B-29 Superfortress, Vol. 1: Boeing's XB-29 through B-29B in World War II. David Doyle. 9" x 9". The Boeing B-29 Superfortress was not only the largest and most advanced US aircraft to see combat in World War II, it was also the most expensive weapons system of the war, even exceeding the cost of developing the atomic bomb—the weapon that ultimately would be delivered to Hiroshima and Nagasaki by a pair of B-29s in August 1945.