 He was commissioned into the City of London Yeomanry and during World War I he fought in Egypt, France and at the Battle of Gallipoli, ending the war as a Major.After the war, Pery continued to serve in the City of London Yeomanry, which became a Royal Artillery brigade, and inherited his half-brother's titles in 1929.Lord Limerick was an Honorary Colonel of the City of London Yeomanry (TA) from 1932–52, Vice-Chairman from 1937–41 and then Chairman of the City of London Territorial and Auxiliary Forces Association from 1941–50 and Vice-Chairman from 1942–49, then Chairman from 1949–54, then President of the Council of Territorial and Auxiliary Forces Associations from 1954–56.