The P.13B was the next-generation design from the P.13A and was to be a ramjet fighter as well. Designed in late 1944, it also was a delta configuration of 60 degrees wing-sweep, but with turned-down wingtips. Changes to this design resulted in the cockpit being moved to a conventional forward position and double tailfins instead of one vertical tail. On each side of the cockpit on the wing's leading edge were long air intakes to feed the ramjet. Because of the acute fuel shortage in Nazi Germany in the last months of the war (including synthetics), an eccentric plan to use coal (or paraffin coated lignite dust) for fuel was to be attempted (probably the result of Dr. Mario Zippermayer‘s extensive coal dust research as both a fuel and as a weapon). A centrally located round or hexagonal heat-resistant ceramic combustion chamber was to be fitted in the interior of the wing. The main landing gear was a retractable landing skid, with the fuselage resting on the reinforced turned-down wingtips. No armament was planned in the initial stage of development, but 2-4 30mm MK-108s would have been appropriate for the timeframe and role as interceptor. It would appear that this is where the traditional story ends, and that no P.13B was ever constructed, let alone flown to Mach 1 or higher. But declassified evidence has surfaced from the United States and Poland that suggests otherwise.

Assuming that the original intelligence reports are honest, the original evidence is contained in these four primary references: 1) W.Kozakiewicz et al, Bron Rakietowa, publ. Glowny Instytut Mechaniki, 1951 (classified until late 1990s) 2) "Aerodynamics of rockets and ramjet research and development work at Luftfahrtforschungsanstalt Hermann Göring, Volkenrode": CIOS Report Item Nos 4 and 6, File No. XXVII-67 (1946). CIOS=Combined Intelligence Objectives Service. 3) "Survey of German Ramjet Developments" CIOS Final Report, item No.6 File No. XXX-81. 4) NARA/US Strategic Air Forces in Europe - Air Intelligence Summary No. 74 (8.Apr.1946). The American documents contain clear information about airborne trials: "...Professor Lippisch designed an aircraft resembling a bird's wing with ramjet propulsion. The prototype had to be modified continuously. The flying wing was to have a basic speed of 2500 km/hr....to enable the aircraft to reach an adequate speed necessary to start the ramjet, solid propellant rockets were used....the speed was realized by the use of ATO rockets, the airflow heating the coal for more thrust. The hot gases flowed out through the narrow nozzles at the trailing edge. This solution enabled the thrust to be maintained for 45 minutes. In the final months of the war the propulsion effectiveness was doubled by injection of liquid fuel above the coal....." The last sentence means that the aircraft flew. The Lippisch P-13B was described in detail by the American analysts. Their drawings show little difference to the trapezoid version, also illustrated. Since the report mentioned at least two similar versions, it can be assumed that the differences are minor. In the American reports it was stated that the assembly was realized by various facilities of the LFW (Luftfahrtforschung Wien): (i) aerodynamic tunnel at Tülln near Vienna (ii) most elements were built at LFW Wiesenfeld (iii) final assembly LFW Ramsau (iii) above means that the aircraft proceeded beyond the wind-tunnel and was actually constructed. The American reports provide information about the fuel (described). "The American source of information was then cut off in early January 1945 when the prototype P-13B was ready for its first flight. Due to the fact that the Germans expected to achieve the magic speed of 2440 km/hr, the Americans stated that there were many volunteers to make these historic flights."