strettell fought in world war i. he was based in england when the war began and so raised the service squadron of the 6th dragoons, which he commanded as a temporary major between october 1914 and june 1915 and was made a full major on the first day of september 1915. the following february, he was posted to mesopotamia; he served as a brigade major in the 7th indian cavalry brigade between december 1917 and april 1919, a deputy assistant quarter master general in india between june and november 1919, and a general staff officer in india between december 1919 and september 1920. strettell was then appointed brigade major in the egyptian expeditionary force, but relinquished his post in december 1921. having been a brevet lieutenant-colonel since 3 june 1919, he was appointed to the full rank on 25 april 1924 and a colonel on 1 november of that year (with seniority to the previous june).