The Warfare Aeronautics DS-3 "Toucan" was a heavy class starfighter designed to usually carry and launch spy satellites from Earth to Space. But as the IIIrd Interstellar War broke out, there was no spacecraft powerful enough to strike down alien big destroyers. That's why the biggest airborne atomic missile ever conceived was created. As this AWG-33 missile was very sensitive to heat, it had to be carried inside a bay before being launched. So the choice was quite obvious and consequently the "Toucan" was modified to shoot it.