His major influence is mentoring Brunei's former ruler, Sultan Omar Ali Saifuddien III.

[2] In 1929 Turnbull joined the British Colonial Service as a cadet and was first attached to the District Office at Tampin in Malaya.

From 1950 to 1953 Turnbull was based in Cape Town while serving as the Chief Secretary and Deputy High Commissioner for Basutoland, Bechuanaland and Swaziland (BBS).

In his final position he was based in Jesselton as the penultimate Governor of North Borneo from 4 March 1954 until 1959.

[3] It was during this time that he appointed Keith Wookey as Resident in 1956 to Sandakan, North Borneo.