The S.33 was one of the most successful early French commercial aircraft and was developed throughout the 1920s, culminating with the S.126. It was first operated on regular Paris-London services in 1921 by GMA.
The S.33 - originally powered by a 186.3kW Salmson Z.9 engine but later fitted with a 194kW CM.9 - accommodated a pilot and four-five passengers (four passenger seats in the cabin). Altogether 40 aircraft were built, serving with several European airlines. From the S.33 was developed the S.46 powered by a 279.5kW Lorraine-Dietrich 12Da engine, 38 of which were produced. The S.56 was essentially similar to the S.33 but was originally powered by a 279.5kW Gnome Rhone-built Jupiter engine, had larger-span wings with duralumin spars and wooden ribs, and different cabin windows. The prototype - with a single elongated window on the starboard side of the fuselage and a similar window and two round windows (one on each side) on the port side - set up a height record in 1923 of 8,200m while carrying a 250kg useful load. About 20 S.56 were built, the major version of which was the Type 56/4 with a roomy cabin for six passengers in the centre-section of the fuselage and the open pilot's cockpit in front of the cabin instead of behind. The cabin was well ventilated, heated and amply provided with opening windows. The S.66 designation applied to earlier aircraft incorporating some refinements. The S.116 and S.126 were one-offs with 335.3kW Renault or Hispano-Suiza engines respectively.