 2003, there was no such thing as a 'uniform' brigade organization. Most combat maneuver brigades had three combat battalions, a small recon/scout unit, a headquarters unit, some type of artillery attachment and then smaller attachments of specialists. But this was not a hard and fast rule. For instance some divisions had three brigades but ten heavy combat battalions. So one brigade would be assigned four battalions. An armored brigade from the 3rd Infantry Division looked different than an armored brigade from the 1st Armored Division. And then you had odd ball brigades such as the two active duty Armored Calvary Regiments which had three and a half large battalions and an odd helicopter attachment and the 173rd Airborne Brigade had two small infantry battalions. But if you took as a rule of thumb that a US brigade in 2003 had three battalions on average, the US Army had thirty three combat brigades and roughly 100 combat maneuver battalions. Fifteen brigades in combat meant roughly 45 battalions were in combat.
Now the Army is at the tail end of a brigade reorganization and expansion from thirty three combat brigades to forty two brigades (soon to expand to forty eight brigades). These brigades are standardized into two basic shapes. The first is the modular brigade combat team with two battalions of combat maneuver units, a very large recon and scout unit, smaller artillery units and more support soldiers. This is the plan for the vast majority of Army brigades. Now a heavy brigade based in Germany will be the same as one in Georgia and that will be the same as one in Texas. The other type of unit will be the Sryker Intermediate brigades which will be triangular in structure with three combat battalions and relevant support units. The Army will have forty two combat brigades and roughly 100 combat maneuver battalions. Now fifteen brigades in combat means roughly 30 to 35 battalions are in combat depending on the number of un-modular brigades and Stryker brigades are deployed.
The number of headquarters deployed are the same, but the total combat maneuver strength deployed is significantly less than it was in 2003-2005 when a typical US brigade was significantly larger than the new modular brigades.