As a direct result of concern over the escalating cost of fighter manufacture, the French government and air force instituted a program for chasseurs légers or 'light fighters' in 1926. This was unofficially known as the 'Jockey' program, and it envisaged the use of moderate guns, minimal equipment and small amounts of ammunition. Emphasis was placed on climb rate, endurance and a ceiling (high for the time) of 8000 metres. To meet this requirement, Morane-Saulnier designed the MoS-121, renamed the MS 121 in 1927. The prototype appeared in that year and was a single-seat parasol monoplane of mixed construction.