Polikarpov I-16

The  Polikarpov I-16 was a Soviet fighter aircraft of revolutionary design; it was the world's first low-wing cantilever monoplane fighter with retractable landing gear to have attained operational status and as such "introduced a new vogue in fighter design." The I-16 was introduced in the mid-1930s and formed the backbone of the SovietAir Force at the beginning of WorldWar II. The diminutive fighter, nicknamed "Ishak" ("donkey") by Soviet pilots, prominently featured in the SecondSino-Japanese War, the Battle of Khalkhin Gol and the Spanish Civil War — where it was called the Rata ("rat") by the Nationalists or Mosca ("fly") by the Republicans. The Finnish nickname for I-16 was Siipiorava ("Flying Squirrel").

Polikarpov I-16 in The War That Came Early
The I-16 was the major front line fighter available to the Soviet Air Force when war broke out in 1938. Although a revolutionary design, it was outdated by newer fighters like the 109. In spite of it's obsolescence, it was kept in the front line because it was all the Russians had.

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