With the successful test of Trinity, final preparations for the bomb's use on Japan were being made. For the past year, the 509th Composite Bomb Group, under command of Col. Paul Tibbets, had been preparing for the mission at a secluded air base in Wendover, Utah.
On June 10, 1945, the 509th Bomb Group and their new B-29 bombers arrived on Tinian, located 1,500 miles southeast of Japan. It was chosen because of its long runways, which the heavily loaded bombers would require for take-off.
The components of the bombs had been sent by cruiser to Tinian in May and the fissionable material was flown out in mid-July. The two atomic bombs were assembled on Tinian, with final assembly to be done in flight.