With over 40,000 units built, the Polikarpov Po-2 (known initially as the U-2) has the distinction of being the most widely produced aircraft in history. Nicknamed Kukuruznik (Corn Cutter), it was designed originally as a light biplane trainer but ended up serving in a wide variety of roles and became one of the most disliked aircraft by the Germans on the Eastern Front. Pre-war versions served in transport, air ambulance and agricultural duties but the outbreak of war prompted its use or conversions for other roles including liaison, air observation, and as a propaganda aircraft with a loudspeaker. Neverthless, it was most recognizable as a night harrassment aircraft for nuisance raids usually operating close to the front lines, some even flown by female pilots nicknamed the 'Night Witches'. They were difficult to shoot down on account of their speed being inferior to the stall speed of Bf 109 and Fw 190 fighters. Although the bulk of production was undertaken during the war, manufacturing continued afterward, mostly in Poland after 1948 and was additionally used by a large number of Soviet client states.

The prototype U-2PK was first flown in 1927 but had poor performance which was corrected in the redesigned U-2 whose maiden flight took place on 7 January 1928. Around 13,000 had been built by the outbreak of war including the U-2VS military version which led to a number of wartime variants such as the U-2LSh light attacker, the U-2S air ambulance, U-2P seaplane, U-2GN propaganda aircraft, U-2NAK air observation post, and U-2ShS staff liasion. Night harassment models were designated as the U-2LNB while a basic trainer was known as the U-2UT. Lastly, transport versions included the U-2SP and the U-2SPL with an enclosed rear cabin. After the death of Nikolai Polikarpov in 1944, the aircraft was redesignated Po-2 although Polish-built variants were known as the basic CSS-13 utility aircraft and the CSS-S-13 air ambulance.