 Complete the following phrase:  The regiment remained on Ceylon until July 1942, when the 16th and 17th Brigades completed their return to Australia. Arriving in August, the regiment was reconstituted at Greta, New South Wales. By this time, in New Guinea, the Japanese were advancing towards Port Moresby. The Militia troops that had initially delayed the advance had been reinforced by the 21st and 25th Brigade, and together these troops halted the Japanese advance. The 16th Brigade was subsequently deployed as the Australians began a counter offensive to push the Japanese back to their beachheads around BunaGona. The 21st Field Regiment was assigned to the defence of Port Moresby initially, but in November detached elements of the 51st Battery to support the US 32nd Infantry Divisions attack on Buna, while the remainder of the battery was assigned to support the 7th Divisions attack on Gona. In January 1943, the 2nd Battery, and regimental headquarters, moved forward to Buna, and the 1st Battery was moved to Wau where they supported Kanga Force during the 