Because the Russian word for "100" ("сотка" — "sotka") sounds somewhat like the pronunciation of "STO", the STO was later renamed KB-100, and there Petlyakov proposed the development of a twin-engine interceptor against high-altitude long-range bombers, particularly those being developed in Germany such as the Junkers Ju 86P and Henschel Hs 130. His proposal was accepted in March 1938, with the requirement that the first prototype be ready for its first flight before the end of 1939. The project was initially given the name Samolyot 100 (lit. "Aircraft 100") and later called VI-100 ("Vysotnyi Istrebitel" — "High-Altitude Fighter").