Subsea cables were not new in 1866: shorter cables were in service from 1851, first across the English Channel and later on other routes in North America, across the Irish Sea and in the Mediterranean.
The first transatlantic cable was laid in 1858, but it lasted just three weeks in service.
The Great Eastern steamship tried to lay a better designed cable in 1865, running from Ireland to Newfoundland, but the cable broke 1000 kilometres from Newfoundland.
The following year the Great Eastern was successful; the ship then went back and grappled up the 1865 cable and completed the connection.
Commercial service started on 28 July. Those early cables lasted just a few years, but before they went out of service new cables had been funded and laid. Since then, Europe and America have never been out of telecommunications contact – though the international cable industry is not marking the anniversary with much of a celebration. (The Newcomen Society, which specialises in industrial history, has a conference at the Royal Institution in London on 5 September – that seems to be all.)
A London company called Telcon built the 1865 and 1866 cables in its factory by the River Thames in Greenwich, south-east London. In the century and a half since, the company has operated under several names. It became part of Standard Telephones and Cables (STC), a US-owned company at whose UK laboratories Charles Kao invented optical fibre communications: he won the 2009 Nobel Prize for physics.
More recently the business has been Alcatel-Lucent Submarine Networks, owned by Nokia since early 2016.
Nokia still occupies part of the original Greenwich site, where it makes submarine cable repeaters. It is, almost certainly, the oldest continually operating telecoms factory in the world. There are local moves to preserve Enderby House, the company's former head office which is now surrounded by newly built apartment blocks.
The original cable operator, Anglo-American Telegraph Company, eventually became Cable & Wireless. Vodafone bought part of the business in 2012 and Liberty Global the rest earlier in 2016.
