After taking part in the fighting in Syria and Lebanon, the battalion undertook garrison duties around Tripoli before being transferred back to Australia in 1942.

[12] In January 1941, with the threat of invasion of England reduced, it was decided to send the 2nd AIF units there to the Middle East and the battalion arrived in Egypt in March 1941.

[4] Following this the battalion moved to Palestine where it undertook further training and received a draft of reinforcements which enabled it to raise a fourth company in order to bring it up to establishment.

Coming under fire from Vichy French troops on the hills overlooking the town, the battalion suffered a number of casualties, including its commanding officer, Lieutenant Colonel Selwyn Porter.

During the fighting that followed, one of the battalion's members, Private James Gordon, performed the deeds for which he subsequently received the Victoria Cross, crawling forward and single-handedly attacking a French post that was holding up his company's advance.

[4] Following this, the battalion established itself at Amchite where they undertook occupation duties until mid-September when the 25th Brigade received orders to move to Tripoli.

[24] From June they began jungle training in preparation for deployment to New Guinea in September where the units of the Militia had been fighting a delaying campaign against the Japanese along the Kokoda Track.

[25] On 31 August, under the command of Lieutenant Colonel Colin Dunbar, the battalion was moved to Brisbane where they embarked upon the Cremer bound for Port Moresby.

In December, however, Miller died from scrub typhus,[29] and as the casualties from combat and disease mounted the battalion was eventually withdrawn from the fighting to Port Moresby from where it embarked to return to Australia in January 1943.

[4] After this the battalion spent over a year training on the Atherton Tablelands in Queensland[33] before moving to Morotai and then later taking part in the landing at Balikpapan along with the rest of the 7th Division in one of the last Australian campaigns of the war.

[4][34] Landing at Green Beach on 2 July 1945, the second day of the operation, the 2/31st went ashore unopposed and moved inland, taking up positions in the centre of the Australian line around a location called "Ration".

[35] After establishing themselves on the hill, later in the day they were struck by airburst artillery before commencing clearing patrols and occupying a smaller feature known as "Resort".

Relying heavily upon direct and indirect fire support to suppress the Japanese positions along the numerous ridges that lay astride the axis of advance, the going was slow.

By 9 July the open country of the coast turned to thick bush and the Australians began to encounter improvised explosive devices and booby traps in the scrub.

[38] Early on 10 July, a company from the 2/31st Battalion launched a successful attack which saw them capture 12 3-inch naval guns that were being used as part of the Japanese defensive system for the loss of five wounded.

[4][41] During the fighting around Balikpapan the 2/31st Battalion suffered the highest number of casualties of any Allied unit deployed in the Borneo campaign,[4][42] losing 44 men killed and 134 wounded.