The wikipedia article he links to goes on to explain the types of cables that we’re created under water to carry telegraph messages across the transatlantic.
Transatlantic telegraph cable
A transatlantic telegraph cable is an undersea cable running under the Atlantic Ocean used for telegraph communications. The first was laid across the floor of the Atlantic from Telegraph Field, Foilhommerum Bay, Valentia Island in western Ireland to Heart’s Content in eastern Newfoundland. The first communications occurred August 16, 1858, reducing the communication time between North America and Europe from ten days – the time it took to deliver a message by ship – to only 17 hours. Transatlantic telegraph cables have been replaced by transatlantic telecommunications cables.
Submarine communications cable
A submarine communications cable is a cable laid on the sea bed between land-based stations to carry telecommunication signals across stretches of ocean. The first submarine communications cables, laid in the 1850s, carried telegraphy traffic. Subsequent generations of cables carried telephone traffic, then data communications traffic. Modern cables use optical fiber technology to carry digital data, which includes telephone, Internet and private data traffic.
Reddit user KrazyTrumpeter05 adds to the discussion about last mile ISPs and the actions internet companies today are taking to spread connections worldwide “Last mile ISPs typically don’t have anything to do with international infrastructure like this. Guys like ATT and Verizon used to be in the cable game, but they aren’t really involved anymore. Now it’s mostly national governments trying to get their countries connected or private companies trying to make a business out of it. The last two years, however you’ve seen a big push from guys like Google/Facebook/Microsoft to build their own cables to handle linking all their major data centers.”
Another interesting point to consider is the wear and tear of the cables which run underwater, there is an abundance of sealife that is knawing away at infrastructure. Reddit user blorg says “They break all the time underwater as well, usually from natural processes but also from stuff like shark bites (sharks are attracted by the electricity) and ships dropping anchor. It’s only noticed in places where there are few cables going into the country (which is usually either very small, or developing countries). They break all the time between large developed countries as well but if you look at that map it’s clear one cable breaking in the Atlantic is unlikely to have a major effect because there are so many others to take up the traffic.”
[1,2] – https://en.wikipedia.org/wiki/Transatlantic_telegraph_cable