into action 4 November, when I-15s shot down two Junkers Ju 52/3ms and two CR.32s over Madrid, and forced a third Ju 52 and a Heinkel two-seater to crash-land. No losses were reported among the Soviet pilots. During the next two days, Chato pilots claimed 12 more victories, at the cost of two I-15s lost. On 16 November, while dogfighting with Fiat CR.32s over Madrid, future ace Rychagov was shot down and four days later the number of combat-ready Polikarpov in the central area had fallen to 15 aircraft: seven had been lost in combat, two had force-landed and one was undergoing repair. In December 1936 and January 1937, two more shipments of 30 aircraft arrived in Spain, making it possible to form four full-strength I-15 squadrons. Until the spring of 1937, central Spain was the main war theatre for I-15s. And in May 1937, another batch of 31 Polikarpov landed in Spain, taking the total number of I-15s delivered to 116. Chato losses in the Spanish Civil War were comparable to those of its principal rival, the Fiat CR.32. By 1 January 1939, 197 Polikarpovs had been lost: 88 shot down by enemy aircraft and nine by anti-aircraft artillery, 27 destroyed on the ground and 67 written off in accidents. World War II More than 1,000 I-15bis fighters were still in Soviet use during the German invasion when the biplane was employed in the ground attack role. By late 1942, all examples still in service had been relegated to second line duties. Variants TsKB-3bis Prototype. TsKB-3ter Prototype fitted with the more powerful M-25V radial piston engine. I-15 First production series. I-15bis Single-seat fighter biplane, armed with four PV-1 or ShKAS machine guns, plus up to of bombs. The I-15bis was powered by the more powerful Shvetsov M-25V radial piston engine. It had a straight upper wing. A total of 2,408 machines were built. I-152 Modernised version of I-15bis. One built in 1938. Series production was not undertaken, since it was decided to build I-153 instead. I-152GK (Germetichyeskoi Kabine – hermetic (pressure) cabin) – One aircraft fitted with a pressure cabin. I-152TK (Turbo Kompressor – turbo-charged) – One aircraft fitted with two turbochargers. I-15ter (I-153) Development of the I-15 with retractable landing gear, see Polikarpov I-153. UTI-1 (Oochebno Trenirovochnyy Istrebitel' – fighter trainer) – Factory-built two-seat trainer version, front cockpit moved forwards, dual controls fitted, 20 built in 1934 but