Crunchy, on 07 July 2012 - 08:55 PM, said:
2nd Australian Division. Not an infantry unit, but one of the other arms or service units. Depends on colours on the patch.
This unit patch would indicate the 2nd Machine Gun Battalion which was the MG detachment incorporated as part of the 2nd Division, AIF.
The crossed arms below the patch signify an MG unit. The four companies in each division were consolidated into MG battalions in March 1918.
If the photo was taken prior to that date it could be any of the MG companies (5th, 6th, 7th or 22nd) that later comprised the 2nd MG Battalion.