The Polikarpov I-16 is a Soviet single-engine single-seat fighter aircraft of revolutionary design; it was the world's first low-wing cantilever monoplane fighter with retractable landing gear to attain 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 Soviet Air Force at the beginning of World War II. The diminutive fighter, nicknamed "Ishak" or "Ishachok" by Soviet pilots, figured prominently in the Second Sino-Japanese War, the Battle of Khalkhin Gol, Winter War and the Spanish Civil War – where it was called the Rata ("rat") by the Nationalists or Mosca ("fly") by the Republicans. The Finns called the aircraft Siipiorava "(flying squirrel)".

Fighter aircraft are military aircraft designed primarily for air-to-air combat. In military conflict, the role of fighter aircraft is to establish air superiority of the battlespace. Domination of the airspace above a battlefield permits bombers and attack aircraft to engage in tactical and strategic bombing of enemy targets.