During the closing weeks of World War II, the German work at Peenemünde was investigated by Soviet intelligence, amongst whom was rocket motor constructor Aleksei Isaev, who found a copy of Sänger and Bredt's report.
[2] In November 1946 the NII-1 NKAP research institute was formed with mathematician Mstislav Keldysh as its head to investigate and develop the German Sänger–Bredt design.
However, use of a rocket driven slide for the takeoff run and ramjets during the atmospheric acceleration phase would be more efficient than the original concept and could give the craft a more reasonable 22% dead weight and still achieve the 5 km·s−1 velocity required for a 12000 km intercontinental range.
The mission would be started using five to six rocket engines RKDS-100, burning LOX/Kerosene and driving a sled including the bomber mounted on top with a total thrust of 5 to 6 MN running on a 3 km long track.
After horizontal acceleration with approximate 5 g for about 10 to 11 s up to a speed of 500 m/s the craft would separate and lift off, still driven by its single on-board RKDS-100 rocket engine delivering about 1 MN thrust, but now supported by two more fuel efficient wingtip mounted ramjets.