Berney-Ficklin was gazetted into the 1st Battalion, Norfolk Regiment in June 1914, shortly before the outbreak of the First World War. Promoted to the temporary rank of lieutenant on 22 September 1914, he transferred to the 8th (Service) Battalion, Norfolk Regiment, a Kitchener's Army unit in which his brother was also serving, which formed part of the 53rd Brigade of the 18th (Eastern) Division, as the battalion's adjutant. Promoted to the temporary rank of captain on 11 January 1915 and lieutenant on 26 February, his battalion departed for the Western Front in July. He was awarded the Military Cross (MC) on 5 June 1916 and was promoted to temporary major on 1 July, the first day of the Somme offensive in which his division played a significant role, notably on 1 July. The following year he became brigade major of the 152nd (Seaforth Highlanders) Brigade, part of the 51st (Highland) Division, a Territorial Force (TF) formation. On 9 July 1917, the same year of his fathers' death, he married Audrey Brenda Knyvet Wilson at St Peter Mancroft, Norwich. In March 1918, during the German Army's Spring Offensive, Berney-Ficklin was wounded and taken prisoner.