In 1866, a transatlantic telegraph cable was laid between Valentia Island, Ireland and Newfoundland, Canada, and the first messages were exchanged. The transmissions took several hours to cross the ocean – at a time when communications would have taken days by ship.
The cable was built at Greenwich, by the Telegraph Construction and Maintenance Co. Some 2500 miles of it were loaded into hulks at the Greenwich docks and carried downstream to the waiting cable ship.
The ship that laid the cable was the Great Eastern, designed by British engineer Isambard Kingdom Brunel. Larger than any passenger vessel of her time, but with a succession of owners bankrupted by outfitting costs and subsequent accidents, her structure was specially modified to carry the cable coils and to slowly pay out the cable into the ocean depths.
Faults in the cable insulation and breakages in the copper core were detected by measuring the electrical resistance of the signal as the cable was paid out along the route. However, recovery of the cable from the water was a laborious operation and when a fault was discovered not far from Newfoundland, the cable snapped under the strain of its own weight while it was being raised. A year later, the broken end of the cable was found by grappling across the ocean floor. It was eventually raised and spliced into a new length of cable before the cable run was completed.
Early cable designs had significant electrical shortcomings which limited the bandwidth of the cable.
Now, over one hundred and fifty years later, the oceans are criss-crossed by telecommunications cable routes. New cables contain a fibre optic core; with optical amplifiers or repeaters along the length of the route. The electrical characteristics of the cable are still an important fault finding tool.
Specialist marine survey and cable laying vessels, and the analysis of water depths, sea bed composition, sea bed temperatures, the location of maritime boundaries and other submerged equipment crossings such as oil and gas pipelines all make up the complex landscape of submarine cable installations.
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