Boeing YB-40 Flying Fortress Boeing YB-40 Flying Fortress The Boeing YB-40 Flying Fortress was a modification for operational testing purposes of the B-17 Flying Fortress bomber aircraft, converted to act as a heavily armed gunship for other bombers during World War II. At the time of its development, long-range fighter aircraft such as the North American P-51 Mustang were just entering quantity production, and thus were not yet available to accompany bombers all the way from England to Germany and back. Work on the prototype, Project V-139, began in September 1942 by converting the second production B-17F-1-BO (serial number 41-24341) built. Conversion work was
American Theater (World War II) other heavy bomber projects were cancelled. During the final months of World War II, Japan had planned to use plague as a biological weapon against U.S. civilians in San Diego, California, during Operation Cherry Blossoms at Night. The plan was set to launch at night on September 22, 1945. However it was shelved after Yoshijiro Umezu, Chief of the Imperial Japanese Army General Staff, rejected it. Additionally Japan surrendered five weeks before the plan had been intended to take place. These false alarms have generally been attributed to military and civilian inexperience with war and poor radars of the era.