The force, numbering about 55 men and under the command of the then Major Edward Puttick, was based on Fiji for two months before returning home. Promoted to captain the following year, he spent two years in Dunedin instructing the Territorial Force artillery, before being posted to Auckland. There, he was in charge of harbour defences. In 1925, he was sent to a gunnery course in England and, for the following two years, was seconded to the Royal Artillery. He returned to New Zealand in 1927, accompanied by his wife Barbara Waiohine Howe, who he had married in Birmingham on 30 August the previous year. A series of staff and instructional postings in Wellington, and then Auckland, followed. He was promoted to major in 1932. In 1937, Parkinson was made commander of the Royal New Zealand Artillery, having been made a temporary lieutenant colonel. He was demoted to major the following year; this reduction in rank was as a result of disciplinary action after using the workshop facilities at Trentham Military Camp for personal work. In 1939, he was returned to his temporary rank of lieutenant colonel. A lot of his work as commander of the artillery involved the implementing programs for the upskilling of gunners and non-commissioned officers to perform leadership roles normally the preserve of officers. Likewise, officers were expected to learn basic gunnery tasks. Following the outbreak of the Second World War, Parkinson's rank was made substantive and was later seconded to the Second New Zealand Expeditionary Force (2NZEF). He was given command of the 4th Field Artillery Regiment and embarked with the First Echelon of the 2NZEF in early 1940. After serving in the initial stages of the Western Desert Campaign, for which he was mentioned in despatches, he led the regiment well during the Battle of Greece. He was later awarded the Distinguished Service Order (DSO), gazetted on 14 April 1942, due in part to his service during the battle. In late 1941, Parkinson, newly promoted to brigadier, returned to New Zealand to take over the recently formed 1st New Zealand Army Tank Brigade. After Japan's entry into the war, he became commander of the 7th Infantry Brigade, the army reserve in New Zealand, for several months before reverting to his previous command. The tank brigade was eventually disbanded when the 4th Infantry Brigade, based in Egypt, was converted to armour. Parkinson returned to the Middle East and took over command of the 6th Infantry Brigade.