[GuerraCivil]

I took a look on what Mikhail Maslov has to say about the family of I-15 fighters. The most controversial is "I-152" which actually was not the same as I-15 bis, although it is widely used in English/American literature. The I-152 was a modified version of I-15 bis and it did not go to mass production. The I-152 was a kind of I-15 bis with retractable landing gears (but not with seagull upper wing), if I have understood Maslov right. The I-153 was a "I-15, third version" and thus become I-153 when it went to mass production.

Some of the technical solutions remain unclear for me. If the seagull wing was considered so bad reducing visibility in I-15 ("I-151"?), why did Polikarpov return to it in I-153 and why pilots accepted it in the new plane? As far as I know, the Spanish Republican pilots had no problem with seagull wing.