 In 1917, Wrench joined the Royal Flying Corps.He reached the rank of major and served as principal private secretary to Lord Rothermere when he was President of the Air Council, and later as his deputy when controller for the dominions and United States at the Ministry of Information.As a result of his experience in this last appointment, Wrench founded in 1918 the English-Speaking Union of the Commonwealth "in no narrow attitude of race pride, in no spirit of hostility to any people" and created the mission statement of the English-Speaking Union in the first edition of the organization's magazine, "Landmark"