Upon the return of the division headquarters and 1st Brigade, the 10th Mountain Division began the process of transformation into a modular division. On 16 September 2004, the division headquarters finished its transformation. The 1st Brigade became the 1st Brigade Combat Team, while the 3rd Brigade Combat Team, 10th Mountain Division was activated for the first time. In January 2005, the 4th Brigade Combat Team, 10th Mountain Division was activated at Fort Polk, Louisiana. 2nd Brigade Combat Team would not be transformed until September 2005, pending a deployment to Iraq.