Heavy bomber
Heavy bombers are bomber aircraft capable of delivering the largest payload of air-to-ground weaponry (usually bombs) and longest range of their era. Archetypal heavy bombers have therefore usually been among the largest and most powerful military aircraft at any point in time. In the second half of the 20th century, heavy bombers were largely superseded by strategic bombers, which were often smaller in size, but were capable of delivering nuclear weapons.
Because of advances in aircraft design and engineering — especially in powerplants and aerodynamics — the size of payloads carried by heavy bombers have increased at rates greater than increases in the size of their airframes. The largest bombers of World War I, the four engine aircraft built by the Zeppelin-Staakencompany in Germany, could carry a payload of up to 4,400 pounds (2,000 kg) of bombs. By the middle of World War II even a single-engine fighter-bomber could carry a 2,000-pound (910 kg) bomb load, and such aircraft were taking over from light and medium bombers in the tactical bombing role. Advancements in four-engine aircraft design enabled heavy bombers to carry even larger payloads to targets thousands of kilometres away.