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.