Satellite C-band usually transmits around 6 GHz and receives around 4 GHz. It uses large (2.4- 3.7 meter) antennas. These are the large white domes that you see on top of the cruise ships and commercial vessels.
C-band is typically used by large ships that traverse the oceans on a regular basis and require uninterrupted, dedicated, always on connectivity as they move from region to region. The shipping lines usually lease segment of satellite bandwidth that is provided to the ships on a full time basis, providing connections to the Internet, the public telephone networks, and data back-hauls to their head office.
C-band is also used for terrestrial microwave links, which can present a problem when vessels come into port and interfere with critical terrestrial links. This has resulted in serious restrictions within 300Km of the coast, requiring terminals to be turned off when coming close to land.