The stresses of military deployment were naturally a consideration for Wasserfall too, but its integral tank structure could more easily bear higher loads, because von Braun’s engineers had decided to return to pressure-fed engines. As in the A-5 and earlier rockets, compressed nitrogen would force the propellants into the combustion chamber, making the missile simpler and more capable of prolonged storage in the field; the complicated turbopump/steam-generator system could be eliminated. The number of valves would be reduced as well by employing special bursting membranes that would be blown open when a charge was fired to open the nitrogen tank. In principle, the triggering of the charge would result in the automatic opening of the pipelines to the engine, followed by ignition and liftoff.
The preliminary design phase, through the year 1943, thus went fairly well. Pursuant to it request by von Braun and his engineers, who had learned a lesson from the troubled history of the A-4 and the Peenemünde Production Plant, the missile was also made easier to manufacture by bringing the advice of an experienced firm into the project. At the May 1943 “comparison shoot,” Field Marshal Milch announced that Henschel, which had built rocket-assisted glide bombs and was designing its own anti-aircraft missile, the Schmetterling (Butterfly), would act as a consultant. By autumn Henschel designers were able to suggest useful modifications that would facilitate mass production.77
The one clear trouble spot was personnel. At the end of 1942 the air force had formed a special unit, the Flak Experimental Center Peenemünde (later Karlshagen), to staff the Wasserfall project and the new test stands being built for it. The center paralleled the Army’s Northern Experimental Command in that it could pull Luftwaffe personnel from other units and assign them to Peenemünde-East. This unit, which was not formally connected to the air force’s own base at Peenemünde-West, had another dimension as welclass="underline" Its headquarters staff served as a sort of supervisory office for Wasserfall. The growth of the Flak Experimental Center was slow, however, because other Luftwaffe units obstructed transfers. Moreover, in the summer of 1943 Milch became furious when he found that Luftwaffe personnel assigned to the Army had been pulled into A-4 work. Because of the extreme pressure to produce results, Peenemünde had clearly exploited the interservice project to prop up the ballistic missile program.78
Those troubles aside, however, Wasserfall appeared to be proceeding satisfactorily until January 1944, when the missile’s optimistic schedule collapsed. At the end of that month Ludwig Roth wrote a memorandum to his boss, design bureau chief Walther Riedel, indicating how unrealistic was the Air Ministry’s requirement for the delivery of a complete set of Wasserfall production drawings by April 15. That deadline had been advanced a month on Milch’s promise that more draftsmen and designers would be detailed to Roth’s office; some indeed were. But even May 15 was Utopian. Roth outlined a number of serious development problems, such as difficulties welding the interface between the wings and the tank structure, but the most fundamental were the choice of a fuel and the guidance system’s lack of definition.79
The propellant problem arose from a lack of capacity in the chemical industry, caused, in all probability, by Allied air raids and the Armaments Ministry’s lukewarm support for the anti-aircraft missile program. As a result, there was no adequate supply of Visol for the deployment of hundreds of Wasserfalls and other defensive missiles by late 1944, the expected date. The Visol would have to be mixed with other chemicals, but that implied the expenditure of further research time to find a combination with the same performance. A new fuel combination would also change the density of the propellant and would therefore alter the mixture ratio between it and the nitric acid oxidizer, which itself had been cut with sulfuric acid to lower combustion chamber temperature and prevent engine burnthroughs. An uncertain mixture ratio threw into doubt the relative size of Wasserfall’s two main tanks, which necessarily brought into question the entire structural design of the missile. Only in the summer of 1944 was Peenemünde able to settle on a fuel combination that performed well and had the same density as pure Visol, thereby salvaging the existing tank design.80
The difficulties with guidance and control were even more fundamental. As Roth noted, even such a basic problem as the creation of a sufficiently powerful control system was unsolved. The need for the missile to maneuver imposed much more demanding requirements on the vane servomotors, which had to exert and resist greater aerodynamic forces than the same systems on the A-4. The program’s attempt merely to modify the existing Luftwaffe mass-produced hydraulic servomotors proved to be a failure, and substitute electrical servos were slow in coming. Further development would be required for both types, with the result that it was impossible to say in early 1944 what the final design of the Wasserfall control system would look like, or even which principle the servomotors would use. A final layout of the missile’s tail section was therefore impossible.81
The situation in guidance toward the target was even worse. From the outset, it was assumed that the final Wasserfall guidance system would be based upon a modification of one of the existing “Giant” radars into a guide beam that would slowly turn the vertically launched missile in the direction of the enemy aircraft and bring it into the target’s vicinity. In the autumn of 1942 von Braun still believed, on the basis of information from Luftwaffe and industry experts, that the accuracy and discrimination of those radars would allow the guide beam to direct the missile to the target, whereupon a signal could be sent to trigger the warhead at its nearest approach. He and his informants significantly overestimated the capability of the radars, however, particularly in the case of a bomber stream, where they were unable to distinguish individual aircraft. Von Braun was nevertheless aware that a homing device in the missile would be desirable; by 1943 it became increasingly apparent that it would be a necessity if the missile was ever to come sufficiently close. Yet even the physical principle of a workable homing device was debatable in 1943–44, although infrared (heat-seeking) systems seemed the most promising.82
In addition, the insufficient discriminatory capability of radar meant that Wasserfall needed a proximity fuse to trigger the warhead in the likely event of a near miss. Yet no such fuse was available. The United States was able to deploy a such a fuse on anti-aircraft shells in 1944, but only after a massive program to develop a miniature radar set that could withstand the shock of being fired out of an artillery piece. German resources were spread too thin to permit a similar success. Proximity fuse projects, like those to build homing devices, were started too late and were allowed to proliferate without adequate control from the Air Ministry, with the result that none produced a workable device during the war. Even with better management, however, it is unlikely that the Germans could ever have deployed enough proximity fuses or homing devices to affect the military situation even marginally, given their inferiority to the Allies in research and development resources and electronic technology.83