According to ‘Spread Spectrum Communications Handbook’ vol1:
'In 1935, Telefunken engineers Paul Kotowski and Kurt Dannehl applied for a German patent on a device for masking voice signals by combining them with an equally broad-band noise signal produced by a rotating generator. The receiver in their system had a duplicate rotating generator, properly synchronized so that its locally produced noise replica could be used to uncover the voice signal. The U.S. version of this patent was issued in 1940, and was considered prior art in a later patent on DSSS communication systems. Certainly, the Kotowski-Dannehl patent exemplifies the transition from the use of key-stream generators for discrete data encryption to pseudorandom signal storage for voice or continuous signal encryption. Several elements of the SS concept are present in this patent, the obvious missing notion being that of purposeful bandwidth expansion.
The Germans used Kotowski’s concept as the starting point for developing a more sophisticated capability that was urgently needed in the early years of World War II. Gottfried Vogt, a Telefunken engineer under Kotowski, remembers testing a system for analog speech encryption in 1939. This employed a pair of irregularly slotted or sawtoothed disks turning at different speeds, for generating a noise-like signal at the transmitter, to be modulated/multiplied by the voice signal. The receiver’s matching disks were synchronized by means of two transmitted tones, one above and one below the encrypted voice band.
This system was used on a wire link from Germany, through Yugoslavia and Greece, to a very- and/or ultra-high frequency (VHF/UHF) link across the Mediterranean to General Erwin Rommel’s forces in Derna, Libya.'
After having a look at google patents I saw that Vogt was credited with a patent and I thought that this was the speech cipher system but I was corrected by klausis krypto kolumne commenter ‘Thomas’, who linked the Kotowski-Dannehl patent.
Thus in Rommel’s microwave link I’ve added a link and pics to patent US2211132A.