Graduating from the two-year course in December 1929, Ritchie served with his regiment until being sent to India and made a GSO2 with Northern Command, India, a post he held from 2 April 1933 until 1 April 1937. While there he was promoted, for the first time in almost sixteen years, to brevet major on 1 July 1933, major on 2 June 1934, and brevet lieutenant colonel on 1 January 1936. On 4 December 1936 Ritchie married Catherine Taylor, daughter of James A. Minnes, from Kingston, Ontario, Canada. They had two children; Arnott Dugald Neil and Isobel Anne. On 3 January 1938 Ritchie transferred from the Black Watch, which by now he had been with for just over twenty-three years, to the King's Own Royal Regiment (Lancaster), and was promoted to lieutenant colonel. He became Commanding Officer of the 2nd Battalion, King's Own on the same date and took command of the battalion in Palestine, then engaged in internal security duties during the Arab revolt. Aided throughout this difficult period by his adjutant, Captain Richard Anderson, he commanded the battalion until August 1939, shortly before the Second World War began in September. For his services in Palestine Ritchie was mentioned in despatches. After handing over the battalion to Lieutenant Colonel John Hardy, Ritchie returned to England, where he was promoted to colonel on 26 August 1939 (with seniority backdated to 1 January) and was made a GSO1 at the Senior Officers' School at Sheerness, Kent.