Electronic Warfare in WW1- The Telegraph War (3)

The threat of German raiding parties was not lost on other parts of the World. In Canada troops were despatched to guard telegraph stations on both Pacific and Atlantic coasts. In New Zealand the coastal forts, with their disappearing guns, were manned. However with the destruction of the German squadron at the battle of the Falkland Islands, the loss of the Emden and the fall of the port of Tsientao Germany had no naval force outside European waters that could threaten the international cable network.
Tapping the Telephones.
The Western Front was festooned with the wires of trench and field telephone and telegraph systems. Although the official British Army instruction was to bury these at least a foot and a half this was not always possible in the heat of an action. Other armies on both sides would have the same problem and wires might be laid across the open ground, draped across the tops of trenches and shell holes, lie under duck boards, be tacked along the sides of trenches or even properly buried. As the trench line altered with minor advances and retreats some wires might end up crossing from friendly trenches across no mans land through enemy positions and back to ones own side. Where enemy wires were spotted exposed in no mans, land men might crawl out at night and lay wires to tap them. In other cases shell fire or even the inadvertent clumsy boot might break the wires. In some cases, when the line was thinly manned or sentries inattentive, wire taps were even laid onto cables in the enemy’s trench. The trench telephone and telegraph system on either side was not secure or reliable.
However the British began to get a sense that their calls were being intercepted with alarming ease. This was serious as the enemy might, for example, gain advance warning of a trench raid or learn when the line was thinly manned. However no one could work out why this was so. It became the common practice not to pass any important information by the trench phones but to rely on despatch riders and runners even with the risk of additional casualties to the messengers. At the same time emergency signalling methods such as warning rockets were kept handy as, with the predictably malignity of inanimate objects, the trench phone would fail just when a call for help was needed.
The cause of the security problem was found by accident when a signals instructor, Sgt Lorne Hicks, on a course in Canada found that his phone was picking up the signal of the man next to him. The British field telephone relied on a ground return system. In this the phones are connected by a single wire with the ‘second wire’ of the circuit being a short wire to a spike in the ground. The AC current on the phones was creating a signal through the ground that could be picked upon devices known as Moritz Stations. It was worse (easier to pick up) when the phone was being used to transmit Morse buzzes (as was the case over long lines). As the Germans perfected the sensitivity of the Moritz Stations they could ‘bug’ a phone from a kilometre away. Moreover, as the signal was transmitted through the ground, by creating underground saps towards the British lines they could sit at its end and pick up even more signals. One interesting sidelight to this is that the German monitors frequently picked up a whistling noise that sounded like the screech of a descending shell. Known as ‘screamers’ these were at one time thought to be artificial noises made by British operators attempting to ‘jam’ the interception; they are now known to have been created by the solar wind hitting the ionosphere – true signals from outer space.
Once the problem was identified attempts were made to find ways to intercept the German trench telephones by picking up the magnetic induction from operation of the speaker or buzzer. How successful this was is unknown as the results were classified and seem to have been lost for ever in the labyrinth of military secrecy. At the same time a British device called the Fullerphone, the invention of a Captain (later Major General) A C Fuller in 1915, was investigated and then adopted. The Fullerphone could send Morse over a 20 mile long single wire line and voice over a shorter distance. On some versions of the device it could send Morse and voice simultaneously along the same line (effectively what your broadband modem does only it’s much much faster). When used on normal phone lines distance was not a problem. It used a DC signal that was much less powerful than the old trench telephone and therefore much more difficult for the Moritz Stations to pick up. At the same time the Morse system depended on a device in each phone called a ‘buzz chopper’, the people at each end had to synchronise their buzz choppers, these acted as a scrambling device so that no third party could listen in. As a bonus it was found that the Morse signals could be transmitted over damaged lines and across breaks (provided each side of the break was in ground contact and not too far apart).

Picture Field telephone exchange