The Polikarpov design bureau (OKB) was ordered, in 1936, to begin development of a fast twin-engined aircraft that could be used for ground attack duties and as a heavy fighter. It delivered the ground attack version the following year for evaluation, although it could be modified as necessary for other roles. The VIT-1 was reasonably successful, but it was decided to give it more powerful engines and modify its structure. The improved aircraft was designated as the VIT-2.[1]
The VIT-1 was a low-winged, twin-engined aircraft with a mixed structure. The monocoque fuselage was made in halves of 'shpon', molded birch plywood. The wing and tail structures were built from a mix of steel tubes and duralumin with a duralumin skin. The VIT-1 had the first metal-skinned control surfaces in the USSR.[2] The main legs of the conventional landing gear retracted aft into the engine nacelles, but the tailwheel was fixed. The nose was extensively glazed to give the bombardier/navigator good visibility and he was armed with a 20mm ShVAK cannon with 10° of vertical travel. The rear gunner/radio operator sat behind the pilot in a manually operated turret armed with a 7.62mm ShKAS machine gun. Two 37mm Shpitalnyi Sh-37 cannon were mounted in the wing roots with very prominent barrels. Up to 600kg (1,300lb) of bombs could be carried internally in the fuselage or a pair of 500kg (1,100lb) FAB-500 bombs could be carried under the wings. It used a pair of 716kW Klimov M-103 inline engines driving 3-bladed propellers.[1]