Tupolev ANT-16 (also known as TB-4; – Heavy Bomber) was an experimental heavy bomber aircraft designed and tested in the Soviet Union in the early 1930s. Conceptually representing evolution of the TB-3 bomber, ANT-16 was designed under the doctrine that size and payload were more important for a bomber than speed because it would be able to protect itself with defensive armament. The twin 5×1.8×1.8 m (16 ft 5 in × 5 ft 11 in × 5 ft 11 in) bomb bays were the largest in the world at the time and presented many design challenges in order to preserve structural rigidity of the airframe.