ofcourse bro, its fibre optic cables network down the bed of the sea, I came to know it when the internet was out in a region of Pakistan due to the breakage of fibre optic cable, a ship was sent to the location in sea and it took 3 days to repair.
but a country has sattelite and wireless links with the rest of the world as well which are used for alternative if such situation occurs.

yeah its true, fibre optics cables are used because its information carrying capacity is much greater than copper wire.fibre optics cable are totally different from other types of cables ,it works on the principle of total internal reflection and data will be send and receive using laser beam.