Polikarpov I-16 image - Aircraft Lovers Group

The Polikarpov I-16 was a Soviet fighter aircraft of revolutionary design; it was the world's first cantilever-winged monoplane fighter with retractable landing gear. The I-16 was introduced in the mid-1930s and formed the backbone of the Soviet Air Force at the beginning of World War II. The diminutive fighter, nicknamed "Ishak" ("donkey") by Soviet pilots, prominently featured in the Second Sino-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").
It also was one of the longest-lived fighters of the period, serving until as late as 1950, in Spain.