One of the first North American B-25s built. (U.S. Air Force photo)
The pace of U.S. bomber development accelerated through the 1930s into the World War II years. Projects on the drawing board in the late 1930s were built and flying by the early 1940s. These projects could be grouped into three broad development categories: medium bombers, very heavy bombers and special projects.
The two most famous medium bombers were the North American B-25, which was developed using knowledge gained in the unsuccessful XB-21 project, and the B-26, the first successful Martin bomber since the ground breaking B-10.
At dawn on April 18, 1942, a U.S. Navy task force was heading through rough Pacific seas toward Japan. One of the ships in the flotilla was the aircraft carrier Hornet with 16 AAF B-25s on deck. Plans called for the B-25s to take off from the carrier within 450 to 650 miles of Japan, bomb selected targets at such locations as Yokohama and Tokyo, and then fly another 1,200 miles to friendly airfields on mainland China.
AAF B-26 medium bombers in England became operational in the spring of 1943. Not having the long range of the B-17 and B-24, B-26s were used almost exclusively for missions to Holland, Belgium and northwestern France, where they bombed airfields, transportation and lines of communication.
Very heavy bomber development can be traced back to the Boeing XB-15 and Douglas XB-19. Although neither design was successful, the data gathered led to the development of the B-29 -- one of the best bombers of WWII.
Development of the Boeing Superfortress, "very heavy bomber," began late in 1939 and the first XB-29 made its initial flight on Sept. 21, 1942; however, in a bold wartime gamble, the AAF ordered the plane into quantity production months before this first flight. Among the B-29's new features were pressurized crew compartments and a central fire-control system with remotely controlled gun turrets. Flying combat missions first from India and China and later from the Marianas Islands, the Superfortress repeatedly demonstrated its capability for carrying bomb loads of up to 20,000 pounds against targets as far away as 1,500 miles from its base.
Even larger bombers were in development during the war. The prototypes for the Northrop B-35 flying wing and the massive Consolidated B-36 Peacemaker were both ordered in 1942.
Finally, some bombers series were modified to test the feasibility of the escort bomber concept. Because of the limited range of escort fighters early in the war, bombers with greatly increased armament were built. The plan failed mainly because the increased weight of the escort bomber made it too slow to keep pace with the regular bomber formation and it had no maneuverability to avoid enemy fighter attacks.
