Deep routes – the story of submarine cables

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All over the globe an unseen network sends data at the speed of light. Submarine communications cables lie on the ocean floor between continents, carrying telecommunication signals across the seven seas.


The first transatlantic cable relayed telegraph traffic across the Atlantic in the 1850s.

Queen Victoria sent a message to the US president James Buchanan mentioning ‘An additional link between the nations whose friendship is founded on their common interest and reciprocal esteem.’ It took about 17 hours to send using Morse code.

The early cables failed because of poor quality cable coating. After incremental improvements and material innovation Isambard Kingdom Brunel’s giant steamship, the SS Great Eastern, successfully connected Valentia Island in Ireland to Heart’s Content in Newfoundland – using approximately 4,000 Km of cable.

19th Century tech didn’t allow for in-line repeater amplifiers in the cables, so massive voltages were used to overcome the resistance of such huge distances. The distributed capacitance and inductance of the systems distorted the telegraph pulses in the line, reducing bandwidth and limiting data to about ten words per minute. Today, undersea fibre optic cables transfer tens of terabits per second.

TAT-1 (Transatlantic No. 1) was the first transatlantic telephone cable system. It was laid from Scotland to Newfoundland in 1956 and carried 36 telephone channels. Cables from this era are still usable but their capacity isn’t commercially viable in today's data hungry world. Some are being repurposed by scientists to measure earthquake waves and other geomagnetic events.

Modern deep sea cables are only about 25 mm in diameter, but thicker and heavier nearer to shore to protect them. The optic fibre used in contemporary cables has exceptional clarity and uses repeaters every 100 Kilometres to minimise distortion. Light is amplified as it passes through the fibre and capacity is increased further through wavelength-division multiplexing.

Error free transmissions at 100 Gbps over 6,000 Km across the Atlantic Ocean can be achieved, facilitating millions of transactions, conversations and data streams between America and Europe at any time.

Submarine cables are reliable, with multiple paths available in the event of a cable break. Antarctica is the only continent not physically connected to the global grid, the incredibly low temperatures and shifting ice-flows make the logistics impossible.

In warmer climates earthquakes, anchors and shark bites can damage cables. During the Cold War, Russia used fishing trawlers to damage American infrastructure, while the US Navy tapped Russian cables in Operation Ivy Bells. Sixty years earlier Britain and Germany routinely snipped each-others cables during World War I. Many new cables today are buried for safety.

President Buchanan’s response to Queen Victoria still resonates:

‘May the Atlantic Telegraph, under the blessing of Heaven, prove to be a bond of perpetual peace and friendship between the kindred nations, and an instrument designed by Divine Providence to diffuse religion, civilization, liberty and law throughout the world.'


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