A-4b Rocket (Germany) ICBM

In anticipation of the possibility that launch sites might be forced back into the Reich itself, von Braun and his colleagues were put under pressure to develop a longer-range version of the A4 known alternately as A9 and A4b, the reason for the dual designation being that the A4 series had received "national priority"; the A4b designation ensured the availability of scarce resources.

In June 1939, Kurt Patt of the Peenemünde Design Office, proposed wings for converting rocket speed and altitude into aerodynamic lift and range. As the rocket encountered thicker atmosphere on its descent phase, it would execute a pullout and enter a shallow glide, trading speed for distance. Patt also proposed the Flossengeschoss (fin projectile). Both concepts were utilized by Walter Dornberger when he drafted a memo for presentation to Hitler regarding the "America rocket" on July 31, 1940.

Design studies on the A9 began in 1940. In addition to its wings, the A9 would have been somewhat larger than the A4 and its engine would have produced about 30% more thrust. Following wind tunnel testing of models, the design was subsequently modified to replace the wings with fuselage strakes, as the tests showed that these provided better lift at supersonic speeds and also solved the problem of transonic shift of the centre of lift.

Development was suspended in 1941, but in 1944 several V-2s were modified to an approximation of the A9 configuration under the designation A4b.[25] It was calculated that by fitting wings, the A4's range would be extended to 750 km (470 mi), allowing targets in Britain to be attacked from launch sites within Germany itself. It was intended that following launch the curve of the A4b's trajectory would become shallower and the rocket would glide toward its target. It was anticipated that interception by enemy aircraft at the end of the glide phase would be virtually impossible as over the target the A-4b was intended to enter a near vertical dive leaving little time for interception.

The A4b concept was tested by fitting swept back wings to two A4s launched from Blizna. Little development work had been carried out and the first launch on 27 December 1944 was a complete failure. The second launch attempt, on 24 January 1945, was partially successful, in that the wing broke off, but the A4b still managed to become the first winged guided missile to break the sound barrier and attain Mach4.