These big bombers were designed and built with the single purpose of destroying the Japanese Empire. The B-29 entered service in October 1944, and for the next nine months, relentlessly hammered the huge industrial targets on the main island with both explosive and incendiary attacks. The result was some of the greatest firestorms the world had ever seen, and the biggest human casualties caused by air attack. Before production ended, 3,960 B-29 Superfortresses rolled off the assembly lines.