[7] In early 1919, Harcourt was attending a staff course in the United Kingdom when he heard about the deteriorating situation in North Russia.

[12][13] These men formed part of the North Russia Relief Force (NRRF),[13] which departed for Archangel in the SS Czar and Czarina.

[4][15] The unit carried out patrols and probing raids in their area of operations and Harcourt was tasked with planning an attack on Bolshevik positions around Emtsa.

Harcourt's force was tasked with capturing an artillery battery in the main Bolshevik position, however, his guide led him to the wrong objective in the darkness and suddenly the company came under intense and unexpectedly heavy fire.

[17]The engagement ended with the surrender of the Bolshevik forces, however, as Harcourt prepared his men for an advance south to Vologda he received orders to pull back to Archangel and eventually they were evacuated back to England where the men were demobilised and Harcourt returned to the Royal Dublin Fusiliers.

[4] The significance of this find was not immediately realised until 1942 when, after the Japanese invaded Burma and subsequently gained control of the only known route out of Burma, British intelligence recalled Harcourt's discovery and using this information the Allies were able to route their withdrawing armies and the large numbers of refugees around the main Japanese force back into India.

[4][19] On 28 April 1939, while he was working with the Youth Employment Office in Hobart, Harcourt was involved in a motor vehicle accident at Kings Meadows, Launceston.

[21] When the Second World War broke out in September 1939 Harcourt sought to return to the United Kingdom to rejoin the British Army.

As his job was considered vital to the war effort, the Australian government prevented him from leaving, however, he was eventually allowed to join the Militia.

[5] In mid-1942, Harcourt was seconded for special duties and was temporarily posted to the Guerrilla Warfare School[23] that had been set up at Wilsons Promontory in Victoria to begin training independent companies in irregular warfare techniques based on the recommendations of the British Military Mission in Australia, headed by Lieutenant Colonel J.C.

[27][28] On 6 August 1942, the 2/6th Independent Company disembarked in Port Moresby and shortly afterwards it was placed directly under the command of the headquarters of the 7th Division.

[29] As the Japanese began to advance over the Owen Stanley Range towards Port Moresby the company began patrolling operations to the west of Port Moresby and Harcourt was given responsibility for advising divisional headquarters of Japanese movements around the Kokoda Track and to provide protection for the division's flanks.

[30] Later, in November and December 1942 the company fought alongside the 126th and 128th Infantry Regiments around Buna, where they were used mainly in the reconnaissance role, but also as assault troops where necessary.

[32][33] At the end of the fighting around Buna Harcourt was decorated with the Silver Star for gallantry[28][34] by General MacArthur, who later singled the 2/6th Independent Company out for special praise in his Order of the Day on 9 January 1943.

[36] In writing the official history of the Australian involvement in the early campaigns in the Pacific, Dudley McCarthy described Harcourt as being "an intrepid officer whose forty-seven years seemingly had done nothing to lessen his zest for living, his energy or his physical endurance".

[39] During this time, Harcourt was also actively involved in Legacy, helping to establish facilities at Coningham, teaching night classes in carpentry and metal work.

In 1955, he was appointed an Officer of the Order of the British Empire in the Queen's Birthday Honours List for his community work and involvement in the public service.