In February 1942, along with the majority of the 2nd AIF, the 2/9th was withdrawn to Australia in response to the threat posed by Japan's entry into the war following the attacks on Pearl Harbor and in Malaya.
Returning via Bombay and Colombo, the 2/9th arrived in Australia, landing in Port Adelaide, South Australia, in March 1942 and from there proceeded to camp in Sandy Creek, near Gawler.
The battalion remained there until April when it was moved to Tenterfield, New South Wales, and then Kilcoy, Queensland, where it carried out training prior to departure overseas.
At this time, the strategic situation in the Pacific was finely balanced.
In July, the Japanese had landed on the northern New Guinea coast and had begun advancing along the Kokoda Track towards Port Moresby, amidst heavy fighting.
On 6 August 1942, the order to deploy came and the battalion embarked from Brisbane along with the rest of the 18th Brigade, bound for Milne Bay in New Guinea where the 2/9th arrived on 21 August to help reinforce the garrison there, due concerns about a possible Japanese landing there to secure the adjacent airfields.

From the beginning of August the Japanese had been bombing the troops of the 7th Brigade which had initially been sent to garrison the Milne Bay area, and as a Japanese invasion force was expected, the three battalions of the 18th Brigade were quickly placed into positions where they could be most effective.
The 2/9th was assigned the task of defending Milne Force Headquarters at Hagita House and the Number 1 Strip (also known as Gurney Field).
Upon arrival, the 2/9th Battalion was used to construct roads and lay steel matting on the airstrip as well as unloading stores from ships as they arrived, and carrying out patrolling operations.
Following the Japanese landing on 25 August, the battalion was placed on alert and increased its patrolling operations around the airfield; however, for five days no contact was made.
On 3 September, the battalion moved from Gili Gili to KB Mission and alongside the 2/12th Battalion, which had launched a counteroffensive along the north coast of the bay, went into battle with the Japanese for the first time.
Over the course of the next two days the Japanese were beaten back and eventually a withdrawal was ordered by the Japanese commanders.
This represented the first full-scale defeat of the Japanese on land during the war; it came at a cost for the 2/9th, though, with the battalion losing 29 men killed and a further 86 wounded in action, seven of whom later died of wounds.
Disease took a far greater toll, with a further 308 men being hospitalised due to illness.

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 2/6th Armoured Regiment, 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,
In February 1942, along with the majority of the 2nd AIF, the 2/9th was withdrawn to Australia in response to the threat posed by Japan's entry into the war following the attacks on Pearl Harbor and in Malaya. Returning via Bombay and Colombo, the 2/9th arrived in Australia, landing in Port Adelaide, South Australia, in March 1942 and from there proceeded to camp in Sandy Creek, near Gawler. The battalion remained there until April when it was moved to Tenterfield, New South Wales, and then Kilcoy, Queensland, where it carried out training prior to departure overseas. At this time, the strategic situation in the Pacific was finely balanced. In July, the Japanese had landed on the northern New Guinea coast and had begun advancing along the Kokoda Track towards Port Moresby, amidst heavy fighting. On 6 August 1942, the order to deploy came and the battalion embarked from Brisbane along with the rest of the 18th Brigade, bound for Milne Bay in New Guinea where the 2/9th arrived on 21 August to help reinforce the garrison there, due concerns about a possible Japanese landing there to secure the adjacent airfields.
From the beginning of August the Japanese had been bombing the troops of the 7th Brigade which had initially been sent to garrison the Milne Bay area, and as a Japanese invasion force was expected, the three battalions of the 18th Brigade were quickly placed into positions where they could be most effective. The 2/9th was assigned the task of defending Milne Force Headquarters at Hagita House and the Number 1 Strip (also known as Gurney Field). Upon arrival, the 2/9th Battalion was used to construct roads and lay steel matting on the airstrip as well as unloading stores from ships as they arrived, and carrying out patrolling operations. Following the Japanese landing on 25 August, the battalion was placed on alert and increased its patrolling operations around the airfield; however, for five days no contact was made. On 3 September, the battalion moved from Gili Gili to KB Mission and alongside the 2/12th Battalion, which had launched a counteroffensive along the north coast of the bay, went into battle with the Japanese for the first time. Over the course of the next two days the Japanese were beaten back and eventually a withdrawal was ordered by the Japanese commanders. This represented the first full-scale defeat of the Japanese on land during the war; it came at a cost for the 2/9th, though, with the battalion losing 29 men killed and a further 86 wounded in action, seven of whom later died of wounds. Disease took a far greater toll, with a further 308 men being hospitalised due to illness.
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 2/6th Armoured Regiment, 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,
2/9th Battalion (Australia)