Zeppelins
1916 Spark Transmitter, which was originally fitted to an airship, where it produced sparks within a few feet of the (usually leaking) hydrogen filled gas bag.
Another aspect of the unseen electronic wireless war was that the L59 Zeppelins raiding Britain used radio signals as a navigational aid. Wireless telegraphy systems had always comprised an important part of the equipment of Zeppelins (and French dirigibles). They were able to carry much greater transmitting power, due to a larger space available which combined the use of a larger antennae system gave much greater ranges than other aircraft.
By
mid April 1915, it was discovered that if a Zeppelin transmission
included the words 'only HVD on board' it indicated that the airship
was bound for Britain and was not on a routine reconnaissance over
the North Sea.
HVD was the German navy code book for signalling
merchant ships and was known to be compromised and was thus the only
code book allowed to be carried over Britain.
Both British and French stations attempted to jam the Zeppelins navigation by transmitting on what they assumed would be same frequencies. It was then found that the German aircrew were actually using the French transmissions from the Eiffel Tower to provide their navigational fixes. On the night of the 19/20th October 1917, during a major Zeppelin raid on Britain, transmissions from the Eiffel Tower were simply switched to another station.
The effect was to give the German navigators completely false bearings. The returning Zeppelins were all badly off course, two ending up in the South of France and five were destroyed or captured. The use of wireless to mislead was kept top secret and as the weather was bad that night with strong winds this was given out as the reason for the disaster.