Warbreakers - Radio Research

Since one of the key feature of any german vehicles is going to be the radio equipment (either transmitter or reciever), I did some research on what radio equipment of both WW1 and the 1920s looked like (the later date because you can get away with a lot by claiming someone was ahead of their time)

Reciever to allow Radio Control of  a battleship

Interestingly, there appears to be a strong tendancy towards sturdy wooden boxes for containing the apparatus, which gives a starting point for any personal transmitters; Valves also appear to be a recurring theme, and seem to offer a nice visual flourish.