A Fault in the Armour

Samuel Canning reduced the number of men working in the cable tank. The gentlemen accompanying the expedition volunteered to watch them. They would take turns, two hours at a time, while the cable ran out towards the Atlantic floor.

It was late July 1865. Canning, the engineer in charge of laying a telegraph line between Ireland and Newfoundland, had already stopped and recovered cable twice after electrical tests disclosed a fault. Inside the second damaged section was a short piece of metal wire. It passed through the protective covering and insulation to touch the copper conductor at the centre.

Somebody, it seemed, had attacked the cable. In his account of the voyage, the journalist William Howard Russell recorded the anger aboard Great Eastern and the suspicion directed at men working in the tank. Canning organised the extra supervision. There were still hundreds of miles of cable to lay, and no identified culprit.

The cable had been made to withstand a journey through machinery and into water more than two miles deep. Its armour was essential to that work. It would also become a leading suspect.

Seven wires, one circuit

At the centre of the 1865 cable, six copper wires wound around a seventh. Together they formed one conductor. They did not carry seven separate conversations. Stranding made the conductor more flexible and reduced the chance that a local weakness would break every electrical path at the same point.

Copper carried the current, but seawater could carry it away. Around the strand went four coatings of gutta-percha, a natural insulating material which softened with heat and set again when cool. Between its layers lay an adhesive insulating preparation called Chatterton's compound. The compound also filled the spaces between the copper wires, helping the covering grip the conductor and denying water an easy route along it.

Outside the insulated core was a cushion of jute. Around that came ten heavier metal wires, each wrapped separately in Manila yarn before being wound spirally around the core. The manufacturer, Webster & Horsfall, called the metal Homogeneous Iron. Contemporary writers described its strength as approaching steel's; cable engineer Fleeming Jenkin called the wires steel.

This outer assembly carried the tensile load as the cable was lowered or hauled back. The yarn helped protect the wires and reduced the cable's weight in water relative to its bulk. Beneath all of it, the gutta-percha had to remain unpunctured.

An earlier cable had crossed the Atlantic in 1858, then lost useful communication within weeks. Its failures had left more than a problem of finding another ship. Design, manufacture, testing and handling all required scrutiny. The later official inquiry found shortcomings across those stages. The electrical methods used to work the damaged line became a further controversy; there was no sound reason to treat it as a perfect cable destroyed by one isolated mistake.

The new conductor contained 300 pounds of copper per nautical mile, against 107 pounds in the earlier cable. More copper lowered resistance, but quality mattered as well as quantity. Apparently similar copper wires could differ considerably in conductivity. Material was selected by electrical measurement before it became part of the line.

A material already known in Asia

Gutta-percha reached the British factories through a trade centred on Singapore, drawing supplies from the Malay Peninsula and the Indonesian archipelago. People in the region had long used it for such things as tool handles. Its capacity to soften in hot water, take a shape and retain it on cooling had practical uses before British manufacturers encountered it.

It came from the latex of several forest trees, including Palaquium gutta. Turning the imported material into reliable insulation required removing dirt, moisture and cavities. Russell's description of the earlier Atlantic manufacture follows raw lumps through rasping, hot-water working, washing, pressure sieves and hours of kneading. Warm material was then forced through a die around the moving copper wire.

Demand carried a cost in the forests. Collectors commonly felled trees to obtain the latex. Singapore's large gutta-percha trees were rapidly depleted as exports grew in the 1840s. Material which could be reheated and shaped repeatedly in a factory was being gathered by a method which killed its source.

At the factory, a good insulating substance could still become a bad covering. Copper placed off-centre left a thin wall on one side. An impurity or air cavity could create a weakness. Joining manufactured lengths introduced another operation which a machine could not complete for the whole ocean crossing.

Looking for a leak

The Gutta Percha Company and the cable makers Glass, Elliot & Co. had merged in 1864 as the Telegraph Construction and Maintenance Company. The insulated core and its finished protective covering now belonged to one manufacturing concern. Inspection continued as the material moved between the stages.

For the 1865 cable, Russell describes the completed core soaking for twenty-four hours in water at 75°F, about 24°C, before measurement. Warmth reduced gutta-percha's insulating resistance. Testing at a stated temperature let electricians compare results, rather than mistake a warm coil for a faulty one or a cold coil for unusually good material.

