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Fullerphone

For many years I have been intrigued by the Fullerphone. Over the last 30 years I have gathered much information of its history, operation and practical use. On this web page I have compiled some basic historical and technical information about this relatively unknown, but very remarkable DC Morse telegraph.

Fullerphone Mk.IV*.

The Fullerphones Mk.IV and Mk.IV* were the most widespread models.

Fullerphone inventor.

Maj. Gen. A.C.Fuller CBE, the inventor of the Fullerphone, showing his Princess Mary medal.

Ode to a Fullerphone


By Sigmn R.MELLOR, published in 'Jimmy', the WW2 journal of the Royal Corps of Signals in the Middle East.



What is my greatest joy in life,

More precious even than my wife,

So comforting 'midst all this strife?

My Fullerphone.


How well I love your merry tricks;

Even when your buzzer sticks;

Delighting me with faint key clicks;

Oh Fullerphone.


How tunefully your buzzer throbs

As tenderly I turn those knobs.

Most fascinating of all jobs.

Oh Fullerphone


Potentiometer, its true

I'm not sure what to do with you.

Yet even you add beauty to

My Fullerphone.


Oh how I pity those poor souls

Who daily work remote controls,

Attached to crazy wireless poles.

Oh Fullerphone.


They never hear the tuneful tones

Of perfect Morse within their 'phones:

Just atmospherics, shrieks and groans.

Oh Fullerphone.


But I must cease to write more verse.

Communication getting worse.

No wonder that I rave and curse

At Fullerphone.


Asthmatic buzzers, - crazy keys.

How can one live a life of ease,

With damful instruments like these

Foul Fullerphones!

Fullerphone in Tobruk.

Tobruk-1942... A row of Mk.IV Fullerphones in use at an Australian headquarters in the Western Desert.

Next page (Fullerphone principle)

Australian Long Range Fullerphone


When operating the Fullerphone over longer ranges and/or noisy lines the signal to noise ratio could be improved by means of additional cells at each instrument, and reducing the strength of the received signal to the normal value by means of a volume potentiometer.

This was accomplished in the Fullerphone Mk.IV* Special (Aust.) with Unit Fullerphone Long Range (Aust.). Obviously, with an increase of line current the signals were more liable to interception. Download a copy of the ‘Signal Training Volume III, Pamphlet No. 21- Fullerphones, Mk.IV, Australian addendum, No. 1’ in the Documents section on the Downloads page.

During World War Two cases arose where submarine cable circuits were available but the necessary terminal equipment was found to be totally destroyed or not immediately available. To ascertain to what extent Fullerphones could be used on submarine cables of various lengths, trials were carried out by Cable and Wireless Ltd on request of the War Department. The results exceeded all expectations, and ranges of up to 700 miles were obtained with faint but readable Morse signals at a maximum of 20 words per minute.

Further reading:


The Fullerphone (Pt 1-4). Its Action, Uses and possible Future Uses.

By O.F. Mingay, Australasian Electrical Times, Dec. 1922-May 1923.


The drop of potential method for fault location - application of Fullerphone. Published in The Telecommunication Journal of Australia, Oct. 1947.


The Fullerphone, and its practical application to military and civil telegraphy.

By Major A.C. Fuller, IEE Journal, 1919.

Fullerphone submarine cable.

Circuit diagram of Fullerphones connected to a long submarine cable.

Historical development


World War One.. two large armies were densely packed in their trenches, at places only a few hundred yards apart. Signal communication was principally by telephone and various buzzer telegraph instruments, connected via single line and earth return. The earth was thus alive with buzzer and telephone induction.

During mid-1915 the Germans were extraordinary well informed of Allied plans. Carefully planned raids were met by hostile fire exactly timed and directed. Relieving troops would be greeted, if not by shells, by shouts of welcome from the opposing trench.

On one occasion a Scottish battalion took over its new front to the strains of its regimental march played by a German cornet! Espionage was suspected but an interned British civilian brought back the information that induction of lines led to widespread overhearing of signals.

Hastily conducted experiments carried out within the Allied lines left no doubt about the cause of the leakage, and measures against eavesdropping were rapidly introduced by using metallic circuits (twisted pair of wires instead of an earth return) within 3 miles from the front line.

The ultimate solution to this problem came toward the end of 1915 when Captain A.C. Fuller devised the Fullerphone. In October 1915 Fuller brought two prototypes to 5 Corps in Flanders. His invention was tested on a five mile loop of cable, part of which ran in the water-filled moat of Ypres, with a 10 Ohm leak to earth. The instruments worked well and were obvious the answer to the problem of overhearing which had brought the British Expeditionary Force signal system almost to a standstill.  Source: R.E. Priestley, MC, BA, ‘The Signal Service in the European War of 1914 to 1918 (France)’


Used in two wars


Initial issues of Fullerphones were made up from converted field telephone sets. This type, however, appeared to be not the most successful. Towards the end of 1916, the Fullerphone was firmly established, and by 1918 most divisions had adopted Fullerphones for all their forward communication circuits. After the Armistice, more improvements and modifications of the instrument were carried out. The basic principle, however, was never changed. In about 1937 a fully re-designed model, the Mk. IV, went into service. This (and its later variations) can be considered as the most successful model, not only being more sensitive than its predecessors, it had also a simplified buzzer-chopper, and was easy to use as it carried no telephone set. Although the Fullerphone was devised as a non-overhearable signalling set for static warfare, it was again widely used during World War Two because of its capability to work simultaneously with a telephone over the same line and working through very long or leaky lines where telephone or telegraph traffic was impossible. In the South West Pacific, for example, the Australians made extensive use of the Fullerphone, notably in New Guinea.