Dewar enlisted early, joining the New Zealand Expeditionary Force leaving on 15August 1914 for German Samoa. On his return he volunteered again, joining the 9th Wellington Mounted Rifles as a machine gunner and was based at Awapuni Racecourse, Palmerston North; he was promoted quickly to sergeant. On 16October 1914, after training, Dewar embarked on the "Orari" at Wellington en route for Egypt. There, Dewar captained the Wellington Mounted Rifles rugby team in several matches against other regiments — beating the First Australian Light Horse, the Canterbury Mounted Rifles, and the Auckland Mounted Rifles — before his regiment landed on 8August 1915 at Anzac Cove, Gallipoli. Twenty-four hours later, on 9August 1915, Dewar lost his life in the assault on Chunuk Bair — Albert Downing was killed in the same action, the first All Black to be killed in the war. Sergeant Henry Dewar is commemorated on the Chunuk Bair (NZ) Memorial Turkey (Panel 4).