The company buying the cable had observers repeat the contractors' electrical tests. The core also underwent pressure testing and was examined by hand as it was rewound. At Greenwich, reels waited in water-filled tanks with their lids locked until required for the next operation.

Water made defects easier to find. With the far end insulated, a battery and sensitive instrument could reveal current leaking from the copper through a damaged covering into the surrounding water. The same hole in a dry coil might reveal very little.

An apparently helpful coating had once frustrated this test. Tar applied to the padding could squeeze into a small flaw and temporarily stop its leakage. The core appeared sound until the imperfect seal ceased to protect it. Jenkin credited Willoughby Smith, the gutta-percha works' electrician, with recognising the danger. For the Atlantic cable, Russell says the jute was preserved with catechu, a plant extract, rather than given the old tar treatment. Water could reach a defective part of the actual insulation.

The finished cable went into enormous iron tanks and was tested again. Dudley's Greenwich view places men inside one of them, handling the cable as it was coiled. The factory needed to store a continuous line which could later leave in the right order. Great Eastern received her load in three large tanks.

Cutting out the bad place

The first fault of the voyage appeared on 24 July. Canning stopped laying and transferred the cable from the stern to the bow to haul it back. The recovery was slow: the boiler serving the machinery struggled to supply steam. A portable engine and boiler were brought forward to help.

On the morning of the 25th, after more than ten miles had been recovered, the damaged place came aboard. A piece of wire had penetrated the cable. That portion was removed and the ends joined again.

Joining meant restoring several different things. The copper needed electrical continuity; the insulation needed a watertight joint; the exterior needed mechanical strength. In his technical account published the following year, Jenkin described warming gutta-percha with a spirit lamp and working it by hand into the existing covering. Too much heat, too little heat or moisture could spoil the work. The jointer judged the heat through experience. The completed joint then had to satisfy an electrical test.

The second fault was detected on 29 July. Its recovery and examination brought the concealed piece of wire and the suspicion of sabotage. The wire's resemblance to the cable's own armour did not initially make the injury seem innocent.

On 2 August, another electrical fault stopped the ship. During the preparations to recover it, a foreman found wire projecting from cable still in the tank. As he took hold to prevent it catching, it broke off. Russell saw the fragment afterwards. Here was an alternative to an attacker: an armouring wire could break beneath its yarn, bend outwards and enter a neighbouring turn of cable.

Russell reported a substantial change of opinion aboard. Canning was less conclusive in his report to the directors on 22 August. He set out both accident and deliberate damage as possibilities, noting that similar broken wires had been found projecting from the coils. The evidence had supplied a plausible mechanism, rather than a confession or a culprit. Jenkin later explained how the separate yarn jackets could hide fractures until movement or feet on the coils drove an exposed end farther in.

A cable left on the bottom

The third fault had a different consequence. While Great Eastern was recovering cable on 2 August, a change of wind and difficulty controlling the stopped ship brought the line against her bow. Canning described chafing, an attempt to bring the injured parts aboard, then a sudden break. The cable slipped through the stoppers and went overboard.

He subsequently considered whether he should have continued laying with the electrical fault still present. His answer remained no. He could not expect a certificate that the line met its contracted electrical condition. The effort to remove a defect had exposed the cable to a mechanical danger which ended the crossing.

Attempts to grapple it that summer repeatedly failed to bring the end aboard. Ropes, connecting hardware and machinery gave way. The expedition returned with the unfinished cable on the seabed and more than a thousand miles still in the ship.

In 1866, the contractors returned with stronger recovery arrangements and a new cable. The new line retained the same broad construction, but its armouring wires were galvanised and their yarn covering was left free of the old tar treatment. Electrical arrangements allowed insulation to be watched while signals passed between ship and shore. That cable reached Newfoundland in July.

Great Eastern then returned for the line lost the previous year. On 2 September the recovered end was aboard and communicating with Ireland. It was spliced to cable in the ship, and laying resumed towards Newfoundland.

There was still another fault to cut out near the end. Bright's later account records a broken wire driven into the core as the cable left its tank on 8 September. The damaged portion was removed, another splice made, and that evening the recovered 1865 cable joined the new one in service.