The 3rd Light Horse Field Ambulance departed Alexandria for Gallipoli on 17 May 1915. It moved to Lemnos in June, where it operated a hospital, but returned to ANZAC Cove for the August offensive. Downes missed this operation, as he remained on Lemnos supervising the hospital until he returned to Anzac on 11 August. He remained with his unit until 13 November, when he departed for Lemnos and then Egypt.