With Messerschmitt concentrating on the design and build of combat aircraft the design of a larger transport/airliner based on the design of the large Messerschmitt Me 323 military transport was sub-contracted to Zeppelin. The aircraft was to be built in France by SNCASO.
The ZSO 523 would be like the Me 323 a high-wing monoplane but was larger with both a front and rear loading ramp. Powered by six 1618 kW (2200 hp) Gnome-Rhône 18R engines it also had a six-wheel retractable main landing gear. Calculations show that with a load of 22 tons the ZSO.523 can reach a distance of 2,200 km, while the maximum load was 46 tonnes.