The Japanese entered the war in December 1941 and as they advanced south towards Papua, the 49th found itself under air attack. Throughout the Kokoda Track campaign, an attempt was made to fly elements of the battalion to Kokoda to support the 39th Battalion during the Battle of Kokoda, but this proved abortive. Later, troops from the 49th Battalion joined Honner Force, an ad hoc unit tasked with conducting long-range patrols along the Goldie River to prevent the Japanese from cutting the track, while the rest of the battalion established standing patrols between the Goldie and Laloki Rivers. Although no contact was made with the Japanese, the combat role helped improve the outlook of the soldiers and morale improved. Throughout the preceding months the battalion's strength had been increased and by September 1942 it had a strength of 37 officers and 818 other ranks, including a draft of 12 officers who had been posted from experienced Second Australian Imperial Force units in August. The battalion continued to expand throughout October and November, by which time more than half its personnel had volunteered to transfer to the AIF. Training opportunities remained limited, though, even as preparations were made to send the unit into battle. Around this time, the battalion's machine gun company was detached and in conjunction with several other Militia machine gun companies, it was used to form the 7th Machine Gun Battalion.