The B-29 was also unsuitable as it had two 12 foot bomb bays divided by the wing main spar box. The B-24 appeared to be a candidate but the Navy had failed to convert the aircraft to accomodate a torpedo in the bomb bay, so an atomic bomb wasn't going to work any better. Early requirements estimated a weapon that would be 17 feet long and weigh over 10,000 pounds. Dubbed 'Silverplate', the search was on for a suitable aircraft. Even as the Manhattan Project moved forward, a parallel program was launched to find a bomber which could deliver an atomic bomb should the folks at Los Alamos succeed.
Germany was working on their own atomic weapon which led to some famous bombing raids to delay their program. Most folks remember the 'Manhattan Project' which was the super-secret program to develop the first atomic bomb.
