South-Atlantic Airmail Flown by Air France and Deutsche Lufthansa
During the 1930s, two European airlines competed and then cooperated to offer twice-weekly transatlantic airmail service between Europe and South America. Deutsche Lufthansa took the lead in early 1934 by establishing dependable bi-weekly, all-air service which eventually became weekly service. The French effort to achieve such consistency took longer, but by early 1936, Air France was advertising weekly service. The two airlines adopted very different approaches to bridging the Atlantic, with the result that collectors of the mail flown by Air France tend to emphasize flights by famous pilots such as Jean Mermoz. That material is detailed in the illustrated catalog Ligne Mermoz: Histoire aérophilatélique, Latécoère, Aéropostale, Air France, 1918-1940 edited by Gérard Collot and Alain Cornu. Deutsche Lufthansa developed a system of catapulting the mail in a flying boat that was carried out to sea for a day to limit the fuel load necessary for the flight. Those mail flights are catalogued by James W. Graue and John Duggan in the volume Deutsche Lufthansa: South Atlantic Airmail Service, 1934-1939.
A recent addition to the web that illustrates some of the mail transported on these routes can be found at this link: https://transatlanticmailbyair.wordpress.com