Michael Neufeld - The Rocket and the Reich

By late 1940 Hoelzer and his assistant, Otto Hirschler, had managed to develop such a device. Beam testing was done with aircraft flying out across the Baltic to the occupied Danish island of Bornholm. Steinhoff piloted many of the flights himself. Even with that experience, perfecting a stable and workable system to be tested on the A-5 was difficult, and the first launch was not attempted until the spring of 1941. After working out innumerable problems in A-5 and A-4 launches, this guide beam was later used in some launches in the V-weapons campaign. 59

The true significance of Hoelzer’s work, however, lay elsewhere. By mid-1941 repeated launches with the A-5 had shown that stable flights could be achieved with all three control systems: Kreiselgeräte, Siemens, and Askania/Möller. But scaling up these systems for the A-4 presented new problems. The vehicle would be much larger, as would the aerodynamic forces; therefore the demands on the control system’s vane servomotors would be much higher. Kreiselgeräte’s elaborate systems of electrical motors and gears was inadequate to the task, and Möller’s electric motors were inferior to Siemens’s hydraulic systems. Even a hydraulic system might not be stable, however. Experiments with the engines running on the first static-test A-4s in the summer and fall of 1941 showed that the existing systems were indeed of questionable stability. Months more development and lots more money would be needed. 60

In this critical situation, Hoelzer’s “mixing device” provided the answer. By modifying it to take signals from the position gyros, the rate gyros could be eliminated altogether and the missile made stable. That crucial innovation was possible because, in his work for the guide beam mixing device, Hoelzer had to develop circuits for the mathematical operations of addition, integration, and differentiation. By differentiating the position signals from the gyros—that is, how they changed over time—it was possible to determine the turning rate of the missile in each axis. Thus rate gyros were unnecessary. With the calculation possibilities of this clever device, other stability terms could also be more easily introduced into the correction signals sent to the vane servomotors. Furthermore, the ratios of the various signals could be changed during engine firing to compensate for the changes in aerodynamic forces and missile characteristics. Finally, the elimination of the very expensive rate gyros meant large potential cost savings on a mass-produced A-4, which was becoming an urgent concern in 1941. The tradeoff was the need for more electronics, especially vacuum tubes, which were in short supply in the German war economy. 61

Hoelzer’s mixing device spawned yet another brilliant invention: one of the world’s first fully electronic analog computers. He needed only to develop circuits for a few other mathematical operations to create such a computer. Beginning in 1942 his staff built one in the guidance and control laboratory for calculating and simulating A-4 trajectories. It could do in minutes what human “computers,” typically women working with mechanical desk calculators, took weeks to accomplish. Hoelzer’s computer added one more tool to the increasingly sophisticated simulation techniques pioneered by Peenemünde to overcome the vexing problems of ballistic missile guidance. But it was the application of the mixing device to the rocket’s control system, not computer simulation or guide beam work, that proved to be the truly critical innovation developed by Hoelzer’s group. Without it, an operational A-4 would have taken longer to develop and would have been more difficult to produce in large quantities. 62

With the mixing device solution in late 1941, a final major piece had fallen in place for the creation of truly guided missile. By no means, however, did Steinhoff’s division have a complete working guidance system. The limitations of A-5 flights and simulation techniques left many unknowns. Furthermore, the configuration of a feasible system was only beginning to jell. Launches with the Kreiselgeräte’s Sg 52 beginning in October 1939—the first successful guided flights—and with Siemens and Askania/Möller systems starting in April 1940, had demonstrated that there were at least two feasible solutions to the gyro layout. Kreiselgeräte’s stabilized platform was inherently superior in accuracy, but was complicated and expensive in comparison with the alternatives. The company also lacked capacity to manufacture a more advanced new version for the A-4 (the Sg 66) in large numbers. The second best solution was Fieber’s “Vertikant guidance,” with two rocket-fixed position gyros, because it used the lowest number of expensive components. It was tested in limited ways with both Siemens and Askania equipment on A-5s. Those flights demonstrated the superiority of the hydraulic servomotor over Möller’s electric motors as well. 63

The great difficulties in acquiring sufficient manpower at Siemens and the resulting delays in production had resulted in alienation between Altvater’s division and Peenemünde. Because the Reich had the right to use Fieber’s patent, the rocket group transferred development of the appropriate gyros and vane motors to Askania and the old gyroscope firm of Anschütz. Only the rapidly growing in-house development capability of Steinhoff’s division—another consequence of the dramatic expansion of the Ordnance facility—allowed the Peenemünders themselves to take the lead and to mix components for the A-5 and A-4 from all three firms, as appropriate. Instead of being the developer of the Vertikant system, Siemens became just another contractor. 64

Thus, on the eve of the first A-4 launches in 1942, it cannot be said that Steinhoff’s guidance and control laboratory had a clear idea of what system would become the final one. Indeed, it would have been foolish to be sure of success. But the elements were there: one of two gyro arrangements, a mixing device, hydraulic vane servomotors, a radio or accelerometer engine-cutoff device, and possibly a guide beam. Considering how far from a long-range guided missile the Army rocket group had been only four years before, after the failure of the A-3s, this was a stunning achievement. Together with the eighteen-pot, 25-ton-thrust engine and the refined aerodynamic configuration of the A-4, the creation of missile guidance by Peenemünde had laid the foundations for a technological revolution in rocketry.

How could that revolution have been accomplished in five short years? A strong foundation had clearly been laid before 1936 by von Braun’s group, and his charisma, intellect, and management talent continued to exercise a powerful influence thereafter. University research, especially after the war-induced loosening of security in September 1939, added another critical dimension. The key factors, however, were the investment of massive resources and Dornberger’s government-dominated “everything-under-one-roof” concept for Peenemünde. Even when Ordnance tried to hand a problem over to corporate contractors, as in the case of guidance and control, industry’s lack of capacity, interest, or technological capability had forced the rocket program to hire more specialists for its own staff. The resulting concentration of talented engineers in one place, under the inspired leadership of von Braun, Thiel, Hermann, and others, created a fruitful interaction of minds. Of course, brilliant ideas alone were not enough. Money, matériel, and manpower were needed to convert key innovations into working technologies. Massive expenditures on new facilities and personnel at Peenemünde were therefore required. The sheer size of those investments naturally contributed a great deal to speeding up development, but the “everything-under-one-roof” concept also helped to eliminate some of bureaucratic paperwork and delays created by contracting. Much testing and experimentation could be done in-house as soon as it was needed. 65