Commissioned into the Royal Artillery in 1914, he finished the First World War as a highly decorated soldier. He then served with Gen. Edmund Ironside with British forces in the Russian Civil War. In 1920-1921, he had duty in Ireland, in a counterinsurgency role. 
Beginnings of WWII
In 1938, he joined the War Office guerrilla warfare research unit, first called GS(R) and them MI(R), with Major J.C.F. ("Joe") Holland and Peter Fleming. While he visited the German borders and Yugoslavia, his primary activity was writing "how-to" manuals for guerrillas.
Just before the start of WWII in Europe, in August 1939, he was sent, as a major, with a British assistance and observer mission to Poland, as chief of staff of the British Military Mission, with the secret assignment of assisting the Poles and Czechs with the organization of anti-Nazi guerrilla forces. A week after the German invasion, he escaped to Romania, and then, using false documents, returned home. He led special operations units to the Norwegian campaign, which ended before his raiders, which would have moved on fishing trawlers, could enter the action.
Special Operations Executive
- Patrick Howarth (1980), Undercover, the men and women of the Special Operations Executive, Routledge, pp. 4-8
- Stephen Budiansky (2008), Churchill's secret army: Britain's last resort against a Nazi invasion was a guerrilla force trained to carry out suicidal missions of terror and sabotage, The Free Library
- New Document Releases: Special Operations Executive Records Release, United Kingdom National Archives, 8 February 2002