Manufactured in the autumn of 1943, the NB (Nochnoi Bombardirovshchik - night bomber) prototype had been designed at the Polikarpov Design Bureau and was given the factory designation 'T'. It had refined aerodynamics, a twin-fin empennage and high capacity bomb bay, and its overall dimensions were practically the same as those of the production Ilyushin II-4, though its flying weight and bomb load were significantly greater. The bomber's structure incorporated several innovations, and it had a crew of five. A 4,409 lb (2,000kg) bomb load was attached to special carriers in the bomb bay, and externally mounted bombs brought the total bomb load to 1,102 lb (5,000 kg).
   The NB's powerplanl consisted of two 1,850 hp (1,380kW) ASh-82FNV air cooled engines. Variants were projected powered by 2,000 hp (1,492 kW) ASh-71s and water cooled AM-39s. Its armament consisted of a fixed 12.7 mm UB machine gun mounted in the nose, one UB in an upper turret, and another machine gun in a lower hatch mount.
   The maiden flight of the NB(T) look place on 23rd May 1944, and manufacturer's tesls began in August. The bomber attained a speed of 316 mph (510 km/h) at 16,400 ft (5,000 m), which wasrathergoodat that time. Consequent upon Nikolay Polikarpov's death the tests were not completed and development work ceased.