麦克马洪线
When he was deputy foreign secretary, Caroe is credited with getting the Government of India to reaffirm the McMahon Line, which had been negotiated by a former Foreign Secretary Henry McMahon with Tibet in the Simla Convention of 1914. 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. For various reasons, the Simla Convention was not operationalised until 1935, and the official publication of the treaties of the Government of India, "Aitchison's Treaties", did not include it. Caroe obtained the British government's permission to revise the official Indian maps to show the McMahon Line as the new boundary and to include the Simla Convention in a revised volume of "Aitchison's Treaties" but to do so "unobtrusively". Caroe reissued the new volume in 1938, but still carrying the original 1929 date, and had the original volumes withdrawn. When the matter was discovered in 1963, it gave rise to accusation of a "virtual falsification" of the official records. Scholar Karunakar Gupta states that Caroe's zeal in operationalising the McMahon Line warrants it being renamed the "McMahon–Caroe Line".