NOTE: according to the Attestation Form, O'Brien embarked with the 10th Light Horse Regiment, 31st Reinforcements, on board HMAT A73 'Commonwealth'. However, on p. 22 of his service file (Form B103), it states he embarked from Fremantle on board HMAT 'Canberra', 24 November 1917.
Marched in to Reinforcements Camp, Moascar, 21 December 1917.
Marched out to Australian Provost Corps, 15 April 1918.
Admitted to No 2 Australian Stationary Hospital, 24 July 1918 (malaria); diagnosis changed to bronchitis, 28 July 1918; discharged to Desert Mounted Corps Rest Camp, Port Said, 9 August 1918.
Marched in to 3rd Light Horse Training Regiment, Moascar, from Rest Camp, 21 August 1918.
Transferred to 10th Light Horse Regiment, 29 August 1918.
On leave, Egypt, 5 Febriary 1919; reported absent, 15 February 1919.
Found guilty, 26 February 1919, of when on Active Service being absent from 0800, 15 February, until apprehended by the Military Police at 0800, 25 February 1919: awarded 14 days' Field Punishment No 2, and forfeited a total of 24 days' pay.
Admitted to Field Punishment Compound, Abbassia, 27 February 1919; discharged (conduct good), 11 March 1919.
Rejoined 10th Light Horse Regiment, 12 March 1919.
Wounded and remained at duty, Zagazig, 19 March 1919.
Commenced return to Australia on board HT 'Oxfordshire', 10 July 1919; disembarked Fremantle, 4 August 1919; discharged (termination of period of enlistment), Perth, 27 August 1919. AWMM