China, Finland, Spain, and the Soviet Union used the Polikarpov I-16.
The debut of the I-16 was at the May Day parade in Moscow in 1935.
Spanish Civil War
278 I-16s were used by the Spanish Republican forces. The I-16/6 was the first model to be used in combat in November 1936. Hispano-Suiza also license built I-16s.
Was known as Mukha (fly) in Spain.
In 1939 the I-16 fought against the Japanese on the Manchurian border.
Soviet ace, Grigori Ravchenko shot down three Japanese aircraft in China and led an I-16 unit in Mongolia.
Finland used captured I-16s.
Invasion of Soviet Union
When the Germans invaded in June 1941 the I-16 was the most numerous fighter in the Soviet arsenal. Approximately 2/3 of the fighter force were I-16s.
Some I-16s remained in service until the summer of 1943 when it was finally withdrawn due to its obsolesence.