https://www.theverge.com/c/24070570/internet-cables-undersea-deep-repair-ships
If, hypothetically, all these cables were to simultaneously break, modern civilization would cease to function. The financial system would immediately freeze. Currency trading would stop; stock exchanges would close. Banks and governments would be unable to move funds between countries because the Swift and US interbank systems both rely on submarine cables to settle over $10 trillion in transactions each day. [...]
Corporations would lose the ability to coordinate overseas manufacturing and logistics. Seemingly local institutions would be paralyzed as outsourced accounting, personnel, and customer service departments went dark. Governments, which rely on the same cables as everyone else for the vast majority of their communications, would be largely cut off from their overseas outposts and each other. Satellites would not be able to pick up even half a percent of the traffic. [...]
Fortunately, there is enough redundancy in the world’s cables to make it nearly impossible for a well-connected country to be cut off, but cable breaks do happen. On average, they happen every other day, about 200 times a year. The reason websites continue to load, bank transfers go through, and civilization persists is because of the thousand or so people living aboard 20-some ships stationed around the world, who race to fix each cable as soon as it breaks.