 In addition, US fire support and medical evacuation helicopters were positioned at An Thoi Naval Base on Phú Quốc island, from where they were in a better position to support the forces operating in the south.The operation began on 13 January 1971 as the 4th Armor Brigade with the 12th and 16th Armored Cavalry Regiments, three Ranger battalions, an artillery battalion, and an engineer group moved 300 kilometers from Cần Thơ to Hà Tiên in 14 hours.For the next two days the brigade pushed north along Route 4.