battalion and was promoted to lieutenant colonel on 9 May 1914. First World War Gallipoli When the First World War broke out, Cannan was appointed to command the Lytton Fixed Defences, holding this post from 5 to 31 August 1914. He joined the Australian Imperial Force (AIF) on 23 September 1914 with the rank of lieutenant colonel, and assumed command of the 15th Battalion. His older brother, Captain D. H. Cannan, was also one of the original officers of this battalion, the Queensland and Tasmanian battalion in Colonel John Monash's 4th Infantry Brigade. They embarked for the Middle East from Melbourne on the transport HMAT Ceramic on 22 December 1914. The ship passed through the Suez Canal safely, arriving at Alexandria on 31 January 1915, although a Turkish force was operating in the nearby desert. The 4th Infantry Brigade encamped at Heliopolis, where it resumed its training. The 15th Infantry Battalion arrived at Anzac Cove on the evening of Anzac Day, 25 April 1915. Cannan was sent with half of his battalion to fill the gap between the 2nd and 3rd Infantry Brigades. Moving in the dark through the thick scrub of the Razorback, the 15th found in the scrub the empty positions that it was sent to fill. The 15th Infantry Battalion was soon switched to Quinn's Post, one of the most exposed parts of the Anzac perimeter, with Cannan becoming post commander. In the Battle of Sari Bair on 8 August 1915, the 15th Infantry Battalion suffered heavily, having seven officers killed—including Cannan's older brother, Major D. H. Cannan—and most of the rest wounded. Cannan became ill and was evacuated from Anzac on 4 October 1915, and transferred to hospitals on Lemnos and Malta, before being sent to the 3rd London General Hospital in England. For "distinguished service in the field during operations in the Dardanelles", Cannan was mentioned in despatches and made a Companion of the Order of the Bath on 5 November 1915. Western Front Cannan resumed command of the 15th Battalion in Egypt on 21 January 1916. It departed Alexandria for Marseilles on 1 June 1916, to join the British Expeditionary Force on the Western Front. Cannan led his battalion into action again at the Battle of Pozières and Battle of Mouquet Farm. On the night of 8 August 1916, the 15th Infantry Battalion launched an attack on the German trench in front of Mouquet