On 1 August 1915, Mackinolty transferred to the Australian Imperial Force, to lead a team of thirteen other mechanics as reinforcements for an Australian Flying Corps contingent serving in the Mesopotamian campaign. He departed Melbourne nine days later aboard RMS "Persia", and arrived at Basra on 1 September. Mackinolty's team immediately joined No. 30 Squadron Royal Flying Corps (originally the Mesopotamian Half Flight AFC), which moved into the city of Kut after its capture by British Empire troops in the Battle of Es Sinn. The unit took part in the Battle of Ctesiphon in November, and organised supply drops to the British and Indian garrison in Kut during the siege that lasted from December 1915 until the following April.