In the early thirties both Praga and Škoda (main competitors for both Czechoslovak army contracts but also with regard to export) designed some successful light tanks (LT-35, later the LT-38) but both companies produced some unsuccessful infantry support tank designs, notably the Praga P-IIb and Škoda Š-IIb. Subsequently, both companies worked together to design a joint infantry tank project, designated ŠP-IIb. Both companies however also continued to work on their own private attempts to build IIb/IIc category prototypes. These private attempts would later become the Praga V-8-H and Škoda T-21.