Douglas D-558-2 SkyrocketDouglas D 558 2 Skyrocket airplane model. The Skyrocket made aviation history when it became the first airplane to fly twice the speed of sound. The II in the aircraft's designation referred to the fact that the Skyrocket was the phase two version of what had originally been conceived as a three phase program, with the phase one aircraft having straight wings. The third phase, which never came to fruition, would have involved constructing a mock up of