The main German field communication device was the Field Phone model 1933 or FF33. This wired telephone was used throughout the war in favor of wireless communicaitons which were more easily intercepted and which could be used for enemy target detection by the allies. The 1933 modelof field phone was a self contained phone in a bakelite box. The fittings were initially unpainted aluminum but were later changed to black painted steel. Near the end of the war a simplified field phone was introduced but this was for intents and purposed interchangeable with the FF33. Field phones could be strung from one to another by means of two wires which could be attached on each end to terminals on the phones. If the crank was turned on one end an electrical charge would be sent to the other end and rang a bell. The receiver then picked up the handset like normal telephone. If the send switch was depressed the handset could be used for voice communication. Voice communication required battery power to send. In the case where the battery was dead or missing on one end the phone would still be able to receive the sound but not send its own. Multiple field phones could be hooked together by means of a switchboard. 

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These photographs and information were taken from a number of online sources and auction sites.  They are presented here for educational purposes.