In January 1915, as the British were moving troops from India into Mesopotamia through the Persian Gulf and Basra, Wilson was designated as the assistant, and then deputy, to Sir Percy Cox, the British Political Officer for the region. Based in Baghdad, he then became the acting Civil Commissioner for Mesopotamia. The problem remained that there was no official "Arab Policy"; it had not been defined in law nor by the Civil Service. India wanted Mesopotamia as a Province; but Arabists from Cox downwards wished for a semi-autonomous policy separate from the Arab Bureau in Cairo. Policy was made "ad hoc"; but Wilson disagreed.