A standard field telephone instrument used rear of Div. H.Q. for speech communication only.
For a reliable speech using D.8 twisted cable 10-12 miles and using D.3 twisted cable 8-10 miles, providing cable is in good condition and has a minimum number of well-made joints.

This instrument is "sound powered" and requires no batteries.
Used by Coast Artillery A.A. Searchlight Batteries, for medium distance intercommunication and in theatres where battery supply is difficult to maintain due to extreme climatic conditions.
The Handset used, "Telephone hand H" contains a special type of capsule, which is used both in the microphone and receiver. The capsule work on the moving armature principle and require no power supply from the batteries, as they actually produce an E.M.F. which varies according to the sound waves striking the diaphragm.

A light portable field telephone instrument built into a metal case and suitable for use in Div. H.Q. and forward area. Unlike telephone set F this instrument has no cradle switch, therefore the handset carries a switch.
In addition to speech communication this instrument provides for Morse communication by buzzer and key.
Using "cable electric D.8 Mk III twisted", reliable telephonic communication will be obtained up to 10-12 miles. Telegraphy using the same cable, about 25 miles.

A very light portable telephone set, built into a metal case, the top of which can be closed in bad weather without interference with the use of the instrument. Primarily intended for use by linesmen for testing purposes. Telephone set L can use either an internal battery or power from a Central battery system, thus permitting use upon any telephone line.

An American instrument designed for testing purposes by linesmen and working in the field similarity to telephone set L. The components are mounted on a metal chassis, in a leather case complete with straps for carrying purposes.
Speech communication only. Powered by central battery system or own power (two 1,5V cells). Calls made by Generator or Buzzer. When employing Central battery system, removal of the handset calls the Exchange.

A portable D.C. Telegraphy instrument of high sensitivity. The Mk IV includes radio suppression condensers. The fullerphone, used in the forward areas, cannot easily be intercepted, and can be superposed on existing telephone systems when telegraphic communication is required between points served by such systems.
As the instrument is essentially D.C. operated and uses Morse signaling only, the range of working is limited only by line resistance and leakage and by interference from stray earth currents. Under normal conditions a current of 2,5 micro amperes is necessary for reliable communication. But the fullerphone will give readable signals with a current flow of 0,5 micro amperes; therefore in emergency, high resistance lines could be used. The range is 15-20miles.
Fullerphones can be connected in series with telephone set D Mk V, but not with Telephone sets F, because the latter have no D.C. conducting path between the line terminals when the handset in on the cradle.

A portable field telephone exchange built into pressed steel case. The 6 line Sw/Bd is suitable for use by battalion and artillery regiments. The 10 line Sw/Bd is suitable for use by Divisional Signals. The range of working is 8-10 miles using D.3 cable and 14-16 miles using D.8.

A distribution and protection instrument, fitted with fuses and lightning protectors, mounted in a steel frame.

Mainly used with Switchboard U/C Mk II 6 and 10line.

Designed for fixed telephonic communication and field use. Built on the unit principle to provide self-contained switchboards of 20, 40 and 60 lines. Up to three complete 60 lines assemblies may be used alongside each other and inter-connected.

This equipment is used by R.A. battery commanders as a means of communication to any one or all of the four guns in the battery.
The principal item in the apparatus is the Telephone L.S. No.2 control unit. A wooden box which opens to form a lid and a base.
Cable electric D.8 Mk.III twisted is run from each pair of line terminals to a Telephone L.S. No.2 loudspeaker, which is a moving coil loudspeaker. In the top of each loudspeaker is a "Press-to-Signal" switch which enable the No.1 of the gun to indicate to the commander (by means of the indicating bulb) that he wants to speak to the commander. By the No.1 speaking loudly into the loudspeaker, the commander is able to hear the message in his receivers headgear. For carrying purposes the loudspeakers clip together and can be carried.