As Foreign Secretary, he was responsible for reviving the McMahon Line, which included the Assam Himalayan frontier (present day Arunachal Pradesh) within India.
Scholar Peter Brobst calls him the "quintessential master of the Great Game" and the "foremost strategic thinker of British India" in the years before independence.
The McMahon Line ran along the crest of the Himalayan ranges east of Bhutan, and incorporated the present day Arunachal Pradesh within the territory of India.
[10] After the war, Caroe was appointed as the Governor of the North-West Frontier Province (NWFP), on the northwest border of the Indian subcontinent, adjoining Afghanistan and Russia.
[13] His strategic ideas proved influential in the United States: At about this time there were those in Washington, looking for ways to secure the oil resources and practice containment in the middle east.