http://www.ufx.org/german/antiplofer.html

Mystery 1945 German Hypersonic Bomber Prototype?

In the late 1930s, Eugen Sanger, one of Germany's top theoreticians on hypersonic dynamics and ramjets, and his wife, mathematician Irene Bredt, had begun developing a suborbital rocket bomber, "RaBo," (sometimes called the "Antipodal Bomber") that would be capable of attacking targets at intercontinental ranges. Incorporating highly advanced concepts, including swept, wedge-shaped supersonic airfoils, a flat, heat-dissipating fuselage undersurface that anticipated the Space Shuttle's by thirty years, and rocket engines of extraordinary thrust, the RaBo concept would have taken many years to develop -- precious time that was running out for Nazi Germany. In 1944, Sanger and Bredt were moved to a fantastic, isolated laboratory complex in the mountains near Lofer, Austria, where a number of bizarre research projects were underway, including impractical devices such as the infamous "sound cannon" and "wind cannon" and an electromagnetic railgun. Sanger's main known project centered on development of a high-speed, ramjet powered manned bomber interceptor that resembled a stubby missile.

(More at site, including lots of cool period graphics.)