Douglas XB-31 (Raidmaster) (Model 332) Super-Heavy Bomber Aircraft Design Proposal
The Douglas XB-31 super heavy bomber was proposed against the Boeing XB-29, the Lockheed XB-30, and the Consolidated XB-32 - it was not furthered beyond a design study.
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The Douglas XB-31 "Raidmaster" became one of four submissions passed along to the United States Army Air Forces (USAAF) during World War 2 (1939-1945) attempting to fulfill a requirement for a new long-range, high-altitude "super heavy bomber". The requirement was eventually filled by the Boeing B-29 "Superfortress" with Consolidated's XB-32 selected as an insurance measure (this becoming the B-32 "Dominator"). Before the decision was made, the XB-31 competed against the Boeing submission as did an entry from Lockheed (the XB-30, detailed elsewhere on this site) - both were removed from contention in time.
Origins of the XB-31 lay in the late 1930s when American authorities realized advancements being made in military aircraft in Europe (particularly Germany) were beyond anything that was had in the current inventory. A committee was arranged by the Army for direction and the consensus was to pursue a new very-heavy, long range bomb delivery platform. The outbreak of war in Europe during September 1939 only served to put an emphasis on getting the large aircraft into the sky in short order.
The requirement called for exceptional range and excellent operating altitudes, the latter to help keep the system as far away from enemy interceptors and ground-based fire as possible. Speed was also essential as was a competent bomb load to make the product worth its investment. To this point, the standard heavy bombers in the American stable were the Boeing B-17 "Flying Fortress" (introduced in 1938) and the Consolidated B-24 "Liberator" (introduced in 1941) - both classics in their own right but eventually outmoded by the advancing nature of the war.
As such, work proceeded on finding their successor - Boeing held a head start on their XB-29 product and eventually won the contract. In 1940, Douglas readied theirs through the "Model 332" initiative to which the U.S. Army designation became "XB-31". On paper, the Douglas submission already surpassed the other three entries in terms of size and operating weight - a mammoth design to be sure.