The DIII Telephone was used in World War 1 as a normal field telephone and also as a morse telegraph system. It was used in dugouts, and it was small and portable enough, to enable it to be carried into forward areas, and used for artillery observation. It was supplied in a leather pouch with a shoulder strap. There are two compartments, one for the morse key and buzzer unit, and one for the telephone handset. There was a separate earpiece for monitoring. The leather top could be opened, allowing normal use of the key or handset. The top could be closed, and the side lifted up, to enable use of the morse key by individually.
Figure: DIII front
The leather pouch is embossed D. MASON & SON, BIRMINGHAM 1918. Some pouches were made by Martins Ltd as well. It also has 2 initials scratched into the leather, which appears to be “JR”.
The leather pouch is divided into 2 compartments. One contains the handset. The other compartment has a small metal box that has several terminals and a morse key. The panel lifts up, and reveals a buzzer and a capacitor. The top of the case is stamped, as being “not earthed”. This may overcome any ground loop or earthing problems.
Figure: Buzzer unit
The case is stamped DIII**, but the ** appears to have 2 strike out lines through them. There is also the lettering STERLING 127844 and 1918.
The buzzer is attached under the ebonite panel, which holds the morse key. There are two adjustments on the buzzer, labeled No1 and No2.
There is an instruction plate attached to the leather pouch, which provides a step-by-step adjustment procedure.
Figure: Instruction Plate
There is another plate next to it, which shows the phonetic code, in use during World War 1. Notice that it is different to the modern phonetic code.
Figure: Phonetic Code
The handset is unique. It has a fold up metal flap, to protect the carbon microphone, and possibly to act as an ambient noise attenuator. The ear piece is a normal dynamic type. The handset has a telescopic handle so that it can be shortened to allow it to fit into the pouch. There is a Push-to-Talk switch which enables the microphone. The cord is covered in a brown woven cloth, and is fraying at the handset end.
Figure: Handset (extended)
Figure: Handset (collapsed)
The phone was in good overall condition. The leather was in excellent condition, the buckles and the strap are still very flexible. The buzzer unit has no rust on the outside and did not need repainting. The wiring and the condition of the internal buzzer were very good. The battery compartment was clean, and there was no evidence of a battery ever having leaked in there.
I located an X-cell, which fitted the square battery compartment. It is slightly different, in that it has two terminals on the top, whereas it appears that the correct cell for this phone uses a side contact and a top contact. Alternatively, perhaps I could slip a plate down the side, and then connect the terminals. I temporarily fitted two D cells in series, and powered the buzzer. It initially did not work. I cleaned the contacts, then followed the adjustment procedure on the instruction plate, where upon, it started working.
The handset was missing, but I luckily had one in my box of handsets. I tested this, and then fitted it to the unit. When speaking, I could hear sidetone, and also see a reasonable waveform on an oscilloscope. When the key was pressed, the buzzer tone was audible.
This is a very simple field telephone and telegraph unit, in a lovely leather case. It appears to work quite well.