{| |} The Fokker S.IX was a military trainer aircraft produced in the Netherlands in the mid-1930s, designed at a Royal Netherlands Navy request for a machine to replace the obsolete Fokker S.IIIs then in service. It was a conventional, single-bay biplane with staggered wings of unequal span braced with N-struts. The pilot and instructor sat in tandem, open cockpits and the undercarriage was of fixed, tailskid type with divided main units. The wing had a wooden structure, the fuselage one of welded steel tube, and the entire aircraft was fabric-covered.