Hi Gary,
Pre-WW2 was mostly buzzer call instruments: Telephone Sets D Mark III and III* in leather cases, and a 10 line exchange (Buzzer Switch Unit 7+3). (For working in the "Danger Zone" (within about 3000 yards of the enemy lines) the Fullerphone (a Direct-Current telegraph instrument - morse only) would be used to prevent interception by the enemy (this was "point to point" only, it had no "calling features" and couldn't work through an exchange.
WW2 saw the introduction of Telephone Set D Mark V, with buzzer calling and buzzer or magneto answering. It could do morse code or speech, but was still interceptable, so the Fullerphone was still used if interception was likely to be a risk.
Linemen continued to use the D Mark III or a GPO 110 telephone for portability.
The "Office Telephone" for higher formations was Telephone Set "F", which originally supported buzzer and magneto calling, but later had the buzzer replaced by an "induction coil" (audio transformer) for better speech quality.
(The Telephone Set "F" High Power was for use on long lines and had a valve audio amplifier built in (separate battery boxes required)).
There was also Telephone Set 'H' in the same casing as the "F", which was "sound powered" (dynamic inserts for microphone and earphone) for short distance use (rifle ranges and coastal guns, etc.)
Telephone Set 'L' in a pressed steel case replaced the Linemen's phones. It was more robust but not waterproof and was later replaced by Telephone Set "J" which was fully sealed and tropicalised - this also replaced the "D" range as the Army dropped buzzer signalling from newer equipment.
Switchboards:
Universal Call 6-line and 10-line were used in forward areas, they supported buzzer or magneto signalling and are reasonably portable.
F&F (Field and Fixed) was a modular exchange that could be broken down for transit. It could also be connected to the GPO telephone network. (I can't put my hand on its manual right now, and can't remember if it supports buzzer signalling - depends on whether the indicators are sensitive enough.) It was basically an "Office" exchange for headquarters that was light enough (Ha!) to be taken into the field, as well as being used in fixed installations and vehicles.
Magneto 10-Line (WD) was a later (magneto only) switchboard that was waterproof. It required a separate telephone (usually a 'J') for the operator.
Various "Wireless Remote Control" units could also act as magneto telephones.
The 19 set group has most of the manuals if you need more detail.
Best regards,
Chris.
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