As the tide in the New Guinea campaign began to turn in favour of the Allies, the Japanese, having reached the zenith of their advance in New Guinea, were forced to withdraw back towards Buna and Gona. Fierce fighting subsequently followed as Australian and US troops fought to reduce the Japanese beachhead. After taking part in defeating the Japanese at Milne Bay, the 18th Brigade was transferred to Buna. The 2/9th arrived at Oro Bay aboard HMAS "Broome" on 14 December. It was the first battalion of the brigade committed to this battle. Leading the attack of 18 December, with support of M3 Stuart tanks from the &lt;a href="2/6th%20Armoured%20Regiment%20%28Australia%29"&gt;2/6th Armoured Regiment&lt;/a&gt;, it made significant gains. The 18th Brigade (and the 2/9th) continued to fight, attached to the US 32nd Division until the fall of Buna at the start of January 1943. It was returned to command of the Australian 7th Division in time to participate in an attack on 12 January against Japanese positions on the Sanananda Track that had been holding up the Australian advance there. The battalion continued fighting in the Sanananda area until it concluded with an Allied victory on 22 January. By this time its strength had fallen from over 600 to just under 100 men due to the effects of tropical diseases and heavy fighting; combat losses were recorded as 95 killed in action or died of wounds, 32 missing, and 247 wounded. These losses were offset by the arrival of 300 reinforcements during the battle, but nevertheless losses were so heavy, particularly from disease, that in February the 2/9th Battalion was transported back to Port Moresby, before returning to Australia the next month.