When the Australian government committed 3 RAR, Army Headquarters determined that it would be led by an officer who had served in World War II and had a distinguished record. The commanding officer, Lieutenant Colonel F. S. Walsh, who had been in command of the battalion for a year, was to be replaced. Still attending Staff College, Green was chosen. He left Australia for Japan on 8 September, and took over command of 3 RAR on 12 September. He oversaw another two weeks of unit training in Japan, then flew to South Korea on 25 September to await the battalion's arrival. 3 RAR arrived in Pusan on 28 September. By that time, the KPA was retreating back into North Korea following the Inchon landings and Pusan Perimeter Offensive. Green's battalion joined Brigadier Basil Coad's 27th British Commonwealth Brigade, part of the force under the Commander-in-Chief United Nations Command, General of the Army Douglas MacArthur. On 5 October, the entire brigade was airlifted by the United States Air Force (USAF) from Taegu to Kimpo Air Base outside Seoul, their vehicles driving the intervening and only arriving in Seoul on 9 October. The brigade then moved north under the operational control of the US 1st Cavalry Division.