The 509th Composite Group was organized as the weapon delivery arm of the Manhattan Project. Prior to stationing on Tinian Island, the 509th underwent extensive training with modified B-29 Superfortresses at Wendover Army Air Field in Wendover, Utah. It was the 509th that realized Truman's Potsdam Proclamation by inflicting “complete and utter destruction” on Hiroshima and Nagasaki prior to Japan's unconditional surrender.
Representatives of the Army Air Forces and the Manhattan Project first began screening candidates to lead the soon-to-be-formed 509th during the summer and fall of 1944. When the 509th was officially created in December of 1944 it was put under the command of Lt. Col. Paul Tibbets. In terms of military command, the 509th was part of the Twentieth Air Force in the Army.
The group was designated as "composite" because its mission - to drop the world’s first atomic bombs on Japan - was so secret that it required the group to be self-sufficient and isolated. The U.S. Commander in Chief of the Pacific theater was one of many who was not initially informed. Even personnel in 509th B-29 crews and ground support didn't know for what they were preparing. For some time, Lt. Col. Tibbets was the only person in the 509th to know that the ultimate goal was the atomic bombing of Japan.
Tibbets was given complete control over recruitment of personnel. An experienced pilot himself who had flown over twenty-five combat missions in Europe and North Africa, Tibbets largely chose men he had flown with before. Tibbets' squadron initially numbered some seven-hundred men.
Many other groups in the military became part of the 509th. These included: the 390th Air Service Group, the 603rd Air Engineering Squadron, the 1027th Air Material Squadron, the 320th Troop Carrier Squadron, the 1395th Military Police Company, and the First Ordnance Squadron. In total, the group came to include 225 officers and 1542 men.
Many of the members of the 509th had criminal backgrounds. Nonetheless, Tibbets’ men were some of the best pilots, navigators, and flight engineers in the entire U.S. military. Tibbets was able to commandeer men from missions all over the globe. The most important qualities to Tibbets were loyalty and secrecy. He tolerated raucous behavior among his men, so long as he knew they would not tell anyone about what they were doing. Even though they knew very little about what they were training for, members of the 509th were required to remain secretive. Still, Tibetts took no chances: he opened their mail, bugged their quarters, and transferred those that broke security to the Aleutians.
The majority of 509th training took place at a secret base in Wendover, Utah. Because Little Boy and Fat Man were larger than bombs typically dropped from B-29s, the 509th needed practice and special equipment. Bomb release and target aiming were practiced by dropping "pumpkin bombs." High-altitude bombing was a new tactic in 1944, but Tibbets relentlessly drove his flight crews to increase the accuracy of their bomb drops. He also made his crews practice steep diving maneuvers; as this was the only way Tibbets believed a B-29 would be able to escape an atomic bomb's blast. Other training missions took place at Battista Field in Cuba. This is where aircrews practiced coastal and ocean flying, as well as independent navigation.
Tibbets, able to secure anything he needed by citing code word " Silverplate," acquired lighter, more advanced B-29s for the 509th. These had pneumatic bomb doors and were able to taxi backward. The most apparent difference to those outside of the 509th was that these special B-29s, with only one tail-gunner, were much less well-armed.
Security at Tinian
Security for the 509th was, of course, extremely tight. The special B-29s were kept in an isolated corner of the base and access was heavily restricted. Guards, themselves unaware of the importance of what they were protecting, were authorized to shoot anyone who tried to get too close to the B-29s. Even generals were not allowed to approach the planes. The island buzzed with rumors as a result. One Japanese Imperial Staff report, in reference to the 509th, stated: "One other unit is available but its identity has not been ascertained yet." Until Hiroshima, Japan had no idea what it was facing.
Before this, they also operated combat missions starting June 30, 1945 to prepare the pilots and planes for their atomic mission. They dropped bombs on Japanese controlled islands throughout July to practice radar and visual bombing procedures, in addition to dropping pumpkin bombs in Japan, and practice missions with inert Little Boy and Fat Man prototypes.
Silent film showing the loading of the Little Boy into Enola Gay on Tinian on August 6, 1945. Video courtesy of the Naval History and Heritage Command.