 His most significant contribution in this area was the idea of using a blunt nose for reentry vehicles, otherwise known as his "Blunt Body Theory".Earlier ballistic missiles, developed by both the United States and the Soviet Union, featured long nose cones with very narrow tips, which had relatively low drag when entering the atmosphere at high speeds.However, Allen demonstrated that a blunt body, although it had greater drag, would have a detached shock wave which would transfer far less heat to the vehicle than the traditional shape with its attached shock wave.