He went overseas in 1914 as a Major in the 30th Battalion. Then in May 1915 Peck joined as a
lieutenant colonel in the
16th (Canadian Scottish) Battalion,
Canadian Expeditionary Force. He was 44 years old. He became the commanding officer of the Regiment during the
Battle of the Somme (1916). Peck was awarded the
Distinguished Service Order (DSO) in the 1917
King's Birthday Honours; a
Bar to the DSO, for which the citation in the
London Gazette read, "During an attack he showed fine courage and leadership. He led his battalion, under difficulties caused by heavy mist, to its final objective, nearly three miles, after severe fighting. He personally led his men in an attack on nests of machine guns protecting the enemy's guns, which he captured. Some of the guns were of 8-inch calibre."; was
Mentioned in Despatches five times; and was wounded twice. On 2 September 1918 at
Cagnicourt,
France (the Drocourt-Queant Line), when Lieutenant Colonel Peck's command, after capturing the first objective, was held up by enemy machine-gun fire, he went forward and made a personal reconnaissance under very heavy fire. Returning, he reorganized his battalion and pushed them forward. He then went out, under the most intense artillery and machine-gun fire and intercepted the tanks, giving them the necessary directions, pointing out where they were to make for, and thus paving the way for an infantry battalion to push forward. To this battalion he subsequently gave the necessary support. The full citation was published in a supplement to the
London Gazette of 12 November 1918 (dated 15 November 1918): ==Later life==