Complex sentence: The Tradewind Task Force came under the overall command of the United States Sixth Army; its main combat elements were the XI Corps headquarters, the 31st Infantry Division and the 126th Regimental Combat Team (RCT) from the 32nd Infantry Division.
Split into simpler sentences: The Tradewind Task Force came under the overall command of the U.S. Sixth Army. The Task Force's its main combat units were the 31st Infantry Division and the 126th Regimental Combat Team (RCT) of the 32nd Infantry Division.