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. 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 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.
Western Front (right) at Quinn's Post, Anzac with Brigadier General
Harry Chauvel (left). Cannan is the officer in his shirt sleeves.|alt=Six men in uniform with peaked caps satand and sit in a circle talking to each other. In the background are sandbags, tins and clothing hung out to dry. Cannan resumed command of the 15th Battalion in Egypt on 21 January 1916. It departed
Alexandria for
Marseille on 1 June 1916, to join the
British Expeditionary Force on the
Western Front. On the night of 8 August 1916, the 15th Infantry Battalion launched an attack on the German trench in front of Mouquet Farm known as Park Lane. Cannan's men captured their objectives, and indeed went beyond them in some places. However, the
Suffolk Regiment on his flank was mown down by German machine gun fire and Cannan was compelled to withdraw part of his force to a more defensible position. On 30 August 1916, Cannan was appointed to command the
11th Infantry Brigade by Major General John Monash, now commander of the
3rd Division. At this time the 3rd Division—of which the 11th Infantry Brigade was part—was training on the
Salisbury Plain in England. Cannan returned to France with the 11th Infantry Brigade in November 1916, His citation read: In the fighting in 1918, the 11th Infantry Brigade was the first to check the German advance towards
Amiens, repelling a German attack at
Morlancourt in late March. In July, it was selected from the brigades of the 3rd Division to participate in the
Battle of Hamel. The 11th Brigade went on to participate in the
Battle of Amiens and the
Hundred Days Offensive. His citation read: For his services on the Western Front, Cannan was also awarded the
Belgian Croix de Guerre, his citation noting his "tenacity, thoroughness and efficient organisation", "his splendid qualities of leadership", and his "personal gallantry." He was mentioned in despatches another five times. ==Between the wars==