These are Army field phones made in 1939 and 1940, with numerous Waffenamt stamps on the various components. This phone is called the "Feldfernsprecher M33" or field phone model 33, indicating it was designed in 1933. They have a hand-crank generator to ring a bell in the remote phone and use battery power for the microphone. A single modern D cell battery works great. Keeping the button depressed on the handset allows full duplex operation, the user can hear and talk at the same time. The microphone inside the handset also has the famous green cross. The German, US and Japanese field phones all work interchangeably.
Pictured is the 1939 phone, but both are essentially identical. The 1939 phone has serial number 13,968 and the manufacturer's mark looks like NT. The 1940 phone has serial number 13,997 with a manufacturer's mark of CM.
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