Sudan. (Ethiopia). 1944. Air Mail envelope written from 'Sudan Interior Mission, Private Mail bag to Kurmuk, Postmaster Khartoum, Anglo-Egyptian Sudan' addressed to Illinois bearing Sudan SG 46, 10p violet and grey tied by Sudan Air Mail/ Khartoum date stamp '24th Mar 44' with 'P.C. 90/ Opened by Examiner/ MM/ 4243' label, endorsed 'Air Mail'.
After the Italians declared war on 10th June 1940, hostilities began on the Sudan - Ethiopia - Eritrea border. The Italians occupied Kurmuk on the 7th July 1940 and the Post Office was closed. Nice usage of the Private Mail Bag scheme.