Captain Mills (Wellington College, Berkshire, Royal Military Academy Sandhurst) was wounded in World War I at La Bassée and wrote a pair of books, his first, about that experience: With My Regiment: From the Aisne to La Bassée (J. B. Lippincott & Co.: Philadelphia, 1916) and Hospital Days (T. Fisher Unwin: London, 1916) under the pseudonym Platoon Commander.
He received his first Military Cross as an “immediate award for courage and leadership” at La Bassée where, as commander of the battalion's anti-tank platoon, equipped only with three Hotchkiss guns Ordnance QF 2 pounders, they knocked out 21 German tanks from Rommel's 7th Panzer Division, while protecting the retreat of the allies to the beaches during the Battle of Dunkirk.
On 3 August 1915 between Cambrin and La Bassée, France, a German trench-mortar bomb landed on the side of the parapet of the communication trench in which Second Lieutenant Boyd-Rochfort was standing close to a small working party of his battalion.
Lady Dorothy married Captain Arthur F. H. Mills of the Duke of Cornwall's Light Infantry after he was wounded in the First World War in 1916, being presented at the ceremony with a wedding ring made from a bullet that had been surgically removed from his ankle after he was wounded in combat at La Bassée, France.
He was killed in action on 2 October 1915, while leading the 6th Welsh in a night attack on the Hohenzollern Redoubt, near La Bassée, aged 32.
World War I: La Bassée 1914, Festubert 1914 '15, Givenchy 1914, Neuve Chapelle, Aubers, Loos, France and Flanders 1914–15, Megiddo, Sharon, Damascus, Palestine 1918, Aden, Kut al Amara 1915 '17, Ctesiphon, Defence of Kut al Amara, Tigris 1916, Baghdad, Khan Baghdadi, Sharqat, Mesopotamia 1915–18, Persia 1918, North West Frontier India 1915 '16–17, Baluchistan 1918;
After the death of his father he inherited Revel Counties and de Broglie, the marquisate of Senonches and also received the Government of La Bassee, near Lille.