when contemporary aircraft in the US and Germany were of all-metal construction with retractable undercarriages. Some of these had better performance, but the S.73 remained competitive for some years. Operational history The first operator of the S.73 was the Belgian airline SABENA, which purchased five Gnome-Rhône 9Kfr Mistral Major-powered S.73s from Savoia-Marchetti in 1935, introducing them on European routes in the summer of 1935. Two of these aircraft were lost in accidents in 1935. Seven more S.73s, powered by Gnome-Rhône 14K Mistral Major engines, were built for SABENA under license by SABCA in 1936–1937, which allowed the S.73 to replace the Fokker F.VII on the service from Belgium to the Congo. This service took four days (with no overnight flying) with a flight time of 44 hours. The second operator of the S.73 was the Italian airline Ala Littoria, which received at least 21 examples, powered by a variety of engines, including the Piaggio Stella X, the Wright R-1820 and the Alfa Romeo 126 RC.10. They were used on services within Europe and to Italy's African empire. In December 1935, an S.73 was used for a journey from Italy to Asmara, delivering over 200,000 letters, with 6,600 km (4,100 mi) traveled in four days, followed by the return trip to Rome on 6 January 1936. A commercial line was established covering a 6,100 km (3,790 mi) journey. Other users included Avio Linee Italiane (powered by Alfa Romeo 126) and Československé Státní Aerolinie (powered by Walter Pegasus). At the outbreak of World War II the S.73 was already obsolete, but some of the aircraft were pressed into service with the Regia Aeronautica for operations in Abyssinia and Spain. Nine S.73s were present in Eastern Africa and used as military transports. Owing to the poor military situation, with British Commonwealth forces on the brink of capturing Addis Ababa, the Duke of Aosta, the Viceroy of Italian East Africa, ordered the remaining three S.73s to be evacuated. After several days of preparation, they took off from Addis Ababa on 3 April 1941 with 36 men on board, planning to fly to Kufra in Libya, away, requiring additional fuel tanks in the fuselage. All three aircraft force-landed in the desert, but refuelled at Jeddah, before resuming their journey. After several days of difficulties, including sand storms that clogged up the air filters, they took off again. Initially, it was planned to make another landing