Example of the complete German WWI Field Telephone

Thanks to Bob Norman for the photo. If you want any medals or pictures framing he's your man. Change the $ to @.

The bit I've got is the wooden box behind the handset. If anyone's got any other bits for my collection I'd like to hear from them!

This is the British equivalent.

A WWI Army Field Telephone in context.

This is an amplifier made by the same firm that designed the cryptographic equipment whose key was cracked by the Enigma computer at Bletchley Park some twenty odd years and a war later.

When a telephone was used to signal from a WWI trench an earth connection was usually made and through the earth connection a signal flowed into the ground. The majority of the signal took the easiest path between sender and receiver but lots of current also passed by more roundabout routes. Because trenches rarely followed straight lines anyway a good proportion of the earth current was detectable at nearby German trenches and if connections were made to ground at two widely separate points enough of the current was available to drive a sensitive detector. The amplifier shown used four triode valves and was able to amplify tiny intercepted earth currents sufficiently for an eavesdropper to listen in on enemy communications.

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