Following WWII, special treaty rates continued to be applied to mail to the Belgian Congo. They were discontinued when Belgian Congo gained independence on July 1, 1960, after which the general UPU rates applied to mail to the former Belgian Congo. The post-WWII rates provide a special challenge for the collector of modern-era postal history--a field that is yet to be fully exploited.
This five-gram airmail cover posted in 1945 from Luxembourg-Ville to Leopoldville-Kalina illustrates the six-franc, five-gram airmail surcharge (April 6, 1945 to January 4, 1947) and the three-franc, 20-gram letter rate (October 1, 1945 to January 1, 1946), with postage paid by a five-franc 1944 Charlotte definitive and the 1.50 and 2.50 franc 1945 Lion definitives.
The four-gram airmail cover shown here illustrates the three-franc, five-gram airmail surcharge (July 1, 1953 to July 1, 1960) and the three-franc, 20-gram letter rate (January 1, 1949 to July 15, 1958), with postage paid by the 6 franc 1946 airmail [Prifix 12]. The cover was posted at the Luxembourg Telegraph Office, April 7, 1955, to Nya-Lukemba, Kivu, Belgian Congo. Backstamps document its arrived at Bukavu, capital of South Kiva, on April 11th and Nya-Lukemba the next day.