The first submarine cables were laid in the 1850s, to carry telegraphy traffic, as technology advanced, submarine cables were upgraded to carry telephone and data traffic. Modern cables use optical fiber technology to carry digital data (telephone, Internet and private data traffic).
More than 99 percent of the world’s Web traffic is dependent on these underwater cables, and there are many many of them.
Check out this map below of all the submarine cables in the world put together by TeleGeography:
You can check out a complete interactive map on their website here: http://submarine-cable-map-2015.telegeography.com/