The Feldfernsprecher 33 (FF33) was the most commonly used field telephone by the Wehrmacht during World War 2. It was first developed in 1933 and lasted in production until early 1945.
The FF33 is an OB (Ortsbatterie Betrieb) telephone, that is, it uses a 1.5 volt onboard battery to power the handset microphone. It also has a crank magneto to generate ringing current. It was designed to be used in the battlefield with the lid closed to make it reasonably water resistant. The handset cord and telephone lines extend through rubber seals where the lid comes together with the body.
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WW2 German Field Telephone Equipment 