In response for the Army's request for a large, multiengine bomber, the B-17 (Model 299) prototype, financed entirely by Boeing, went from design board to flight test in less than 12 months. The first B-17s saw combat in 1941, when the British Royal Air Force took delivery of several B-17s for high-altitude missions. As World War II intensified, the bombers needed additional armament and armor. Each version of the B-17 was more heavily armed than its predessor, and in the Pacific, the planes earned a deadly reputation with the Japanese, who dubbed them "four-engine fighters."