However, due to the U.S. Army's recent reorganization, only 4th Squadron remains in active service. 4th Squadron, 10th Cavalry takes its history and lineage from D Troop, 10th Cavalry. In 2000, D Troop, 10th U.S. Cavalry, was reactivated and assigned as the brigade reconnaissance troop for 3rd Brigade Combat Team, 3rd Infantry Division at Fort Benning, Georgia. D Troop, 10th Cavalry was deployed with 3/3 ID to Iraq in 2003, and was deactivated upon redeployment in 2004. It was reactivated in October 2007 at Fort Carson, Colorado, replacing the 2nd Squadron, 9th Cavalry regiment, as the 4th Squadron, 10th Cavalry Regiment with A, B, C, and HQ Troops as the reconnaissance squadron for 3rd Combat Brigade Team  of the 4th Infantry Division. The 4th Squadron deployed to Iraq with the BCT from December 2007 to February 2009, and again in March 2010. The Squadron deployed to Jordan in 2015 in support of Operation Spartan Shield. In February 2016, Delta  Tank Company from 1st Battalion, 8th Infantry Regiment moved to 4th Squadron, 10th Cavalry Regiment to be assigned as Dakota Troop. As of February 2016, 4th Squadron, 10th Cavalry Regiment is the only current active unit of the 10th Cavalry Regiment.
Question: What group replaced the 2nd Squadron at Fort Carlson, Colorado in October 2007?
Answer: D Troop, 10th Cavalry