509th Composite Group Wendover Army Air Field Colonel Paul Tibbets combat group Great Bend, Kansas Mountain Home, Idaho pumpkin bombs code name War Department Tinian
The 509th Composite Group was constituted on 9 December 1944, and activated on 17 December 1944, at Wendover Army Air Field, Utah, commanded by Colonel Paul Tibbets. Tibbets was assigned to organize and command a combat group to develop the means of delivering an atomic weapon against targets in Germany and Japan. Because the flying squadrons of the group consisted of both bomber and transport aircraft, the group was designated as a "composite" rather than a "bombardment" unit. Due to its remoteness, Tibbets selected Wendover for his training base over Great Bend, Kansas and Mountain Home, Idaho. Each bombardier completed at least 50 practice drops of inert or conventional explosive pumpkin bombs, targeting islands around Tinian and later the Japanese home islands, until as late as August 14, 1945. Some of the missions over Japan were flown by single unescorted bombers with a single payload in order to accustom the Japanese to this pattern. They also simulated actual atomic bombing runs, including the directions of ingress and egress with respect to the wind. Tibbets himself was barred from flying most missions over Japan for fear that he might be captured and forced to reveal what he knew. On 5 April 1945, the code name Operation Centerboard was assigned. The officer responsible for its allocation in the War Department's Operations Division was not cleared to know any details of it. The first bombing was later codenamed Operation Centerboard I, and the second, Operation Centerboard II.
