"Successes achieved by I-15 biplanes during the Spanish Civil War and against the Japanese Navy Mitsubishi A5M monoplanes in China, prompted further development of the design into the I-15bis, with uprated 750hp M-25V engine, four machine guns, and provision for two 165lb bombs; and the I-153 with M-62 or M-63 engine, provision for six rockets or two bombs, and a retractable undercarriage which helped to increase maximum speed to 267mph. Both types served in the campaigns against Finland, and were still operational in large numbers at the time of the German invasion, in June 1941.
The I-15bis was used mainly in the dive-bomber role by that time. The I-153, which weighed only 4,431lb fully loaded, was so maneuverable that it fared reasonably well against even the much faster Bf 109s of the Luftwaffe."
